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What is Squamous cell carcinoma and explain in detail?
Squamous-cell carcinomas (SCCs),  also known as epidermoid carcinomas, comprise a number of different types of cancer that begin in squamous cells. These cells form on the surface of the skin, on the lining of hollow organs in the body, and on the lining of the respiratory and digestive tracts.Common types include:

Squamous-cell skin cancer: A type of skin cancer
Squamous-cell carcinoma of the lung: A type of lung cancer
Squamous-cell thyroid carcinoma: A type of thyroid cancer
Esophageal squamous-cell carcinoma: A type of esophageal cancer
Squamous-cell carcinoma of the vagina: A type of vaginal cancerDespite sharing the name "squamous-cell carcinoma", the SCCs of different body sites can show differences in their presented symptoms, natural history, prognosis, and response to treatment.

By body location
Human papillomavirus infection has been associated with SCCs of the oropharynx, lung, fingers, and anogenital region.

Head and neck cancer
About 90% of cases of head and neck cancer (cancer of the mouth, nasal cavity, nasopharynx, throat and associated structures) are due to SCC.

Skin
Squamous cell carcinoma of the skin is the second most common skin cancer, accounting for over 1 million cases in the United States each year.

Thyroid
Primary squamous-cell thyroid carcinoma shows an aggressive biological phenotype resulting in poor prognosis for patients.

Esophagus
Esophageal cancer may be due to either esophageal squamous cell carcinoma (ESCC) or adenocarcinoma (EAC). SCCs tend to occur closer to the mouth, while adenocarcinomas occur closer to the stomach. Dysphagia (difficulty swallowing, solids worse than liquids) and painful swallowing are common initial symptoms. If the disease is localized, surgical removal of the affected esophagus may offer the possibility of a cure. If the disease has spread, chemotherapy and radiotherapy are commonly used.

Lung
When associated with the lung, it is typically a centrally located large-cell cancer (nonsmall-cell lung cancer). It often has a paraneoplastic syndrome causing ectopic production of parathyroid hormone-related protein, resulting in hypercalcemia, but paraneoplastic syndrome is more commonly associated with small-cell lung cancer. It is primarily due to smoking.

Penis
Human papillomavirus (HPV), primarily HPV 16 and 18, are strongly implicated in the development of SCC of the penis.
Three carcinomas in situ are associated with SCCs of the penis:
Bowens disease presents as leukoplakia on the shaft.  Around a third of cases progress to SCC.
Erythroplasia of Queyrat, a variation of Bowens disease, presents as erythroplakia on the glans.
Bowenoid papulosis, which histologically resembles Bowen disease,  presents as reddish papules.

Prostate
When associated with the prostate, squamous-cell carcinoma is very aggressive in nature. It is difficult to detect as no increase in prostate-specific antigen levels is seen, meaning that the cancer is often diagnosed at an advanced stage.

Vagina and cervix
Vaginal SCC spreads slowly and usually stays near the vagina, but may spread to the lungs and liver. This is the most common type of vaginal cancer.

Bladder
Most bladder cancer is transitional cell, but bladder cancer associated with schistosomiasis is often SCC.

Diagnosis
Medical history, physical examination and medical imaging may suggest a squamous cell carcinoma, but a biopsy for histopathology generally establishes the diagnosis. TP63 staining is the main histological marker for Squamous cell carcinoma. In addition, TP63 is an essential transcription factor to establish squamous cell identity.

Classification
Cancer can be considered a very large and exceptionally heterogeneous family of malignant diseases, with squamous cell carcinomas comprising one of the largest subsets. All SCC lesions are thought to begin via the repeated, uncontrolled division of cancer stem cells of epithelial lineage or characteristics. SCCs arise from squamous cells, which are flat cells that line many areas of the body. Some of which are keratinocytes. Accumulation of these cancer cells causes a microscopic focus of abnormal cells that are, at least initially, locally confined within the specific tissue in which the progenitor cell resided. This condition is called squamous cell carcinoma in situ, and it is diagnosed when the tumor has not yet penetrated the basement membrane or other delimiting structure to invade adjacent tissues