SKIN NEOPLASMS

Benign

Seborrheic Keratosis - benign keratinocyte proliferation. Flat greasy moles with keratin pits. It’s so well-demarcated, that it looks like you can peel it off (stuck-on appearance). On Histo, it contains balls of Keratin (pseudocyst). Fairly common, they are nothing to worry about. 

Leser-Trelat Sign - explosive onset of many Seborrheic Keratoses, suggesting an abdominal cancer

Acanthosis Nigricans - benign epidermal hyperplasia.  Velvet darkening of skin folds (eg, neck, axilla). Associated with insulin resistance or cancer (if the onset is explosive). 

Worrisome

Actinic Keratosis - precursor to SCC. Caused by UV-B light. This is “lots of keratin” disease. The lesions are especially flaky. They start out as sandpapery discolorations, but progress to scaly papules (and eventually horns!). Hyperkeratotic/parakeratotic on histology. 

Malignant

Basal Cell Carcinoma - malignant basal cells. Most common skin cancer. Caused by exposure to UV-B light (eg, tanning, albinism, xeroderma pigmentosum). Elevated nodule with a central ulcer, rolled pearly borders and full of dilated vessels (telangiectasias). Classically on the upper lip, but these can appear anywhere the sun shines. Treat with surgical excision. Metastasis is rare. 

Squamous Cell Carcinoma - malignant skin cells. 2nd most common skin cancer. Also caused by exposure to UV-B light. Additionally, it’s caused by immunosuppressive therapy (transplants), arsenic poisoning and chronic inflammation (burn injury scar). It’s an ulcerated nodular mass (classically involving the LOWER lip). Treat with surgical excision. Metastasis is pretty uncommon. 

Keratoacanthoma - a well-differentiated variant of SCC. It appears and disappears without warning. Looks like a cup-shaped tumor filled with keratin debris. Lower yield.

Xeroderma Pigmentosum - genetic defect in nucleotide excision repair → UV damage DNA dimers can’t be fixed → frequent skin cancer