Fibromas are tumors of the fibrous tissue on, in or surrounding the kidney. They are rare and most often found in women. Their cause is unknown. Usually they grow on the periphery of the kidney and can become large before becoming clinically obvious. Most are asymptomatic. While generally benign, these tumors have no special characteristics to differentiate them from other, malignant tumors of the kidney. Because of this uncertainty of diagnosis, most physicians treat them surgically. Partial or radical nephrectomy is the standard approach.
As noted, the tumors that characterize RCC are made up of malignant (cancerous) cells that grow together in a mass. If imaging or other procedures detect the presence of a tumor, a cell sample may be taken for microscopic examination. In general, physicians avoid performing needle biopsies of suspected kidney tumors because of the risk of causing bleeding or other complications. However, in some cases the tumor may contain a fluid-filled cyst. By puncturing the cyst with a fine needle, a small amount of this fluid can be drawn out for examination by a pathologist, who will look for cancer cells. This can help determine the type of cancer a patient has, and aid the physician in recommending an
appropriate form of treatment. While no longer common, a similar technique can be employed to collect a sample of solid tissue from a noncystic tumor. 