Atypical lipomatous tumour (ALT) also known as atypical lipoma is a type of soft tissue tumour that arises from adipose (fat) tissue.

These tumours are characterized by their resemblance to normal fat cells but with some atypical features when examined under a microscope. Atypical lipomatous tumours are typically slow-growing and may not display invasive behaviour, but they have the potential for local recurrence and, in some cases, progression to higher-grade liposarcoma.

Management of atypical lipomatous tumours usually involves surgical removal of the tumour. Monitoring and follow-up care may be recommended to detect any signs of recurrence or transformation into liposarcoma. Treatment decisions are typically based on the location, size, grade, and spread of the tumour, as well as individual patient factors.