Sataloff’s Comprehensive Textbook of Otolaryngology: Head & Neck Surgery (Head and Neck Surgery) - Volume 5 Robert T Sataloff, Patrick J Gullane, David P Goldstein
INDEX
×
Chapter Notes

Save Clear


The Molecular Biology of Head and Neck CancerCHAPTER 1

Jason I Kass,
Jennifer R Grandis
 
INTRODUCTION
Molecular biology has revolutionized our understanding of cancer biology. In the past 60 years, we have progressed from primarily using histopathology to now recognizing biomarkers, like p16, and assigning a molecular phenotype. Disease prognosis based on molecular information is now a reality, and clinical trials are underway to further personalize treatment based on molecular features. As an oncologic head and neck surgeon, it is essential to be familiar with the important molecules that are either inactivated or dysregulated in head and neck squamous cell carcinoma (HNSCC), particularly as our armamentarium of targeted therapies grows. Here, we review the molecular pathways implicated in HNSCC and the targeted therapies that are available or emerging.
 
MOLECULAR CHANGES ASSOCIATED WITH HISTOLOGICAL CHANGES IN SQUAMOUS EPITHELIUM
HNSCC is a heterogeneous entity initiated over time through repeated exposure to carcinogens, the major ones being tobacco and alcohol. In 1953, the term “field cancerization” was coined to recognize that there were separate populations of cells in close proximity that could give rise to second primaries despite having clear surgical margins.1 With advances in molecular biology a genetic model of progression from normal mucosa to invasive HNSCC was first proposed in 1996.2 In this series, 83 patients were followed with serial biopsies. Specimens showing dysplasia, carcinoma in situ (CIS), and invasive cancer were analyzed by PCR, and a series of chromosomal regions containing key oncogenes/tumor suppressor genes were analyzed. A loss of heterozygosity (LOH) was seen in nearly all of the specimens with dysplasia or CIS. LOH of the tumor suppressor genes p53 and p16 was seen as early changes as the mucosa became dysplastic (Fig. 1.1). LOH of the tumor suppressor gene retinoblastoma (Rb) and cell cycle protein cyclin D1 were detected in CIS and loss of genes in chromosomes 6p, 8, and 4q was identified in invasive tumors.3 Cells accumulated these mutations over time, and there was heterogeneity within different specimens, although they appeared the same histologically. This work supported the molecular underpinning to the heterogeneity seen in field cancerization 40 years earlier.
With advances in sequencing technology, the expression patterns of an entire genome could be assayed in individual tumors.4 Messenger RNA extracted from normal and premalignant mucosa as well as invasive cancer specimens from 21 patients revealed several hundred genes that were either upregulated or downregulated in premalignant tissues. Fewer genes had transcriptional changes as they progressed from premalignancy to invasive cancer. The genes identified were involved in nearly all of the cellular processes disrupted in cancer including the cell cycle, cell growth, cell adhesion, blood vessel ingrowth (angiogenesis), and regulated cell death (apoptosis).
Most recently, advances in high-throughput sequencing technology have allowed for whole-exome sequencing (exons of all expressed genes) of nearly 125 squamous cell 2tumors.5,6 This data set, published by two separate groups in 2011, confirmed the importance of genes previously implicated in HNSCC, but also highlighted new genes not previously thought to be involved in disease progression (Table 1.1).
 
