Benign renal neoplasms are non-cancerous growths in the kidneys that typically don’t pose a threat to life, but understanding them is important for making the right health decisions.

Treatment approaches: What matters most for benign kidney growths

When you discover that you have a benign kidney tumor, the first thing to understand is that treatment choices depend heavily on individual circumstances. The main goal of managing these growths is not about curing cancer—because these tumors are not cancerous—but rather about preventing potential complications and preserving your kidney function and overall quality of life.^[1]

A benign tumor (also called non-cancerous or benign neoplasm) is a mass of cells that grows in an abnormal way but does not spread to other parts of your body. In the kidney, these growths are actually quite common. In fact, up to 20 to 30 percent of small kidney masses turn out to be benign when examined more closely.^[3][10]

The decision about whether to treat a benign kidney tumor—and how to treat it—depends on several factors. These include the size of the tumor, whether it’s causing any symptoms, its exact location in the kidney, and your overall health status. Many small benign kidney tumors don’t cause any problems at all and may be discovered accidentally during imaging tests ordered for completely unrelated reasons.^[1][4]

The management approach also takes into account whether the tumor might grow over time, whether it could damage surrounding kidney tissue, and whether it might cause bleeding or other complications. Because you have two kidneys, doctors also consider how much kidney function you have and whether any treatment might affect that function.^[9]

Standard treatment: What doctors typically recommend

Surgery remains the primary treatment method for most benign kidney tumors that require intervention. The reason is straightforward: even though these growths are not cancerous, they can sometimes grow large enough to cause problems, and removing them is often the most effective way to prevent complications.^[1][8]

There are different surgical approaches depending on the size and location of the tumor. In many cases, surgeons can perform a partial nephrectomy, which means removing only the tumor and a small margin of healthy tissue around it while leaving the rest of the kidney intact. This approach is preferred whenever possible because it preserves kidney function.^[9]

For larger tumors or those in difficult locations, a complete nephrectomy (removal of the entire kidney) might be necessary. However, this is generally avoided unless absolutely required, especially if your other kidney has any functional problems.^[1]

Not all benign kidney tumors need immediate surgery. For small tumors that aren’t causing symptoms, doctors often recommend active surveillance. This means regular monitoring with imaging tests—typically every three to six months initially, then less frequently if the tumor remains stable. Active surveillance is especially appropriate for small masses less than 3 centimeters (about 1.2 inches), tumors that are growing very slowly, and patients who have other health conditions that might make surgery risky.^[4][12]

For specific types of benign kidney tumors, there are specialized treatment options. Angiomyolipomas, which are tumors made up of fat, blood vessels, and smooth muscle tissue, can sometimes be managed with arterial embolization. This procedure involves blocking the blood vessels that feed the tumor, causing it to shrink. This approach is particularly useful when the tumor is large or when bleeding is a concern, but surgery would be too risky.^[1][2]

The duration of treatment varies. Surgery is typically a one-time procedure, though recovery can take several weeks. You’ll usually stay in the hospital for a few days after a partial nephrectomy, and full recovery may take four to six weeks. During this time, it’s important to avoid strenuous activities and follow your doctor’s instructions about wound care and pain management.^[9]

Side effects of surgery can include pain at the incision site, temporary changes in kidney function, bleeding, infection, or damage to nearby organs. Most patients recover well, especially when only part of the kidney is removed. Long-term complications are relatively rare, but may include reduced kidney function if a large portion of kidney tissue was removed.^[9]

Types of benign kidney tumors and their characteristics

Papillary renal adenoma is the most common type of benign kidney tumor. These growths are typically small and grow very slowly. Most people with papillary renal adenomas have no symptoms at all, and these tumors are usually found by accident during imaging tests done for other reasons. Because they rarely cause problems, they often don’t require treatment beyond monitoring.^[1][6]

Oncocytomas start in the cells of the collecting ducts, which are part of the kidney’s filtering system. These tumors can grow quite large—sometimes reaching several inches in diameter. One unusual feature of oncocytomas is that multiple tumors can develop in one or both kidneys. They grow slowly and typically don’t spread. However, because they can appear very similar to cancerous tumors on imaging tests, a biopsy or surgery is sometimes needed to confirm the diagnosis.^[1][4]

