Sarcoma cells. Coloured scanning electron micrograph (SEM) of sarcoma cells spreading (metastasising). Sarcomas are cancers of the connective tissues, which include muscles, blood vessels, nerves and fat. The flattened processes on the edges of the cells allow them to move to other parts of the body. The movement of cancer cells around the body is an important part of a cancer's malignancy. Sarcomas are a rare type of cancer and are often hard to detect.