Terminology: Oncogenes, Tumor Suppressor Genes, and Mutations
Genes that allow for uncontrolled cancer cell growth fall into two classes: proto-oncogenes and tumor suppressor genes.
zoom view
Fig. 1.1: Molecular alterations associated with histologic changes in squamous epithelium. Early events including mutations in p53 are seen in dysplastic mucosa, whereas late events such as PIK3CA activation and PTEN inactivation are seen in invasive cancers.
Table 1.1   Tumor suppressor genes and oncogenes in head and neck squamous cell carcinoma
Gene
Classification
DNA location
Frequency of genetic alteration5,22
Cell proliferation pathways
TP53
Tumor-suppressor
17p13
Inactivating mutation/deletion (63%)
RB1
Tumor-suppressor
13q14
Inactivating mutation/deletion (3%)
CDKN2A
Tumor-suppressor
9p21
Inactivating mutation/deletion (25%)
CCND1
Proto-oncogene
11q13
Amplification (22%)
TGFBR2
Tumor-suppressor
3p22
Inactivating mutation/deletion (*)
SMAD4
Tumor-suppressor
18q21
Inactivating mutation/deletion (*)
Cell signaling pathways
EGFR
Proto-oncogene
7p11
Amplification (90%)
HRAS
Proto-oncogene
11p15
Activating mutation (4%)
PI3KCA
Proto-oncogene
3q26
Activating mutation (8%)
PTEN
Tumor-suppressor
10q23
Inactivating mutation/deletion (8%)
Cell differentiation pathways
NOTCH 1 (2,3 as well)
Tumor-suppressor
9q34
Inactivating mutation/deletion (22%)
TP63
Proto-oncogene
3q26
Activating mutation or amplification (8%)
Cell death
CASP8
Tumor-suppressor
2q33
Inactivating mutation (8%)
Virally-mediated pathways
E6
Viral oncogene
Human papilloma virus (HPV)
N/A
E7
Viral oncogene
HPV
N/A
* Indicates that the two genes in the transforming growth factor beta pathway were not in the top 74 highly mutated genes identified in the study of Stransky et al.5 (N/A: Not applicable).
3
Proto-oncogenes have the potential to become oncogenes, confer a survival advantage, and drive cancer progression. Only one copy of the gene requires an activating mutation for the proto-oncogene to become oncogenic. In HNSCC, the catalytic subunit of phosphatidyl-inositol-3-kinase (PI3KCA) is a proto-oncogene. Mutations in this subunit can activate the kinase, driving cell division through downstream targets.7 In contrast, tumor suppressor genes act to hamper uncontrolled cell growth. Tumors must overcome these genetic brakes by either mutating both copies or by losing a gene copy by LOH and then sustaining a second inactivating mutation. In HNSCC, p53 is a central tumor suppressor gene.8 It is mutated in nearly 65% of HNSCC and is a multifunctional protein that regulates entry into the cell cycle as well as directing cells toward apoptosis.9
Mutations of proto-oncogenes and tumor suppressor genes can occur through a wide variety of mechanisms, and the literature supports the entire spectrum of known mutation types in HNSCC. There are point mutations that can result in missense or nonsense mutations, duplications, translocations, insertions, and deletions. Interestingly, in HNSCC, transversion mutations, where the purine guanine was substituted for the pyrimidine thymidine, were observed much more frequently in smokers.5,10
 
Cell Proliferation (p53, Rb, CDKN2A, CCND1)
The cell cycle is one of the most conserved pathways in biology with gene homologs in the simplest eukaryotes including yeast.11 As such, it has evolved tightly regulated checkpoints to prevent the disorganized and uncontrolled growth seen in cancer. Important cell cycle regulatory genes that are either mutated or downregulated in HNSCC include TP53 (p53), Rb (retinoblastoma), CDKN2A (cyclin-dependent kinase 2A), and CCND1 (cyclin D1).
p53 is the most commonly mutated gene in HNSCC.12 It is one of the earliest mutations seen in dysplastic mucosa, and either inactivating mutations or downregulation of p53 expression was seen in 80% of the whole-exome sequencing data.5 p53 is a multifunctional protein that primarily acts as a master tumor suppressor gene.9 It contains a DNA-binding domain and acts as a transcription factor, turning on genes that suppress the cell cycle, induce apoptosis, and inhibit autophagy (intracellular protein turnover). In the cell cycle, p53 tetramers prevent progression into mitosis at the G2-M checkpoint by activating p21 and irreversibly leading to cell cycle arrest (Fig. 1.2).3 Although its effects as a transcription factor are well appreciated, p53 is multifunctional. In the absence of a DNA binding domain, p53 remains able to have both cytoplasmic and nuclear effects. In vitro experiments with mutated forms of p53 that lack the DNA binding domain induce apoptosis.9
Retinoblastoma, cyclin D1, and cyclin-dependent kinase inhibitor 2A are the proteins encoded by Rb, CCND1, and CDKN2A genes. These proteins are important for entry into the cell cycle and transition from G1 interphase to DNA synthesis by passing the G-S checkpoint. The critical step for DNA synthesis is the release of the transcription factor E2F.3 Normally, E2F is inactive and bound tightly to the retinoblastoma pocket proteins (Rb is the canonical member of a larger family). When the balance between cellular senescence and growth is tipped toward growth, the growth inhibitor CDKN2A (also called p16Ink4A) is inactivated leading to cyclin D1 complexes with cyclin-dependent kinases CDK4 and CDK6.
zoom view
Fig. 1.2: Regulation of the cell cycle at the G1-S and G2-M checkpoints. Asterisks (*) indicate the respective checkpoints. Mutations in key regulatory proteins like p16 (CKDN2A), Rb, and p53 can abrogate checkpoint integrity and promote unregulated cell division.
4
Cyclin D1-CDK4 or CDK6 complexes lead to partial inactivation of Rb. The pocket proteins are then further inactivated by cyclin-E activation of CDK2. Complete inactivation of Rb allows for release of E2F and DNA replication proceeds.
Amplification of cyclin D1 is an early event in the progression from premalignant to invasive carcinoma.13 Overexpression of cyclin D1 is associated with poor prognosis in HNSCC with studies showing both worsening survival14 and higher recurrence rates.15 Whole-exome sequencing showed amplification in 22% of patients. Deletion of CDKN2A is also a poor prognostic indicator16 and was seen in 25% of HNSCC tumors analyzed by whole-exome sequencing to date.
 
