Renal Mass (Kidney Tumor)

A renal mass is an abnormal growth in or on the kidney. Kidney cancer is among the ten most common cancers in the United States, with approximately 80,000 new cases diagnosed each year. The average age at diagnosis is 65, and the condition is more common in men than women. However, not every kidney mass is cancer — approximately one in four renal masses turns out to be benign, and smaller masses are even more likely to be noncancerous.

How Renal Masses Are Found

Over half of kidney masses today are discovered incidentally — found on a CT scan, ultrasound, or MRI ordered for an entirely unrelated reason such as abdominal pain, a trauma workup, or routine health screening. Less than 5% of patients present with the classic triad of symptoms (blood in the urine, flank pain, and a palpable mass). Because of the widespread use of cross-sectional imaging, at least 40% of newly detected kidney tumors are small, localized masses caught at an early stage when treatment is most effective and outcomes are best.

Benign Kidney Tumors

The two most common benign kidney tumors are:

• Angiomyolipoma (AML) — A tumor made up of blood vessels, smooth muscle, and fat tissue. AMLs are more common in women and can often be identified on imaging by their fat content. Most small AMLs can be safely monitored without surgery. Larger AMLs (typically over 4 cm) or those causing symptoms may need treatment due to a risk of bleeding.
• Oncocytoma — A benign tumor that accounts for 3% to 7% of all kidney tumors, seen more often in men. Oncocytomas are almost always cured by surgical removal and it is extremely rare for them to spread. Unfortunately, they can look very similar to kidney cancer on imaging, which is why biopsy or surgical removal may be recommended when oncocytoma is suspected.

Malignant Kidney Tumors (Kidney Cancer)

About 9 out of 10 kidney cancers are renal cell carcinoma (RCC). The major subtypes include:

• Clear cell RCC — The most common subtype, accounting for about 70% of kidney cancers. Tends to respond well to treatment when caught early.
• Papillary RCC — The second most common subtype, making up about 10% of cases.
• Chromophobe RCC — Accounts for roughly 5% of kidney cancers and generally carries a favorable prognosis.

The overall five-year survival rate for kidney cancer across all stages is approximately 76%, and for cancers caught at an early, localized stage the outlook is significantly better. Kidney cancer mortality has been steadily declining at a rate of about 1% per year since 2004.

Evaluation: Imaging and Biopsy

A CT scan with intravenous contrast is the cornerstone of renal mass evaluation. It reveals tumor size, location, and internal characteristics — and whether the mass enhances (takes up contrast), which is a key indicator of a solid, potentially cancerous growth. For patients who cannot receive CT contrast, MRI with gadolinium provides comparable detail. Dr. Radtke uses standardized complexity scoring systems (such as the R.E.N.A.L. Nephrometry Score) to objectively assess each tumor and guide treatment planning.

In select cases, a needle biopsy may be recommended — particularly when imaging findings are unclear, when active surveillance is being considered, or before thermal ablation. Modern renal mass biopsy is safe and accurate, with diagnostic rates exceeding 90% in experienced hands.

Treatment Options

Treatment depends on tumor size, location, and characteristics, as well as your kidney function and overall health. Options include:

• Active surveillance — For small renal masses (typically under 2 cm) or patients where treatment risks outweigh benefits. Research shows that monitored tumors grow an average of only 0.28 cm per year, and progression to metastasis occurs in only about 1% of surveilled patients.
• Robotic partial nephrectomy — The preferred surgical approach for most kidney tumors. Removes only the tumor and a thin margin of normal tissue, preserving the rest of the kidney to protect long-term kidney function.
• Robotic radical nephrectomy — Removal of the entire kidney, reserved for larger tumors, tumors in challenging locations, or confirmed cancers that cannot safely be removed with a partial approach.
• Thermal ablation — Cryoablation (freezing) or radiofrequency ablation (heating) can destroy small tumors (generally under 3 cm) without removing them. Best suited for patients who may not be ideal surgical candidates. A biopsy is recommended before ablation to confirm the diagnosis.