Squamous cell carcinoma on a patient's buttocks. This form of skin cancer arises from squamous cells, flat scale-like cells in the upper layers of the skin. The tumour forms interconnecting bands of keratinised cells that invade the surrounding tissue. Squamous cell carcinoma is the second most common form of skin cancer and mostly affects the elderly. This case is a complication of hidradenitis suppurativa, which is caused by the blockage of the apocrine glands typically found in the armpits, buttocks, groin and back. Treatment is with surgical removal of the tumour, combined with radiation therapy and chemotherapy.