Presentation Authors: Mary E Westerman*, Vidit Sharma, Christine Lohse, Stephen A. Boorjian, Bradley C. Leibovich, John C. Cheville, R. Houston Thompson, Rochester, MN
Introduction: In 2016, the World Health Organization reorganized low grade cystic renal epithelial neoplasms, previously broadly termed cystic clear cell renal cell carcinoma (RCC), into three tumor subtypes - multilocular cystic neoplasm of low malignant potential (MCNLMP), cystic clear cell RCC, and cystic clear cell papillary RCC. We report on the incidence and long term oncologic outcomes of these subtypes of low grade cystic renal epithelial neoplasms.
Methods: We identified 3,865 patients treated with radical or partial nephrectomy for unilateral, sporadic clear cell RCC between 1970 and 2010, of whom 145 (4%) had low grade cystic renal epithelial neoplasms based on 2004 WHO criteria. One urologic pathologist re-reviewed all pathologic slides, blinded to patient outcome. Oncologic outcomes were estimated using the Kaplan-Meier method.
Results: Of 145 specimens 18 (12%) were classified as MCNLMP, 95 (66%) cystic clear cell RCC and 32 (22%) cystic clear cell papillary RCC. Those with MCNLMP were more likely female (61% versus 29% versus 31%, p=0.03) with larger tumors (median 4.6 cm versus 3.0 versus 2.3, p=0.02) compared to those with cystic clear cell RCC and cystic clear cell papillary RCC, respectively. Only 2% of cystic clear cell RCC had tumor necrosis or grade 3 nucleoli present. With a median follow-up for survivors of 10.3 years (IQR 7.4-14.9), 60 patients died at a median of 7.6 years following surgery (IQR 3.7-11.8). One patient with cystic clear cell RCC died after experiencing distant metastases to the lungs, bone, and brain 22 years after surgery. Ten and 20 year cancer-specific survival was 100% across all subtypes (Table 1).
Conclusions: In a large cohort of patients previously classified as cystic RCC with pathologic re-review and long-term follow-up, MCNLMP is the least common subtype of low grade cystic renal epithelial neoplasms. However, when treated surgically, all subtypes are associated with an excellent long term prognosis.