Cell Signaling (EGFR, RAS, PI3KCA, TGFBR2, SMAD4)
There are a number of signaling pathways dysregulated in HNSCC, and targeting these pathways represents some of the most exciting targets for selective drug therapies in HNSCC (see below). The most established signaling pathway is the epidermal growth factor receptor (EGFR) (Fig. 1.3). EGFR is a receptor tyrosine kinase that dimerizes to transduce its signal through several intracellular pathways, including the RAS-MAPK, PI3K-PTEN-AKT, JAK-STAT, and phospholipase C pathways.17 Interestingly, EGFR (also called ErbB-1; HER1 in humans) may have a dual role. EGFR can either act as a membrane bound receptor, forming dimers with itself and other members of the ErbB/HER family, or it can translocate to the nucleus and act directly as a transcription factor.18 Recent evidence with a tagged form of EGFR showed nuclear localization and association with the promoter region of cyclin D1. It suggests that the receptor itself can directly upregulate cyclin D1 to control the cell cycle.
Although activating mutations in EGFR have been described in HNSCC, they are relatively uncommon.1921 Instead, amplification of EGFR appears to be its mechanism for driving cell growth in 90% of patients.22 One activating mutation, EGFRvIII, is a truncated form of the receptor that lacks the extracellular binding domain and is constitutively active.23
The PI3K-PTEN-AKT-mTOR signaling cascade is another important pathway in HNSCC, because it appears to contain one of the few proto-oncogenes in HNSCC and may serve as a new target for selective drug therapy.24
zoom view
Fig. 1.3: Key signaling pathways in head and neck squamous cell carcinoma (HNSCC). Epidermal growth factor receptor has wide-ranging intracellular effects in both modulating cytoplasmic enzymatic cascades (via MAPK-Ras pathway) but also at the level of gene transcription. PI3K-PTEN-AKT pathway inhibits apoptosis (via BAD-BIM) and drives cell growth and division through its effects on p53 and cyclin D1. TGF-β pathway inhibits cell growth and disruption of integral components (TFGBR2, Smad4) removes inhibitory signals in HNSCC.
5
As described above, most of the major genes identified in HNSCC are tumor suppressors. PIK3CA encodes the alpha catalytic subunit for the protein phosphatidyl-inositol-3-kinase and is mutated in approximately 8% of HNSCC.5 This enzyme phosphorylates the cell membrane constituent phosphatidylinositol-1,4-bisphosphate (PIP2) to phosphatidylinositol-1,4,5-trisphosphate (PIP3). PIP3 then attracts another kinase, which selectively activates the proteins AKT and mammalian target of rapamycin (mTOR). AKT and mTOR are serine/threonine kinase with pleotrophic effects including inhibition of the apoptosis proteins (BAD and BIM), cell cycle inhibitors and inhibitors of p53. Thus, activation of this pathway strongly favors growth. To turn off this pathway, a phosphatase, PTEN, inactivates PIP3 to PIP2. Ten percent of HNSCC have inactivating mutations or deletions of PTEN. In cells where there is both inactivation of PTEN and activation of PIK3CA, there are no known regulatory controls of the AKT-mTOR pathway.
In contradistinction to the PI3K-PTEN-AKT-mTOR pathway, which favors growth and cell division, the actions mediated by the cytokine transforming growth factor beta (TGF-β) inhibits growth, favors differentiation and apoptosis.25 In normal epithelium soluble, TGF-β forms a heterodimer with the membrane-bound TGF-β receptors 1 and 2. The TGF-β receptors have serine/threonine kinases in their intracellular domains and after binding with TGF-β phosphorylates transcription factors called Smads (so called because they are similar to the Sma and MAD genes in fruit flies and worms). In epithelial cells, Smad2 and Smad3 are phosphorylated, form a complex with Smad4, and then translocate to the nucleus. The nuclear Smad complex has wide ranging inhibitory cellular effects. It potently suppresses cell proliferation by activating genes, like p15, to prevent Rb phosphorylation, (inhibiting E2F release) and preventing entry into the cell cycle. It also stimulates production of cell adhesion proteins including collagen and integrin, inhibits enzymes like collagenase, and others that breakdown the extracellular matrix. Activated TGF-β receptors can also mediate intracellular changes independent of the Smad complex. TGF-β favors apoptosis through both Smad-dependent and Smad-independent interactions.
Since the normal cellular effects of TGF-β are largely antioncogenic, TGFBR2 and SMAD4 act as tumor suppressor genes. Loss of chromosome 18q, which contains SMAD4 is common in invasive HNSCC.26,27 A recent mouse model has shown that loss of Smad4 in mouse oral mucosa causes HNSCC.28 Loss of Smad4 in patients with esophageal squamous cell carcinoma correlates with more invasive tumors,29 higher likelihood of local metastases and reduced survival.30
 
