<s>[INST] My friend has a lump in her thigh on the backside. It is not on the surface. It is at least the size of a walnut. She discovered this when she lost a significant amount of weight and was able to feel it more easily. She says it does not hurt. Any ideas? [/INST] hi.noted history of non-painful lump on the patient's posterior thigh. it may be a case of lipoma (fatty deposit), fibroma (fibrous tissue formation) or a cystic formation. other lesion types such as malignancy must also be ruled-out. it is best if you bring your friend to a doctor, preferably a general surgeon, especially if the lesion is bothering her. diagnostics and management (medical and/or surgical) will be directed accordingly. definitive management is surgical excision of the lesion with proper antibiotic regimen and daily wound care thereafter.hope this helps.good day!!~dr.kaye </s>