Skin Cancer: Squamous Cell Carcinoma

  • Basics

    Squamous cell carcinoma is a common skin cancer that usually appears on sun-exposed areas of the body. In the vast majority of cases it is completely curable. Skin cancer is the most common cancer in the US. Squamous cell carcinoma (SCC) is the second most common skin cancer, following basal cell carcinoma. It can occur on all areas of the body, including the mucous membranes in the mouth and genitals; however, it most commonly arises on sun-exposed areas such as the face, arms, ears, hands, lips, neck, and scalp. More and more people develop skin cancer every year, possibly due to more people living longer, as well as greater populations residing in the sun belt.

    The cancer develops in the outer layer of the skin (epidermis) in cells called squamous cells. Squamous cell carcinoma usually remains confined to the upper skin layers for some time, where it is relatively harmless. It can, however, penetrate deeper into the skin and occasionally spread (metastasize) to distant tissues and organs, significantly reducing the chance of a cure.

    When squamous cell cancer is left untreated, it can expand laterally along the skin surface, penetrate deeper into the middle portion of the skin (the dermis), or grow along nerves or blood vessels. In some instances, SCC can spread to distant organs and tissues in the body via the lymphatic, nerve, or circulatory systems. Large SCCs; those on ears, lips, genitals, or backs of hands; and those that have developed over a prolonged period of time, have a greater risk of metastasis. While localized SCC can usually be easily removed, it is much harder to cure once it has spread in this fashion..

    Experts believe that cumulative sun exposure over the years is the most likely cause for SCC, with an estimated 80% of lifetime exposure obtained before the age of 18.

  • Causes

    SCC develops from the squamous cells of the epidermis Figure 01 [Table 1]. A series of increasingly abnormal changes can develop in the skin’s squamous cells. These changes occur when the cell’s DNA becomes altered (mutated). Subsequent generations of cells that grow from these damaged cells are then damaged themselves. Cell-damaging DNA mutations are usually the result of excessive exposure to sunlight. Other risk factors include radiation, arsenic exposure, burns, and chronic wounds.

    Click to enlarge: Anatomy of the skin

    Figure 01. Anatomy of the skin

    The most common culprit for SCC is sun exposure, or more specifically, ultraviolet (UV) radiation. Damaging ultraviolet radiation occurs in two types: ultraviolet A (UVA) and ultraviolet B (UVB). UVB is the type of radiation primarily responsible for sunburn, and mainly affects the outer skin layers. UVA penetrates more deeply. Both have been implicated in the development of skin cancer.

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