Cell Differentiation (NOTCH, TP63)
The Notch pathway has gained recent attention in HNSCC because it is mutated or deleted in over 20% of patients. Notch is an evolutionarily well-conserved protein, first identified in a screen of the fruit fly Drosophila melano-gaster because of its characteristic notched wing. It has previously been implicated in other cancers, particularly leukemia and lymphoma where it acts as an oncogene. In HNSCC, however, NOTCH mutations appear to be inactivating, implying that it acts as a tumor suppressor, although functional data are still lacking.
NOTCH1 is a member of 4 Notch receptors in humans. It is a large transmembrane poplypeptide with an intracellular domain that is cleaved following ligand binding and activation (Figs. 1.4A and B). The cleaved Notch intracellular domain translocates to the nucleus where it regulates genes involved in cell differentiation and cell survival.31 One important gene inhibited by Notch1 is TP63.32 TP63 encodes the protein p63, which is a homolog and member of the p53 family. p63 inhibits apoptosis and terminal differentiation and as such acts as a proto-oncogene. There is a direct reciprocal repression between Notch1 and p63. This interestingly is seen as a gradient of activity in epidermal layers. In basal layers where cell division is high and differentiation is low, there is elevated p63 expression and low Notch expression. In suprabasal layers where keratinocytes mature the expression pattern is reversed. Both Notch1 and p63 were highlighted as common mutations in the whole-exome sequencing data.6 NOTCH1 and its family members NOTCH2 and 3 are putative tumor suppressor genes that were mutated or deleted in 22% of the patients sequenced. TP63 is a putative oncogene that is mutated or amplified in 8% of patients.
 
Cell Death (CASP8)
Apoptosis or programmed cell death is an established means for cells to detect injury or germline mutations and prevent propagation. For a cancer cell to survive it must not only drive replication, but also avoid triggering its own death. The apoptotic pathway is complex and involves caspases, which are proteases that cleave a host of proteins.33
6
zoom view
Figs. 1.4A and B: Reciprocal role of Notch and p63 in driving cell differentiation and growth. (A) Basal epithelial layers are activity dividing and express low levels of Notch and high levels of p63. This reciprocal relationship is reversed as cells differentiate in more superficial cell layers. (B) The canonical Notch pathway with activation by adjacent cells and translocation of the cleaved Notch intracellular domain (NICD) to the nucleus.
They are translated as inactive zymogens until remain inactive until they form active caspase tetramers. There are a number of caspases that when stimulated initiate the apoptotic cascade. Caspase 8 is important in HNSCC and was found to be mutated in 8% of patients.
 
HPV-Associated Viral Molecular Mechanisms of HNSCC
The emergence of human papilloma virus (HPV)-associated HNSCC (HPV + HNSCC) has fundamentally changed the epidemiology of HNSCC. The patients are younger and do not necessarily have the typical tobacco and alcohol exposure as risk factors in HPV negative disease. In many ways HPV-associated disease is an entirely new disease entity. It has specific tissue-site proclivity, distinct clinical presentation, and unusual radiosensitivity. In addition, there is emerging evidence that classic indicators for poor prognosis, like extracapsular spread, may not apply to HPV + HNSCC.34,35 HPV has a particular tropism to epithelial tissue. In particular, it is the major driver for cervical cancer. In the head and neck, it has a proclivity for the lymphoid tissue of the oropharynx. There are over 120 different HPV genotypes, which have been categorized into high-risk (15 members) and low-risk subtypes based on their risk of causing invasive cervical cancer.36 HPV-16 is the most common associated subtype found in HNSCC biopsies (85-95%) and is a high-risk subtype. Some low-risk subtypes including HPV-6 and 11 are associated with benign oral cavity and oropharyngeal papillomas; however, these lesions can undergo malignant transformation, for example, in verrucous carcinoma. The proposed viral mechanism of carcinogenicity for HPV highlights the molecular underpinnings of cancer as the virus hijacks the normal cellular machinery to drive sustained replication.
HPV is a small DNA virus (Figs. 1.5A to C). Its genome is approximately 8000 base pairs in length. The HPV-16 genome is composed of 9 genes, 7 “early” genes E1-E7, and 2 “late” genes that encode the capsid. Like many viruses, its genome does not encode for any enzymes and must use host machinery to replicate, assemble, and exit to infect other cells. In a typical acute HPV infection the virus enter through microscopic breaks in the skin, during sexual activity, and infects the basal cells of stratified squamous epithelia. These basal cells are the actively dividing progenitor cells of the suprabasal layers, which become differentiated, but do not normally continue to divide. Once infected the virus exists as a circular episome and drives continual replication of the suprabasal cells. Of the 7 “early” genes, HPV E7 binds to the Rb family of proteins (Rb, p107, p130) and targets them for degradation. As in the normal G1-S check point, Rb degradation results in the release and activation of E2F and DNA replication. In addition to driving replication HPV, E6 binds p53 and targets it for degradation. E6 and E7 therefore effectively prevent cells from entering apoptosis and allow cells to replicate unchecked by the cell cycle. All HPV subtypes express E6 and E7. What makes the high-risk subtypes more aggressive is their high affinity of E6 and E7 for p53 and Rb.
7
zoom view
Figs. 1.5A to C: Oncogenic mechanisms associated with the human papilloma virus (HPV) and head and neck squamous cell carcinoma. (A) HPV-16 is a small DNA virus with a genome encoding for early and late proteins E1-E7, L1, and L2. (B) Direct inhibitory effects of E6 on the G1-S checkpoint and E7 on the G2-M checkpoint. (C) Additional effects of E6 and E7 on apoptosis, chromosome length, extracellular matrix proteins, and genetic instability. (TERT: Telomerase reverse transcriptase).
It is important to recognize that E6 and E7 interact with many cellular proteins to exert its oncogenicity (Fig. 1.3).36 In addition to binding p53, E6 inhibits apoptosis through interactions with caspase-8, and two pro-apoptotic proteins BAX and BAK. E6 also promotes cell immortalizaton by interacting with telomerase and telomerase reverse transcriptase to prevent chromosomal shortening. E6 binds to cell adhesion proteins so that cells can divide without being attached to an extracellular matrix. E7 similarly has multiple intracellular interactions beyond Rb. E7 can drive cell proliferation by either inhibiting cyclin-dependent kinase inhibitors p21 and p27, or directly activating cyclins and cyclin-dependent kinases. E7 also inhibits apoptosis and avoids immune surveillance by interacting the interferon regulatory factor 1 (IRF1). Finally, E7 can itself cause genomic instability by damaging DNA and activating the DNA damage response pathways (ATM-ATR).
 
