Cystic kidney cancer? A patient's guide to cysts and kidney cancer
Kidney cysts (also called renal cysts) are common and are rarely a sign of kidney cancer. Simple kidney cysts are usually benign and don’t cause problems. However, a complex kidney cyst may indicate cancer.
Cystic renal tumors often resemble cysts in imaging scans, and can share other structural characteristics with kidney cysts. The good news for patients is that these cancers are less likely to metastasize (spread) to other areas of the body and tend to have higher survival rates than other non-cystic subtypes of kidney cancer.
In this guide, you'll learn about the relationship between kidney cysts and cancer, different types of cystic renal tumors, treatments, prognosis, survival, and more, with stories from real patients.
In the Inspire Kidney Cancer Community, members share their personal experiences of living with renal cancer and how to find support. This content should not be used as a substitute for professional medical advice, diagnosis, or treatment. As always, consult with your doctor before trying any new treatments or medications.
Can kidney cysts lead to cancer?
Studies suggest that at least 10% to 20% of adults are living with simple renal cysts, and most of the time, these cysts don't cause any problems. In fact, most people with simple kidney cysts are not aware of them unless a cyst shows up on a routine imaging scan.
On the other hand, complex cysts, which are larger and thicker cysts, are more likely to interfere with kidney function and are sometimes cancerous.
After detecting suspicious cysts, doctors typically use an MRI or CT scan to examine them further. The Bosniak classification system describes cysts according to their size, appearance, and risk of being malignant (cancerous) as follows:
Class I: Also called a simple cyst, the cyst has a hairline thin wall with no calcifications or solid components, with low malignancy risk (about 3%).
Class II: The cyst has few thin dividing walls and little calcification, with about a 6% malignancy risk.
Class IIF ("F" means follow up): The cyst has more than a few minimally thickened walls with thick calcification, and around a 7% risk of malignancy.
Class III: The cyst with thickened, irregular walls and measurable enhancement (a sign that suggests there could be tumor tissue extending past the border of the cyst), approximately 55% of which are malignant.
Class IV: The cyst has clear features of malignancy (cancer), and about a 91% risk of being malignant.
Research into the cancer risk of each category of Bosniak cyst is ongoing. Your medical team may provide you with different risk estimates.
Learn more about the different types of kidney cysts, how they're detected, why they sometimes require removal, the methods doctors use to remove kidney cysts, recovery time, and more.
What size of kidney cyst is dangerous?
For Bosniak class I cysts, patients typically do not need further follow-up or treatment unless symptoms occur. In contrast, Bosniak class II to class IV cysts can require additional testing, follow-up appointments, and, especially in the case of class IV, surgery to remove the tumor tissue.
Also, in some cases, even simple cysts can grow large enough to interfere with kidney function or cause other issues. While not cancerous, they may still require surgical removal for these reasons.
What is polycystic kidney disease and does it increase the risk of kidney cancer?
Polycystic kidney disease (PKD) is a type of disorder that occurs when multiple cysts form on the kidneys, often resulting in enlarged kidneys and reduced kidney function. The most common form is autosomal dominant PKD (or ADPKD), which accounts for 90% of PKD cases. There is a possible association between ADPKD and cancer, but there's also conflicting evidence, and studies are limited at this time. Researchers have also pointed out that ADPKD shares some underlying features with kidney cancer, such as out-of-control growth of renal cells.
Some studies have found a two- or three-fold increased risk of kidney cancer in patients with ADPKD. In the US, clear cell renal cell carcinoma (ccRCC) affects approximately 11 out of 100,000 (0.011%) people per year. Therefore, people with ADPKD may have approximately a 0.02 to 0.03% chance of developing ccRCC annually.
However, other studies have found no relationship between ADPKD and kidney cancer risk.
Finally, some evidence suggests there is a possible link between a rarer form of PKD known as autosomal recessive polycystic kidney disease or ARPKD (also called childhood PKD) and a heightened risk of kidney cancer. Because ARPKD is exceedingly rare and there isn't conclusive data, researchers aren't sure if ARPKD increases kidney cancer risk.
Acquired cystic kidney disease and its relationship to kidney cancer
Acquired cystic kidney disease (ACKD) is a condition that occurs mainly in patients with end-stage renal disease (ESRD), also called kidney failure. Most of these patients receive dialysis, a life-saving treatment that is used in patients whose kidneys aren't working. Up to half of dialysis patients may develop ACKD.
In ACKD, patients develop multiple small cysts in each kidney. Patients with this condition typically have smaller kidneys than usual. Most of the time, ACKD does not cause noticeable symptoms, but it appears to increase the risk of renal cancer.
Some evidence suggests that up to 80% of patients with ACKD may develop renal cancer, particularly a form known as cystic renal cell carcinoma. Overall, except for people with ACKD, cystic renal cell carcinoma is rare and only accounts for 1% to 2% of all kidney cancers.