Angiomyolipomas are kidney tumors composed of three types of tissue: fat, blood vessels, and smooth muscle. These tumors often develop in people with a genetic condition called tuberous sclerosis, which causes benign tumors to form in multiple organs throughout the body. However, angiomyolipomas can also occur in people without this condition.^[1][2]

Even though angiomyolipomas are not cancerous, they can cause serious complications. They can invade and destroy surrounding kidney tissue. More importantly, larger angiomyolipomas—especially those bigger than 4 centimeters (about 1.6 inches)—carry a risk of sudden bleeding into the abdomen, which is a medical emergency. This is because the blood vessels in these tumors are often abnormal and fragile.^[1][2]

Angiomyolipomas appear golden yellow because of their fat content, and their size can range from about half an inch to 8 inches (1 to 20 centimeters). The growth rate varies, but on average, they grow slowly—about one-sixteenth of an inch (0.19 centimeters) per year. However, they may grow more rapidly during pregnancy, which is why women with known angiomyolipomas may need treatment before becoming pregnant.^[2]

Simple kidney cysts: A common benign condition

Simple kidney cysts are the most common non-cancerous condition affecting the kidneys. These are round or oval fluid-filled sacs that can develop in one or both kidneys. They’re extremely common in people over 50 years old. In fact, many older adults have at least one kidney cyst without knowing it.^[1][8]

Most simple kidney cysts are found accidentally during imaging tests done for other medical reasons. On imaging tests like CT scans or ultrasounds, simple cysts have very distinctive features: they have smooth, well-defined edges and are perfectly round. These characteristics help doctors distinguish them from kidney tumors.^[1]

The good news is that simple kidney cysts usually don’t need any treatment. They don’t cause symptoms and don’t interfere with kidney function. However, if a cyst starts causing problems—such as pain, infection, or bleeding—doctors can drain it using a long needle or remove it surgically.^[1][8]

When symptoms occur: What to watch for

Many people with benign kidney tumors never experience any symptoms. This is especially true for small tumors. However, as a tumor grows larger, symptoms may begin to appear.^[6][7]

Blood in the urine, called hematuria, is one of the most important warning signs. Sometimes the blood is visible to the naked eye, making the urine appear pink, red, or cola-colored. Other times, the blood can only be detected under a microscope during a urinalysis. If you notice blood in your urine, it’s important to see a healthcare provider right away, even though it might be caused by something less serious like a urinary tract infection.^[6][7]

Pain is another possible symptom. This may be felt in the lower back, in the area between the ribs and hips (called the flank), or as a persistent ache on one side. The pain might be constant or come and go.^[6][7]

Some people experience loss of appetite and unexplained weight loss. You might find that you have no interest in food, or that you feel full very quickly after starting to eat. These symptoms can affect your overall energy levels and well-being.^[6]

Anemia (low red blood cell count) can develop if a kidney tumor affects the kidney’s ability to produce a hormone called erythropoietin (EPO), which helps the body make red blood cells. Anemia can also occur if you’re losing red blood cells through bleeding in your urine. Signs of anemia include fatigue, weakness, pale skin, and shortness of breath.^[6]

Fever is another possible symptom. This might be a low-grade fever that comes and goes, or it might be continuous. The fever may be linked to an infection or to the tumor itself.^[6][7]

For angiomyolipomas specifically, larger tumors can cause sudden, severe bleeding into the abdomen. This is a medical emergency that requires immediate attention. Symptoms might include sudden, severe abdominal pain, dizziness, rapid heartbeat, or signs of shock.^[2]

Diagnosis: How benign kidney tumors are detected

Most benign kidney tumors are found incidentally—meaning they’re discovered by chance during imaging tests ordered for completely different reasons. For example, you might have a CT scan for abdominal pain or back pain, and a kidney tumor shows up unexpectedly.^[4][12]

Once a kidney mass is detected, several tests help doctors understand what they’re dealing with. Imaging tests are the cornerstone of diagnosis. An ultrasound can show whether a mass is solid or filled with fluid (cystic). CT scans (computed tomography) are considered the gold standard for evaluating kidney masses because they provide detailed, three-dimensional images that show the size, location, and characteristics of the tumor. MRI (magnetic resonance imaging) scans are useful when CT scans can’t be used, such as in patients with allergies to contrast dye or poor kidney function.^[4][7]

