64. Epithelial tumours of the skin

From greek.doctor

Benign epithelial lesions

Seborrheic keratosis is a benign neoplasm of squamous cells which mostly affects the elderly. It is a round, exophytic plaque that are classically described as if they were “stuck on” the skin. Histology shows papillomatosis (hyperplasia of the dermal papillae), Hyperkeratosis and keratin-filled cysts. They’re not associated with sun exposure. The sudden onset of many seborrheic keratoses is called Leser-Trélat sign and is a paraneoplastic syndrome of GI tract cancers. These cancers sometimes produce epidermal growth factors which stimulate the growth of these neoplasms.

Acanthosis nigricans is a darkening of the skin with epidermal hyperplasia. This makes the skin feel more velvet-like. It’s associated with insulin resistance and cancer. It most frequently occurs in the groin.

Actinic keratosis is a sun exposure-related precancerous lesion of squamous cell carcinoma. These plaques are brown or red in colour and have a sandpaper-like touch. They mostly arise on areas exposed to the sun like face, neck and arms. Around 10% of actinic keratoses progress into SCC. Microscopically lower portion of epidermis show cytologic atypia, often with hyperplasia of basal cells or with atrophy and diffuse thinning of epidermis. Actinic keratosis also show hyperkeratosis, parakeratosis and dermal solar elastosis. Dermal solar elastosis are thickened blue-grey elastic fibers as a result of chronic sun damage.

Basal cell carcinoma

Basal cell carcinoma is a malignant proliferation of basal cells of the epidermis. It’s the most common type of skin cancer, but it’s not the most lethal one. Like melanoma it’s associated with UV radiation-mediated DNA damage.

Risk factors:

  • Excessive exposure to UV radiation (much sun, little sunscreen)
  • Light skin
  • Dysplastic nevus syndrome
  • Albinism
  • Xeroderma pigmentosum

Morphology: Basal cell carcinoma often produces a nodular lesion with ulceration in the centre, which forms a crater. The nodule classically have a “pearly” appearance and is often surrounded by telangiectasia. It mostly affects sun-exposed parts of the body, like the face and arms. Skin cancer on the upper lip is typically basal cell carcinoma.

Pathogenesis: Dysregulation of the Hedgehog signalling pathway, which you might remember from embryology, is typical for basal cell carcinoma.

Treatment and prognosis: This type of cancer grows slowly and virtually never metastasizes, so excision is curative in most cases.

Squamous cell carcinoma

Squamous cell carcinoma (SCC) is a malignant proliferation of keratinocytes in the epidermis. It’s the second most common skin cancer after basal cell carcinoma. The risk factors are the same as for melanoma and basal cell carcinoma, plus some extra. Squamous cell carcinoma of the skin is much less aggressive than squamous cell carcinoma at mucosal sites.

Risk factors:

  • Excessive exposure to UV radiation (much sun, little sunscreen)
  • Light skin
  • Dysplastic nevus syndrome
  • Albinism
  • Xeroderma pigmentosum
  • Immunosuppression
  • Arsenic poisoning
  • Chronic inflammation of the skin
  • Skin burns

Morphology: SCC forms an ulcerated mass that typically occurs on the face, especially on the lower lip.

Treatment and prognosis: SCC grows slowly and rarely metastasizes. Excision is usually curative.