MODEL RELEASED. Hyperkeratosis after skin cancer radiotherapy to treat a basal cell carcinoma on the skin of an 82-year-old woman. Basal cell carcinoma is one of the most common forms of skin cancer, and is most often caused by over-exposure to sunlight. The cancer starts as a small flat nodule and grows slowly, eventually breaking down at the centre to form a shallow ulcer that persistently bleeds. Basal cell carcinomas rarely spread to other parts of the body. This is a nodular form of the disease. Treatment involves the surgical removal of the tumour or radiotherapy. The radiotherapy caused scarring that led to the hyperkeratosis (skin thickening) seen here.