TARGETED DRUG THERAPY IN HNSCC
 
Target: EGFR Pathway
Cetuximab is a chimeric (mouse/human) monoclonal antibody that was developed with a high affinity for the extracellular domain of EGFR.37 When bound it inhibits EGFR downstream pathways. It was first approved in 2006 and is currently the only Food and Drug Administration-approved targeted therapy for HSNCC. There are four Phase III clinical trials that have evaluated the effectiveness of cetuximab as combination therapy with either radiation or platinum-based treatments in locoregionally advanced, recurrent, and/or metastatic disease (Table 1.2).3841 In advanced disease cetuximab demonstrated nearly 3 months of survival benefit when combined with conventional chemotherapy. Its major side effect is an acne-like rash that is not usually debilitating. Interestingly, the severity of the rash may indicate the extent of cetuximab effectiveness.42 Unfortunately, while amplification of EGFR correlates with poor prognosis, it does not correspond to response to cetuximab. In addition resistance to cetuximab, either intrinsic or acquired, is common and limits its overall effectiveness.
A number of mechanisms have been proposed to explain cetuximab resistance.43 A mutant variant of truncated EGFR called EGFRvIII, estimated to be present in 40% of tumors, is constitutively active and lacks the extracellular domain where cetuximab binds.23
8
Table 1.2   Phase III clinical trials evaluating the efficacy of cetuximab (Erbitux)
Study
Study population
Study design
Intervention
Results
Critique
Burtness, et al.38
117 enrolled patients with metastatic or recurrent HNSCC (60 patients received cetuximab)
Randomized placebo controlled trial
Cisplatin ± cetuximab
Significant RR with the addition of cetuximab; however, no improvement in PFS or OS
Underpowered to detect less than a 50% difference in PFS or OS
Bonner, et al.39
424 enrolled patients with locoregionally advanced (stage III/ IV) nonmetastatic HNSCC
Randomized multinational study
Radiation ± cetuximab
Significant improvement in locoregional control, PFS and OS at 3 years
No placebo group
Unknown HPV status
Vermorken, et al.40
442 patients with recurrent or metastatic HNSCC
Randomized study
Platinum-5 FU ± cetuximab (extreme trial)
Significantly prolonged OS by 3 months. Two month PFS and 15% increase in RR
No placebo group
Unknown HPV status
Bonner, et al.42
5-year survival update on 2006 Bonner trial
Randomized multinational study
Radiation ± cetuximab
Persistent at 5 years of significant improvement in overall survival
No placebo group
Unknown HPV status
Ang, et al.41
891 patients with locoregionally advanced (stage III/ IV) nonmetastatic HNSCC
Randomized
Radiation and cisplatin ± cetuximab
Triple therapy showed no improvement in PFS or OS; however, there was an increase in mucositis and skin reaction
25% of patients did not receive more than 5 weeks of cetuximab
Possible over-representation of HPV+ patients
(HNSCC: Head and neck squamous cell carcinoma; HPV: Human papilloma virus; OS: Overall survival; PFS: Progression free survival; RR: Response rate).
Small molecule tyrosine kinase inhibitors that can bind the intracellular domain, including erlotinib, gefitinib, were initially posited as a method of overcoming this mechanism of cetuximab resistance; however, phase II and phase III trials of erlotinib and gefitinib have not been promising.44,45 A pilot study with a humanized monoclonal antibody (ABT-806) specifically targeting EGFRvIII, and activated EGFR has recently been reported (Table 1.3).46 In this study of solid tumors, at least two patients had HNSCC and exhibited stable disease for more than 2 months; one had stable disease for nearly six months. A second potential mechanism of cetuximab resistance relates to its ability to heterodimerize with other members of the HER family and cross-activation with other receptor tyrosine kinases (RTKs) like the hepatocyte growth factor receptor (gene is called MET). MET has been shown to be amplified or mutated in a small subset of HNSCC. There are several small molecule inhibitors of MET, including foretinib and crizotinib, that nonselectively inhibits MET as well as VEGF2 and may benefit patients harboring the mutation.43 A recent study demonstrated that single-agent foretinib was well tolerated by 14 patients with recurrent/metastatic HNSCC, and 93% (13/14 patients) had stable disease or tumor shrinkage that was sustained for 13 months.47
 
