General: malignancy arising from basal cells of the epidermis, four subtypes (nodular, pigmented, superficial, scarring), most common form of cancer


Pathogenesis: cell in the basal layer of epidermis undergoes mutation causing unregulated growth, can be from insult (UV radiation, arsenic), genetic and involves the hedgehog pathway 


HPI: new growth that bleeds, history of skin cancer


Risk factors: sun exposure (geographic location, occupation), light skin pigmentation, lesions on nose or ear have high recurrence rate 


Physical exam: sun-damaged skin (freckles, wrinkles) in sun-exposed areas (head, neck), nodular type, most common,  presents as pearly, partially translucent papule/nodule with telangiectasia, waxy borders, and a central indention, often on the nose, pigmented type presents as a speckled, blue-black papule/nodule with a pearly margin, superficial type presents as a red, scaling, well-defined patch on the chest, often resembles eczema, can have a depressed center, pearly border, scarring type, most aggressive, presents as a white plaque resembling a scar with some crusting or erosion


Differential: sebaceous hyperplasia (yellow, central pore), nevus, seborrheic keratosis, melanoma, squamous cell carcinoma, dermatitis, look for non-healing and rolled borders, if there's doubt biopsy it!


Histology: uniform, blue-nucleus cells creating a thickened epidermal basal layer with involvement or budding into to the upper dermis


Complications: can become disfiguring, rarely metastasizes 


Treatment: (1) reduce sunlight exposure (hats, long-sleeves, SPF 30 sunscreen, avoid mid-day sun), (2) excision, (3) electrodessication and curettage, (4) Mohs, could also try radiation, cryotherapy, topicals like 5-FU


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK