Lump in the Side or Lower Back
The kidneys are located at the lower sides of the back or abdomen. Some people with kidney cancers may notice a slight bulge under the skin of their abdomen, sides, or lower back. This is due to the development of cancerous tumors on the kidneys. The cancerous mass usually feels hard, although many people may not notice it in the early stages.
Not all abdominal lumps are a sign of kidney cancer. While they may be caused by cancers, there are many organs in the abdomen where cancerous masses can form besides the kidney. Abdominal lumps develop in around 45 percent [3] of people with renal cell carcinoma. The lumps may or may not be externally observable. You should see a doctor if you notice a hard mass anywhere on your torso.