Skin Squamous Cell Carcinoma

Overview
  • Squamous Cell Carcinoma (SCC) of the skin is malignant neoplasm of the keratinocyte and represents the second most common cutaneous malignancy. The primary risk factor for SCC is life-long sun exposure. SCCs are locally invasive and a small proportion can metastasize.
Pathogenesis
  • SCCs are related to life-long sun exposure in susceptible populations, especially those with fair skin. Consequently, SCCs tend to occur in sun-exposed areas, and have a predilection for the lower half of the face, below the lips. The relationship between SCCs and actinic keratoses (AK) is somewhat unclear. SCCs do not always arise from the context of an AK, and few AKs progress to SCCs.
  • The risk of SCC development is increased in immunocompromised patients, suggesting immune surveillance is important for keeping these tumors under control. SCCs can also arise in areas of chronic irritation or injury such as burn scars and sinus tracts associated with draining osteomyelitis.
Morphology
  • Gross Morphology
    • SCCs display a variety of morphologies but are often firm, well-demarcated papules, plaques or nodules with an erythematous or flesh color. They may display scale and crust or be highly ulcerating.
  • Histological Morphology
    • SCCs are characterized by keratinocyte atypia. When this atypia occurs at all levels of the epidermis but atypical cells have not crossed the basement membrane then this is referred to as "Squamous Cell Carinoma in situ" or "Bowen's Disease". Recall that actinic keratosis is defined as cellular atypia only in the lower levels of the epidermis.
    • When atypical keratinocytes invade into the dermis then bonafide SCC is achieved. SCC cells may invade into the dermis as tongues or cords, or begin to separate off into individual cells. Depending on the tumor, cells may be well-differentiated and retain keratinization, observed as small "keratin pearls" within the dermis, while in other tumors SCC cells may be highly anaplastic and display no keratinization.
Clinical Consequences
  • As mentioned, SCCs are malignant and can be highly invasive. A small proportion of SCCs (less than 5%) may metastasize.
Treatment
  • If SCCs remain localized, they can be successfully treated by surgical excision.