What is cystic kidney cancer?
Cystic renal cell carcinoma (CRCC) is a type of kidney cancer that is composed entirely of multiple cysts. The septa (chambers) of these cysts contain small groups of clear cells with an identical appearance to clear cell carcinoma. CRCC is an uncommon type of renal cell carcinoma (RCC), accounting for less than 5% of RCC cases.
Cystic renal tumors are tumors located on the kidney that contain both solid and liquid parts. In general, they resemble cysts or share features in common with cysts. Some cystic renal tumors are benign (non-cancerous), while others are malignant (cancerous).
Malignant cystic renal tumors, or cystic kidney cancers, are not a single, specific type of kidney cancer. Rather, there are several different types of kidney cancer that may sometimes — but not always — have a cystic subtype or presentation.
Examples include the following:
cystic clear cell renal cell carcinoma (which may be unilocular or multilocular, having a single chamber or multiple chambers with dividing walls)
cystic collecting duct carcinoma
papillary cystic renal cell carcinoma
mixed epithelial and stromal tumor (MEST)
primary synovial sarcoma of the kidney
tubulocystic carcinoma
The reasons a tumor may have cyst-like characteristics can also vary, including unilocular or multilocular cyst growth that occurs after the development of the tumor, necrosis (tissue death), or the development of cancer cells within the lining of an existing simple cyst.
Learn more about kidney cancer statistics, information on rare types of kidney cancer, the best available treatments for rare kidney cancers, and more, with stories from real patients.
Treatments, prognosis, and survival for cystic kidney cancer
Evidence suggests that in most cases, cystic subtypes of kidney cancer have a much better prognosis, with higher survival rates compared to non-cystic subtypes. For example, one study found that patients with cystic renal cell carcinoma had a five-year disease-free survival rate of 92% and a 10-year disease-free survival rate of 83% to 84%.
While the Bosniak cyst classification system is useful for predicting malignancy (the presence of cancer), as discussed previously, even Bosniak stage IV cysts appear to have favorable outcomes for most patients when treated appropriately.
Many times, cystic renal cell carcinoma can be cured with conservative surgical treatment, particularly resectioning or partial nephrectomy. In some cases, however, nephrectomy (complete kidney removal) or radical nephrectomy (removal of the kidney and surrounding tissues) may be required.
Unlike other types of kidney cancer, because cystic kidney cancers are unlikely to metastasize (spread), immunotherapy and targeted therapies are rarely necessary in these cases.
A nephrectomy is a major surgery that removes some or all tissue from a patient's kidney. The most common reason for a nephrectomy is a tumor, usually caused by kidney cancer that has not metastasized (spread to other parts of the body). Learn more.
Kidney cysts and cancer: Patient stories
Kidney cysts with a low Bosniak grade have a low risk of malignancy but may require follow-up:
"My most recent MRI indicated a Bosniak 2F renal cyst with multiple thin septations (divisions) measuring 3.1 x 2.5 x 2.3 cm . I've been monitoring this for several years with ultrasound, CT and MRI. Its size changes slightly with each new measurement. I think that '2' means a pretty low chance of malignancy, and the 'F' means follow-up recommended." Go to post
"All of my issues started with a 'heavy' feeling in my diaphragm that caused much discomfort in the upper abdomen. I started with an ultrasound which was said to be a cluster of many cysts or a cyst with septations. I was then sent for a CT which proved the cyst to be a complex cyst with septations class llF with a follow up recommended every 6 months." Go to post
When kidney cysts have a high risk of malignancy, or could cause other issues, doctors generally recommend cyst removal surgery:
"I just had a Bosniak level 3 cyst removed about 6 weeks ago. It was found quite by accident and fortunately it was rather small when initially detected. Bosniak 3 cysts have a significant chance of being cancer... I decided to have mine removed (laparoscopically) and I'm glad I did. I was one of the lucky ones, as my cyst turned out to be a benign tumor. Although this tumor wasn't cancerous, it was pressing on the major blood supply to that kidney. If I had waited just a few months the tumor would have grown and I would have certainly lost the kidney." Go to post
Want to connect with other people living with kidney cancer and their caregivers today? Visit the Inspire Kidney Cancer Community.
Sources
https://www.niddk.nih.gov/health-information/kidney-disease/simple-kidney-cysts
https://www.sciencedirect.com/science/article/abs/pii/S1571467509000649
https://cancerimagingjournal.biomedcentral.com/articles/10.1186/s40644-021-00419-1
Disclaimer
Member comments have been lightly edited for length and clarity. This content is for general informational purposes only and does not necessarily reflect the views and opinions of any organization or individual. The content should not be used as a substitute for professional medical advice, diagnosis, or treatment. Please consult your healthcare provider about any questions you may have regarding a medical condition.