Target: PI3CA-AKT-mTOR Pathways
One of the challenges of treating HNSCC is that the majority of mutations associated with this disease are inactivating mutations or LOH of tumor suppressor genes. This makes targeted therapies of inactivated genes difficult since there are currently no drugs currently available that restore intrinsic function. Activating mutations seen in PIK3CA and mTOR are some of the few oncogenes and are therefore active areas for drug development. There are a number of multikinase inhibitors including the first PI3K/mTOR inhibitor, BEZ235 currently in early phase I/II clinical trials.24 Inhibitors of mTOR, including everolimus, rapamycin, and temsirolimus, are also under investigation in both preclinical models and early clinical trials. Early results are encouraging.
9
Table 1.3   Targeted therapies in development for head and neck squamous cell carcinoma
Target
Chemotherapeutic
Drug class/effect
EGFR (HER1)
Cetuximab (Erbitux)
Chimeric monoclonal antibody (MAb)
Matuzumab
Nimotuzumab
Panitumumab
Pertuzumab
Specifically inhibits HER2 dimerization with other HER family members
Zalutumumab
Erlotinib
Tyrosine kinase inhibitors (TKIs)
Gefitinib
Afatinib
Dacomitinib
Lapatinib
Vandetanib
EGFRvIII
ABT-806
Specifically binds activated EGFR and EGFRvIII
PI3K-AKT-mTOR
Everolmus
Multikinase inhibitor (MKI)
NVP-BEZ235
Rapamycin
Temsirolimus
(EGFR: Epidermal growth factor receptor; HNSCC: Head and neck squamous all carcinoma).
A phase I trial of 18 patients with locally and/or regionally advanced HNSCC treated with everolimus (in addition to cisplatin and docetaxel) as induction chemotherapy was just recently published.48 In addition to establishing a safe dose for phase II trials, progression-free survival of 87.5% and 77% was reported at 1 and 2 years, respectively. A note of caution: this is also an area of rapid change as evidenced by a phase II trial of temsirolimus and erlotinib that was closed early because of toxicity or death.49
 
CONCLUSION
As head and neck oncologic surgeons, it is increasingly important to understand the molecular mechanisms underlying HNSCC. Here, we have reviewed the critical genes that affect cell replication, differentiation, growth, and death in this malignancy. These alterations lead to dysregulation of signaling pathways in both HPV-negative and HPV-positive HNSCC. Targeted therapies hold great promise in HNSCC by identifying the ideal agent(s) for the correct patient at the appropriate time.
 
