SIU 2017: Rationalising Follow Up for Bosniak IIF Cysts: A Multicentre Study

Lisbon, Portugal ( In this study, the authors build upon work they had previously published in 2016. In that study, they demonstrated that in a cohort of 198 patients with Bosniak IIF cysts, only 0.5% progressed into malignant lesions; if they progressed, it was within the first two years of follow-up. They had then recommended that patients with Bosniak IIF cysts could be discharged from follow-up after 2 stable years. In this study, they replicate similar findings in a separate institution.

In this abstract, they identified patients with Bosniak IIF cysts on CT imaging over a 4-year period at two separate NHS systems. Progression was defined as any change in size, appearance or complexity. Patient demographics, radiographic follow-up and need for intervention were recorded. 

A total of 249 patients were identified with Bosniak IIF cysts over this time frame. The majority were incidental findings (>80%) and approximately 50% were > 3 cm at the time of diagnosis. Median follow-up for the cohort was 29 months (2.5 years). The confirmed malignancy rate was 0.8%. 76.5% of patients had stable, unchanged cysts over the follow-up period; 2.8% had radiographic progression so they underwent radical intervention – of those, only 2 (0.8%) had malignancy. 

Based on this, the authors state the confirmed malignancy rate is 0.5-0.8% for Bosniak IIF cysts, which is much lower than prior series. They continue to push for cessation of follow-up after 2 years. 

While we inherently agree with the principle, specifically the low malignant potential of Bosniak IIF cysts, there are significant flaws in their logic. It is impossible to state that the confirmed malignancy rate is only 0.5-0.8% - of the 2.8% that were treated, 2 patients had malignancy. However, they cannot be certain there isn’t malignancy in the remaining 97% of patients. Hence the calculated malignancy rate should be 0.8/2.8, which is almost 30%. It is likely smaller than this, which would be consistent with historical series. Also, with median follow-up of 2.5 years, it is hard to definitely state that there will not be later progression. 

Despite all that, data from a recent systematic review by Schoots et al supports the idea that Bosniak IIF have low malignant potential. More importantly, both have very low potential for metastatic spread. Active surveillance can be a legitimate treatment option for both lesions.

1 Schoots IG, et al. Bosniak Classification for Complex Renal Cysts Reevaluated: A Systematic Review. J Urol. 2017 Jul;198(1):12-21. doi: 10.1016/j.juro.2016.09.160. Epub 2017 Mar 9.

Presented by: Sotonye Tolofari 

Written by: Written by: Thenappan Chandrasekar, MD, Clinical Fellow, University of Toronto, twitter: @tchandra_uromd, at the 37th Congress of Société Internationale d’Urologie - October 19-22, 2017- Lisbon, Portugal