Usually the lumps seen in limb muscle may be sarcomas,which may be noncancerous or cancerous when they are growing in size. the first symptom of soft tissue sarcoma is a painless slow-growing lump in the trunk or limbs. As the mass grows, it may begin to press upon nerves or muscles and possibly cause pain, numbness, and/or skin breakdown.when it was small may be your dr thought of lipoma which requires no treatment when asyptomatic,but now you are referred to surgeon as it is drastically increasing in size to r/o sarcoma. biopsy of lump tissue, MRI,CT,bone scans are required to confirm the sarcoma as well as its spread to bones and the stage of the disease. If it is cancerous sarcoma excision of lump and chemo and radiotherapy are required.any how you keep your mind positive and maintain diet and exercise and consult your surgeon.hope your lump is benign one.