ACKNOWLEDGMENT
This work was supported in part by the following grants: NIH P50CA097190 and an American Cancer Society clinical research professorship (To JRG).
REFERENCES
  1. Slaughter DP, Southwick HW, Smejkal W. Field cancerization in oral stratified squamous epithelium; clinical implications of multicentric origin. Cancer. 1953;6(5):963–8.
  1. Califano J, van der Riet P, Westra W, et al. Genetic progression model for head and neck cancer: implications for field cancerization. Cancer Res. 19961;56(11):2488–92.
  1. Leemans CR, Braakhuis BJM, Brakenhoff RH. The molecular biology of head and neck cancer. Nat Rev Cancer 2011;11(1):9–22.
  1. Ha PK, Benoit NE, Yochem R, et al. A transcriptional progression model for head and neck cancer. Clin Cancer Res: an official journal of the American Association for Cancer Research. 2003;9(8):3058–64.
  1. Stransky N, Egloff AM, Tward AD, et al. The mutational landscape of head and neck squamous cell carcinoma. Science. 2011;333:1157–60.10
  1. Agrawal N, Frederick MJ, Pickering CR, et al. Exome sequencing of head and neck squamous cell carcinoma reveals inactivating mutations in NOTCH1. Science (New York, NY). 2011;333(6046):1154–7.
  1. Estilo CL, O-Charoenrat P, Ngai I, et al. The role of novel oncogenes squamous cell carcinoma-related oncogene and phosphatidylinositol 3-kinase p110alpha in squamous cell carcinoma of the oral tongue. Clinical Cancer Res: an official journal of the American Association for Cancer Research. 2003;9(6):2300–6.
  1. Field JK, Pavelic ZP, Spandidos DA, et al. The role of the p53 tumor suppressor gene in squamous cell carcinoma of the head and neck. Arch Otolaryngol-Head Neck Surg. 1993;119(10):1118–22.
  1. Green DR, Kroemer G. Cytoplasmic functions of the tumour suppressor p53. Nature. 2009;458(7242):1127–30.
  1. Somers KD, Merrick MA, Lopez ME, et al. Frequent p53 mutations in head and neck cancer. Cancer Res. 1992;52 (21):5997–6000.
  1. Malumbres M, Barbacid M. Cell cycle, CDKs and cancer: a changing paradigm. Nature Rev. Cancer. 2009;9(3):153–66.
  1. Poeta ML, Manola J, Goldwasser MA, et al. TP53 mutations and survival in squamous-cell carcinoma of the head and neck. New Engl J Med. 2007;357(25):2552–61.
  1. Izzo JG, Papadimitrakopoulou VA, Li XQ, et al. Dysregulated cyclin D1 expression early in head and neck tumorigenesis: in vivo evidence for an association with subsequent gene amplification. Oncogene. 1998;17(18):2313–22.
  1. Michalides RJ, van Veelen NM, Kristel PM, et al. Overexpression of cyclin D1 indicates a poor prognosis in squamous cell carcinoma of the head and neck. Arch Otolaryngol - Head Neck Surg. 1997;123(5):497–502.
  1. Michalides R, van Veelen N, Hart A, et al. Overexpression of cyclin D1 correlates with recurrence in a group of forty-seven operable squamous cell carcinomas of the head and neck. Cancer Res. 1995;55(5):975–8.
  1. Akervall J, Bockmühl U, Petersen I, et al. The gene ratios c-MYC: cyclin-dependent Kinase (CDK) N2A and CCND1: CDKN2A correlate with poor prognosis in squamous cell carcinoma of the head and neck. Clin Cancer Res. 2003; 9:1750–5.
  1. Hynes NE, Lane HA. ERBB receptors and cancer: the complexity of targeted inhibitors. Nature Rev Cancer. 2005;5(5):341–54.
  1. Lin SY, Makino K, Xia W, et al. Nuclear localization of EGF receptor and its potential new role as a transcription factor. Nature Cell Biol. 2001;3(9):802–8.
  1. Loeffler-Ragg J, Witsch-Baumgartner M, Tzankov A, et al. Low incidence of mutations in EGFR kinase domain in Caucasian patients with head and neck squamous cell carcinoma. Eur J Cancer (Oxford, England: 1990). 2006; 42(1):109–11.
  1. Shintani S, Matsuo K, Crohin CC, et al. Intragenic mutation analysis of the human epidermal growth factor receptor (EGFR) gene in malignant human oral keratinocytes. Cancer Res. 1999;59(16):4142–7.
  1. Lee JW, Soung YH, Kim SY, et al. Somatic mutations of EGFR gene in squamous cell carcinoma of the head and neck. Clin Cancer Res: an official journal of the American Association for Cancer Research. 2005;11(8):2879–82.
  1. Grandis JR, Tweardy DJ. Elevated levels of transforming growth factor alpha and epidermal growth factor receptor messenger RNA are early markers of carcinogenesis in head and neck cancer. Cancer Res. 1993;53(15):3579–84.
  1. Sok JC, Coppelli FM, Thomas SM, et al. Mutant epidermal growth factor receptor (EGFRvIII) contributes to head and neck cancer growth and resistance to EGFR targeting. Clinical Cancer Res: an official journal of the American Association for Cancer Research. 2006;12(17):5064–73.
  1. Engelman JA. Targeting PI3K signalling in cancer: opportunities, challenges and limitations. Nat Rev Cancer. 2009;9 (8):550–62.
  1. White RA, Malkoski SP, Wang X-J. TGFβ signaling in head and neck squamous cell carcinoma. Oncogene. 2010;29 (40):5437–46.
