Renal sarcoma is a rare type of cancer that forms in the kidney’s soft tissue, the connective tissue that surrounds the kidneys or the fat around the kidneys. Fewer than 1 percent of kidney cancers are renal sarcomas, according to the American Cancer Society (ACS). Changes to the DNA that makes up the genes inside each of your cells may result in cancer, including renal sarcoma. Usually, DNA mutations that contribute to cancer impair the functioning of your oncogenes (which are the genes responsible for cell division and life) and/or your tumor suppressor genes (which help to keep cell division in check).