@anaxibarra: Replying to @Brittany hopefully this explains things better, if it’s clumping / you can physically feel it and you notice it growing then probably talk to your doctor. Liposacroma is a rare type of cancer that can form in fat cells in the arms and legs. It's a type of sarcoma, which is a cancer that starts in soft tissues like fat, muscles, and tendons. Symptoms of liposarcoma in the arm include: A growing lump under the skin, Pain, Swelling, and Weakness in the affected limb