  1. Perez-Ordoñez B, Beauchemin M, Jordan RCK. Molecular biology of squamous cell carcinoma of the head and neck. J Clin Pathol. 2006;59(5):445–53.
  1. Pearlstein RP, Benninger MS, Carey TE, et al. Loss of 18q predicts poor survival of patients with squamous cell carcinoma of the head and neck. Genes Chromosomes Cancer. 1998;21(4):333–9.
  1. Bornstein S, White R, Malkoski S, et al. Smad4 loss in mice causes spontaneous head and neck cancer with increased genomic instability and inflammation. J Clin Invest. 2009;119(11):3408–19.
  1. Fukuchi M, Masuda N, Miyazaki T, et al. Decreased Smad4 expression in the transforming growth factor-beta signaling pathway during progression of esophageal squamous cell carcinoma. Cancer. 2002;95(4):737–43.
  1. Natsugoe S, Xiangming C, Matsumoto M, et al. Smad4 and transforming growth factor beta1 expression in patients with squamous cell carcinoma of the esophagus. Clin Cancer Res: an official journal of the American Association for Cancer Research. 2002;8(6):1838–42.
  1. Brakenhoff RH. Cancer. Another NOTCH for cancer. Science (New York, NY). 2011;333(6046):1102–3.
  1. Dotto GP. Notch tumor suppressor function. Oncogene. 2008;27(38):5115–23.
  1. Kurokawa M, Kornbluth S. Caspases and kinases in a death grip. Cell. 2009;138(5):838–54.
  1. Haughey BH, Sinha P. Prognostic factors and survival unique to surgically treated p16+ oropharyngeal cancer. Laryngoscope. 2012;122 Suppl:S13–33.
  1. Maxwell JH, Ferris RL, Gooding W, et al. Extracapsular spread in head and neck carcinoma: impact of site and human papillomavirus status. Cancer. 2013;119:3302–8.
  1. Moody CA, Laimins LA. Human papillomavirus oncoproteins: pathways to transformation. Nat Rev Cancer. 2010; 10(8):550–60.
  1. Goldstein NI, Prewett M, Zuklys K, et al. Biological efficacy of a chimeric antibody to the epidermal growth factor receptor in a human tumor xenograft model. Clin Cancer 11Res: an official journal of the American Association for Cancer Research. 1995;1(11):1311–8.
  1. Burtness B, Goldwasser MA, Flood W, et al. Phase III randomized trial of cisplatin plus placebo compared with cisplatin plus cetuximab in metastatic/recurrent head and neck cancer: an Eastern Cooperative Oncology Group study. J Clin Oncol: official journal of the American Society of Clinical Oncology. 2005;23(34):8646–54.
  1. Bonner JA, Harari PM, Giralt J, et al. Radiotherapy plus cetuximab for squamous-cell carcinoma of the head and neck. New Engl J Med. 2006;354(6):567–78.
  1. Vermorken JB, Mesia R, Rivera F, et al. Platinum-based chemotherapy plus cetuximab in head and neck cancer. New Engl J Med. 2008;359(11):1116–27.
  1. Ang KK, Zhang QE, Rosenthal DI, et al. A Randomized phase III trial of concurrent accelerated radiation plus cisplatin with or without cetuximab for stage III to IV head and neck carcinoma: RTOG 0522. J Clin Oncol. 2014;32(27).
  1. Bonner JA, Harari PM, Giralt J, et al. Radiotherapy plus cetuximab for locoregionally advanced head and neck cancer: 5-year survival data from a phase 3 randomised trial, and relation between cetuximab-induced rash and survival. Lancet Oncol. 2010;11(1):21–8.
  1. Bauman JE, Michel LS, Chung CH. New promising molecular targets in head and neck squamous cell carcinoma. Curr Opin Oncol. 2012;24(3):235–42.
  1. Martins RG, Parvathaneni U, Bauman JE, et al. Cisplatin and radiotherapy with or without erlotinib in locally advanced squamous cell carcinoma of the head and neck: a randomized phase II trial. J Clin Oncol: official journal of the American Society of Clinical Oncology. 2013;31:1415–21.
  1. Argiris A, Ghebremichael M, Gilbert J, et al. Phase III randomized, placebo-controlled trial of docetaxel with or without gefitinib in recurrent or metastatic head and neck cancer: an eastern cooperative oncology group trial. J Clin Oncol: official journal of the American Society of Clinical Oncology. 2013;31(11):1405–14.
  1. Cleary JM, Yee LK-C, Azad N, et al. Abstract 2506: a phase 1 study of ABT-806, a humanized recombinant anti-EGFR monoclonal antibody, in patients with advanced solid tumors. Cancer Res. 2012;72(8 Suppl):2506–6.
  1. Seiwert T, Sarantopoulos J, Kallender H, et al. Phase II trial of single-agent foretinib (GSK1363089) in patients with recurrent or metastatic squamous cell carcinoma of the head and neck. Invest New Drugs. 2013;31(2):417–24.
  1. Fury MG, Sherman E, Ho AL, et al. A phase 1 study of everolimus plus docetaxel plus cisplatin as induction chemotherapy for patients with locally and/or regionally advanced head and neck cancer. Cancer. 2013;119(10):1823–31.
  1. Bauman JE, Arias-Pulido H, Lee S-J, et al. A phase II study of temsirolimus and erlotinib in patients with recurrent and/or metastatic, platinum-refractory head and neck squamous cell carcinoma. Oral Oncol. 2013;49(5):461–7.