Basal cell tumours are the most common skin tumour in cats, arising from the basal cells of the epidermis — the deepest layer of the outer skin. The vast majority (over 90%) are benign and present as solitary, slow-growing, well-defined lumps, often on the head, neck, or shoulders. They are typically darkly pigmented and feel firm to the touch. Benign basal cell tumours are cured by straightforward surgical excision and rarely recur. The uncommon malignant variant (basal cell carcinoma) can invade locally but distant metastasis is rare. Long-haired cat breeds may be somewhat predisposed. Because of their excellent prognosis, these tumours are among the least concerning skin growths a cat owner may encounter, though any new or changing lump should always be evaluated by a veterinarian.