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Could my kidney cysts be cancerous?

Asked by Benjamin, New York

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I have a cyst in each of my kidneys. Can this be cancerous?

Expert Bio Picture

Conditions Expert Dr. Otis Brawley Chief Medical Officer,
American Cancer Society

Expert answer

Dear Benjamin:

Renal cysts occur in a variety of genetic diseases in adults and children, but "simple renal cysts" are commonly observed in normal kidneys. They are so common, it is difficult to consider them a disease. More and more people are being diagnosed with these lesions as we use more medical imaging technology such as ultrasound, X-ray and CT scanning. In one survey of people undergoing ultrasound for evaluation of non-kidney-related problems, 15 percent of men and 7 percent of women aged 50 to 69 had a renal cyst. One-third of men and 15 percent of women older than 70 had a renal cyst.

The initial radiologic appearance of most cysts determines what further evaluation is needed. The physician needs to accurately distinguish simple renal cysts from complex renal cysts. Simple cysts are round and have one wall, much like a ping pong ball. They rarely require treatment. Complex cysts have walls within the outer wall or are a collection of small cysts. The latter can harbor cancerous masses.

Many physicians use the Bosniak classification of renal cysts to determine follow-up. Observation of lesions is far more common than biopsy. Traditionally biopsy required removal and loss of the kidney. Biopsy can now be done with a needle through the skin using CT imaging to guide the needle. These needle biopsies were once discouraged but are now done in very specific circumstances.

Bosniak uses a complicated algorithm of CT scan characteristics such as size, density and perfusion to place cystic renal masses into one of five different categories. Bosniak categories I and II are generally simple cysts and do not require further evaluation. Some would repeat an ultrasound at six to 12 months to assure stability and a correct diagnosis.

Bosniak category IIF cysts are more complex and deserve follow-up imaging to document stability. The absence of change over time supports benign disease, while progression suggests a cancer. In one study with long-term follow-up of 42 patients with category IIF, two eventually developed more complicated cysts that were found to be cancerous. Observation prevented many unnecessary surgeries.

Many recommend that all Bosniak category III lesions undergo surgical removal and evaluation, as 40 percent to 50 percent will be cancer. With this approach, there is still a significant number of unnecessary surgeries. Some recommend close follow-up with magnetic resonance imaging to avoid this. Magnetic resonance imaging is especially useful for characterizing the inside of a cyst that is indeterminate after ultrasound and CT. Serial MRI examinations at three, six and 12 months are warranted in some patients.

There is little debate that category IV lesions require surgical removal of the kidney. Approximately 85 percent to 100 percent of these are cancer.

Greater than 90 percent of those diagnosed with renal cancer still confined to the kidney are alive and disease-free five years after diagnosis. Five year disease free survival is 60 percent to 70 percent for those whose disease has grown outside the kidney. Survival rates are very low if the disease has spread beyond the kidney.

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