Renal cell carcinoma (RCC) is the most prevalent form of kidney cancer in adults. A rare subtype is cystic renal cell carcinoma (cRCC), defined by the presence of one or more fluid-filled sacs, or cysts. This subtype presents differently than solid kidney tumors in both its structure and behavior.
Defining Cystic Renal Cell Carcinoma
Cystic renal cell carcinoma tumors are composed of fluid-filled components, giving them a different architecture than the dense masses of most kidney cancers. It is important to distinguish these from simple renal cysts, which are common, almost always benign, and do not require intervention.
To differentiate these cysts, radiologists use the Bosniak classification system. This system evaluates kidney cysts on imaging scans, such as a CT scan, and categorizes them on a scale from I to IV based on their likelihood of being cancerous. A simple, thin-walled cyst with no complex features is a category I.
As cysts show more concerning features like thickened walls, multiple partitions (septa), or solid areas that enhance with contrast dye, their Bosniak category increases. Category III lesions are considered indeterminate, with over 50% being malignant. Category IV lesions contain enhancing soft-tissue components and are considered cancerous, requiring intervention or close monitoring.
Symptoms and Diagnosis
Many cystic renal cell carcinomas are asymptomatic and discovered incidentally during an imaging test for an unrelated issue. When symptoms do occur, they can include pain in the side or lower back, blood in the urine (hematuria), or a noticeable lump in the abdomen.
The diagnostic process relies on advanced imaging like contrast-enhanced CT scans and MRIs. These scans provide detailed pictures of the cyst’s walls, septa, and any solid components. This detail allows radiologists to categorize the mass using the Bosniak scale to assess its potential for malignancy.
If imaging is not definitive, a needle biopsy to extract a tissue sample may be considered. However, biopsies of cystic masses can yield inconclusive results. Because of this, doctors may proceed with treatment based on imaging features alone, particularly for cysts in higher Bosniak categories.
Common Treatment Approaches
For small, low-risk cystic lesions, active surveillance is a common course of action. This approach involves monitoring the mass with regular imaging scans to see if it grows or changes over time. Active surveillance is often recommended for older patients or those with other significant health issues.
When treatment is necessary, surgery is the primary approach. The preferred method is a partial nephrectomy, where the surgeon removes the tumor while preserving healthy kidney tissue. This nephron-sparing surgery helps maintain overall kidney function.
In cases where the tumor is large or centrally located, a radical nephrectomy—the removal of the entire kidney—might be performed. Less invasive techniques like thermal ablation are also available. Ablation uses extreme cold (cryoablation) or heat (radiofrequency ablation) to destroy tumor tissue and is an alternative for patients who are not good candidates for surgery.
Prognosis and Post-Treatment Monitoring
The prognosis for cystic renal cell carcinoma is generally favorable compared to solid kidney cancers. These tumors are less aggressive and have a lower tendency to metastasize, or spread to other parts of the body. When detected early and treated with surgery, the rates of recurrence are low.
After treatment, the recovery process depends on the procedure performed. A partial nephrectomy or an ablative procedure usually involves a shorter hospital stay and quicker return to normal activities than a radical nephrectomy.
Long-term management involves regular follow-up appointments and imaging scans to monitor for cancer recurrence. A typical follow-up schedule might involve imaging every six months for the first few years, followed by annual scans.