What is the management approach for a Bosniak (Bosniak classification system) 2F cystic left renal mass, given that the majority are benign and malignant cases are typically indolent?

From the Guidelines

I strongly recommend regular imaging follow-up for the Bosniak 2F cystic left renal mass with CT or MRI at 6 months, 12 months, and then annually for a total of 5 years to monitor for stability, as this approach is supported by the most recent and highest quality evidence, including the European Association of Urology guidelines on renal cell carcinoma 1. Bosniak 2F renal cysts have some concerning features but are predominantly benign, with studies showing that approximately 90% of these lesions are non-malignant 1. In the minority of cases where malignancy is present, these tumors typically demonstrate indolent behavior with slow growth and low metastatic potential.

The recommended surveillance protocol allows for early detection of any changes that might indicate malignant transformation while avoiding unnecessary invasive procedures for what is likely a benign condition. If during follow-up the mass shows concerning changes such as increasing complexity, developing solid components, or significant growth, then reevaluation and possible intervention would be warranted. This approach balances the low risk of malignancy against the potential complications of more aggressive management, prioritizing the patient's quality of life and minimizing the risk of morbidity and mortality 1.

Key points to consider in the management of Bosniak 2F cystic left renal mass include:

• The Bosniak classification system is used to predict the risk of malignancy and guide management 1
• Bosniak 2F cysts have a low risk of malignancy, with approximately 10% of lesions progressing to malignancy 1
• Regular imaging follow-up is necessary to monitor for stability and detect any changes that may indicate malignant transformation 1
• The surveillance protocol should be individualized based on the patient's overall health, preferences, and values 1

By following this approach, clinicians can provide optimal care for patients with Bosniak 2F cystic left renal mass, minimizing the risk of morbidity and mortality while prioritizing quality of life 1.

From the Research

Bosniak 2F Cystic Renal Masses

• Majority of Bosniak 2F masses are benign, as indicated by studies such as 2 and 3
• When malignant, nearly all are indolent, suggesting a slow progression of the disease 2
• Generally, Bosniak 2F masses are followed at imaging (CT or MRI) at 6 months and 12 months and then annually for a total of 5 years to assess for stability 2

Imaging Surveillance

• The currently recommended initial 6-month follow-up imaging examination for class IIF masses is of questionable clinical utility, as only 4% were upgraded over time and never on initial 6-month follow-up 2
• CT and MRI were concordant in the majority of cases using Bosniak classification version 2019, and category changes by modality were not statistically significant 4
• MRI has specific advantages and is recommended to evaluate masses that at computed tomography (CT) have abundant thick or nodular calcifications, are homogeneous, hyperattenuating, ≥3 cm, and nonenhancing, or are heterogeneous and nonenhancing 5

Malignancy Rates

• Pooled proportions of malignancy by class were as follows: II, 9% (95% CI: 5-17%); IIF, 26% (95% CI: 13-46%); III, 80% (95% CI: 71-87%); and IV, 88% (95% CI: 83-91%) 3
• The proportion of malignancy was 41% for IIF masses with histopathology reference versus 2% for IIF masses with imaging follow-up reference, indicating verification bias 3

Management

• Small size should be a consideration for conservative management, as approximately one-half of small (< 4 cm) Bosniak category 3 and 4 cystic renal lesions were downgraded, and the majority (88%) of small Bosniak category 2F lesions regressed or remained stable during active surveillance 6