page_title: Skin cancer
section_title: Pathophysiology
hierarchical_section_title: Skin cancer / Pathophysiology
caption_attribution_description: English: Micrograph of malignant melanoma. Cytology specimen. Field stain. The micrograph shows features commonly seen in melanoma: Large (&gt;2x the size of a RBC), dyscohesive cells. Epithelioid binucleated single cells, "bug-eyed monster cells". Cells with: Large nucleoli. Abundant granular cytoplasm. Features associated with melanoma but not seen: Pigment. Pseudoinclusions. Singular spindle cells.
context_page_description: Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer, squamous-cell skin cancer and melanoma. The first two, along with a number of less common skin cancers, are known as nonmelanoma skin cancer. Basal-cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or result in death. It often appears as a painless raised area of skin that may be shiny with small blood vessels running over it or may present as a raised area with an ulcer. Squamous-cell skin cancer is more likely to spread. It usually presents as a hard lump with a scaly top but may also form an ulcer. Melanomas are the most aggressive. Signs include a mole that has changed in size, shape, color, has irregular edges, has more than one color, is itchy or bleeds.
  More than 90% of cases are caused by exposure to ultraviolet radiation from the Sun. This exposure increases the risk of all three main types of skin cancer. Exposure has increased, partly due to a thinner ozone layer.
context_section_description: A malignant epithelial tumor that primarily originates in the epidermis, in squamous mucosa or in areas of squamous metaplasia is referred to as a squamous-cell carcinoma.
  Macroscopically, the tumor is often elevated, fungating, or may be ulcerated with irregular borders. Microscopically, tumor cells destroy the basement membrane and form sheets or compact masses which invade the subjacent connective tissue (dermis). In well differentiated carcinomas, tumor cells are pleomorphic/atypical, but resembling normal keratinocytes from prickle layer (large, polygonal, with abundant eosinophilic (pink) cytoplasm and central nucleus).
  Their disposal tends to be similar to that of normal epidermis: immature/basal cells at the periphery, becoming more mature to the centre of the tumor masses. Tumor cells transform into keratinized squamous cells and form round nodules with concentric, laminated layers, called "cell nests" or "epithelial/keratinous pearls". The surrounding stroma is reduced and contains inflammatory infiltrate (lymphocytes). Poorly differentiated squamous carcinomas contain more pleomorphic cells and no keratinization.
  A molecular factor involved in the disease process is mutation in gene PTCH1 that plays an important role in the Sonic hedgehog signaling pathway.
caption: Micrograph of melanoma, fine-needle aspiration (FNA), field stain
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