A renal tumor is a swelling or lesion in the kidney that occurs due to abnormal cell growth. The kidney is a paired organ in the posterior, or back, of the abdomen that is responsible for urine production, blood filtration, and reabsorption of needed water, salts, and sugars back into the bloodstream, amongst other functions. There are several types of kidney tumors, which may be benign or malignant. If the tumor is benign, it is not cancerous and does not metastasize, or spread, into other tissues and does not grow in an uncontrolled manner. If the tumor is malignant, it becomes progressively worse through abnormal growth and spreading to other tissues via blood, lymph, or direct invasion.
Benign renal tumors include renal adenoma, renal oncocytoma, angiomyolipoma, fibroma, and lipoma. Though renal adenomas are small and benign, they closely resemble malignant renal cell carcinoma (RCC) cells and are widely considered to be precancerous. Like renal adenomas, renal oncocytomas are also considered to be precancerous, resemble RCC cells under the microscope, and usually present no symptoms. Unlike renal adenomas, renal oncocytomas are not unique to the kidney and often become large. To prevent cancer from developing, doctors usually recommend the surgical removal of both renal adenomas and renal oncocytomas if the patient’s overall health permits.
An angiomyolipoma, also called a renal hamartoma, is a benign tumor resulting from a rare genetic mutation that usually occurs in middle-aged women. Though it is not precancerous, a large angiomyolipoma is potentially fatal if it ruptures. If this tumor is large, begins growing, or presents symptoms, doctors will likely recommend surgical removal or an arterial embolization procedure.
A fibroma is another rare benign kidney tumor, more common in women. This tumor is often asymptomatic, occurs on the rim of the kidney, and resembles malignant tumors. Because it is difficult to diagnose whether the tumor is malignant or benign, doctors often recommend surgical removal. Lipomas are also rare and more common in middle-aged women. This tumor affects fat cells in the kidney, may present symptoms of regional pain and blood in the urine, and may be precancerous.
Malignant tumors most commonly result from a cancer called renal cell carcinoma (RCC), which originates in the epithelia of the proximal tubule in the nephron of the kidney. Malignant tumor types are classified based on the appearance of the cancerous cells under the microscope. The four specific types are clear cell renal cell carcinoma, papillary renal carcinoma, chromophobe renal cell carcinoma, collecting duct. RCCs that don’t fit the characteristics of those four types are called unclassified renal carcinomas. Surgical removal with a procedure known as nephrectomy is recommended for all types of RCC when the tumor is limited to the kidney.
Clear cell RCC is by far the most prevalent. The cells of these tumors show up pale or clear under a microscope. Papillary RCC exhibits finger-like projections from the cancerous cells and is subdivided into two groups, type I and type II. Type II has more likelihood of metastasizing. Chromophobe RCC cells resemble clear cell RCCs, but usually metastasize less than clear cell RCC. Collecting duct carcinoma is very rare, very aggressive, and resembles papillary RCC.
Other types of malignant tumors include Wilms’ tumor, transitional cell carcinoma, and renal sarcoma. Wilm’s tumor, also known as nephroblastoma, is a fairly rare tumor that affects young children. This renal tumor may spread to other tissues, but is highly treatable with methods such as surgery, chemotherapy, and radiation.
Transitional cell carcinoma is a kidney cancer that originates in the renal pelvis, where the kidney articulates with the ureter. This tumor is likely caused by cigarette smoking and is treated by nephrectomy, chemotherapy, and radiation. Nephrectomy is the first line of treatment, and usually includes surgical removal of the affected kidney, ureter, and part or all of the bladder.
A renal sarcoma is a rare cancer that affects the connective tissue of the kidney. This renal tumor may present symptoms of blood in the urine, a palpable lump in the abdomen, and lower back pain. If the renal tumor is localized and the patient can withstand surgery, doctors will likely recommend nephrectomy. Chemotherapy and radiation may also be used.