Color Atlas of Oral Cancer KMK Masthan, N Aravindha Babu, Vidyarani Shyamsundar
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IntroductionChapter 1

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Word “cancer” derived from the Latin word “karkinos”,which means crab. It is explained so because of the nature of cancerous cells which adhere to any part that they size upon in an obstinate manner like a crab. Malignant neoplasms are a broad group of diseases involving unregulated cell growth. All the malignant tumours are collectively called as cancer.
Oral cancer is a heterogeneous group of diseases arising from different parts of the oral cavity such as lip, tongue and gingiva, floor of the mouth, buccal mucosa, palate and the retromolar trigone. It is the 6th most common cancer worldwide. In India, it ranks among top three of all cancers.
The oral cancer includes several types of cancers in the oral cavity such as oral squamous cell carcinoma, malignant salivary gland tumours, melanoma, basal cell carcinoma etc. Oral squamous cell carcinoma (OSCC) constitutes to over 90% of all cancers in oral region. The word Oral cancer is used almost synonymous to oral squamous cell carcinoma.
The development of majority of OSCC appears to be due to chronic exposure to topical carcinogens, specially tobacco (smoked and smokeless), aracanut and alcohol. Carcinogenic substances alters genetic configuration of oral epithelial cells. As a result, normal oral epithelium gets converted into potentially malignant (dysplastic) lesions and subsequently to the invasive Oral squamous cell carcinoma (OSCC).
Cancer begins with multiple cumulative epigenetic and genetic alterations that sequentially transform a cell or a group of cells in a particular organ. The early genetic events might lead to clonal expansion of pre-neoplastic daughter cells in a particular tumour field. Subsequent genomic changes in some of these cells drive them towards the malignant phenotype. These transformed cells are diagnosed histopathologically as cancers owing to changes in cell morphology. Conceivably, a population of daughter cells with early genetic changes (without histopathology) remain in the organ, responsible for field cancerization. It is also noted that about 50% of oral squamous cell carcinomas arise from apparently normal appearing oral mucosa clinically.
There are multiple modifications in the physiology of cancer cell, such as unlimited replicative potential, self sufficiency of growth signals, insensitivity to growth inhibitor signals, evasion of apoptosis, ability to promote sustained angiogenesis, and capacity to invade surrounding tissue and metastasize.
Currently, numerous newer instruments for screening and advanced diagnostic aids are available. But still the histopathological diagnosis following the biopsy is the gold standard in the diagnosis of potentially malignant disorders and malignancy.
Even though numerous markers are available currently, none of the available molecular markers have proved to be of diagnostic or prognostically significant. All these lesions can be easily visualised. Early diagnosis and prevention of malignant transformation of potentially malignant lesions are the best way to improve the prognosis. The knowledge about the screening, the clinical appearance and management among health care providers is very important.