For cystic (fluid-filled) kidney masses, doctors use something called the Bosniak Classification System to assess the risk that a cyst might be cancerous. Bosniak I and II cysts are simple and usually benign, requiring no follow-up. Bosniak IIF cysts are slightly more complex and need follow-up imaging every 6 to 12 months. Bosniak III cysts have irregular features and surgery is usually recommended. Bosniak IV cysts show signs of cancer and definitely require surgical removal.^[4]

Blood tests and urine tests help evaluate kidney function and look for signs of bleeding or infection. A urinalysis checks for blood cells and other substances in your urine. Blood tests measure how well your kidneys are filtering waste and can also check for anemia.^[7]

In some cases, a biopsy may be recommended. This involves removing a small sample of tissue from the tumor using a thin needle, which is then examined under a microscope. Biopsies are particularly useful when there’s concern about a rare tumor type, when surgery would be very risky for the patient, or when the person already has cancer elsewhere in the body.^[4]

One challenge in diagnosing benign kidney tumors is that they can look very similar to cancerous tumors on imaging tests. Angiomyolipomas are somewhat easier to identify because the presence of fat tissue shows up clearly on CT scans. However, oncocytomas are notoriously difficult to distinguish from kidney cancer, even with advanced imaging, which is why a biopsy or surgery is sometimes the only way to know for certain.^[4]

Treatment in clinical trials: Exploring new approaches

While benign kidney tumors themselves are not the focus of most clinical trials, research into kidney masses in general has led to important advances in how we manage these conditions. Much of the ongoing research focuses on better ways to distinguish benign tumors from cancerous ones without surgery, and on minimally invasive treatment options.

Research has strongly supported the use of active surveillance for small kidney masses, including those that might be benign. Large studies, such as the Delayed Intervention and Surveillance for Small Renal Masses (DISSRM) Registry, have shown that patients under active surveillance have excellent outcomes. This registry reported a 100 percent cancer-specific survival rate over 5 years for patients who chose monitoring over immediate treatment.^[21]

Other research has focused on the rates of serious complications in patients who are monitored rather than treated immediately. A large review published in the medical journal Cancer found that only 1 to 2 percent of patients under active surveillance for 2 to 3 years developed metastatic disease. These findings support the safety of careful observation for selected patients with small kidney masses.^[21]

Clinical guidelines from the American Urological Association have been updated based on this research. The guidelines now endorse an initial period of active surveillance instead of immediate treatment as an option for small lesions measuring less than 2 centimeters. This represents a significant shift in thinking about how to manage small kidney masses.^[21]

Researchers are also working on developing new tests that could more accurately identify which tumors are safe to observe and which require intervention. These include advanced imaging techniques and molecular tests that analyze tissue samples in new ways. The goal is to avoid unnecessary surgery for benign tumors while ensuring that cancerous growths are treated promptly.^[21]

For angiomyolipomas specifically, studies are looking at the best timing and technique for arterial embolization. This treatment, which blocks the blood vessels feeding the tumor, can be an alternative to surgery in certain situations. Research is examining which patients benefit most from this approach and how to minimize complications.^[1]

Most common treatment methods

• Active surveillance
  • Regular monitoring with imaging tests every 3 to 6 months for small, slow-growing tumors that don’t cause symptoms
  • Particularly appropriate for tumors less than 3 centimeters in size
  • Studies show excellent outcomes with 100 percent cancer-specific survival over 5 years in monitored patients
  • Allows treatment to be reconsidered if the tumor begins to grow or causes problems
• Surgical removal
  • Partial nephrectomy removes only the tumor and preserves most of the kidney
  • Complete nephrectomy removes the entire kidney when necessary
  • Tumors typically don’t come back after surgical removal
  • Recovery takes several weeks with hospital stay of a few days
• Arterial embolization
  • Blocks blood vessels feeding the tumor, causing it to shrink
  • Particularly useful for angiomyolipomas
  • Alternative when surgery is too risky or for tumors at risk of bleeding
• Cyst drainage or removal
  • For simple kidney cysts that cause pain, infection, or bleeding
  • Can be drained using a long needle or removed surgically
  • Most simple cysts don’t require any treatment