Presentation Authors: Ahmed Aly Hussein Aly, Shervin Badkhshan*, Arun Menon, David Abramowitz, Michael Vacchio, Daniel Wang, Amanda Sherman, Kevin Carocci, Michael Petroziello, Charles Roche, Bo Xu, Eric Kauffman, Buffalo, NY
Introduction: Occasional spontaneous shrinkage of renal tumors under active surveillance (AS) is a well-documented phenomenon, but the histology of these shrinking tumors is unknown due to lack of widespread biopsy during AS. Here we describe the incidence and features of histologically confirmed renal cell carcinoma (RCC) with spontaneous shrinkage during AS, including novel discovery of common spontaneous regression among non-clear cell subtypes.
Methods: A prospectively maintained kidney tumor AS database at a single National Comprehensive Cancer Network institute was queried to identify all AS patients with clear cell RCC (ccRCC), chromophobe RCC (chRCC) or papillary RCC (pRCC) diagnosed by percutaneous biopsy with >/=6 months follow-up. Shrinking tumors (>30% volume reduction) were confirmed by radiologist re-review. Needle core biopsies of all shrinking tumors and a subset of growing tumors were scored by a genitourinary pathologist for various histologic features including macrophage and lymphocytic infiltration, eosinophilia and necrosis.
Results: 74 AS patients with RCC on biopsy were identified (42 ccRCC, 24 pRCC 8 chRCC). Intriguingly, 9/24 (38%) pRCC and 4/8 (50%) chRCC shrunk during AS without treatment, compared to only 1/42 (2%, p=0.03 and 0.03, respectively) ccRCC. The median tumor volume shrinkage (range) was 57% (31-84%) for pRCC, 83% (68-97%) for chRCC, and 31% for ccRCC. Shrinkage temporally followed the tumor biopsy in all but 2 cases. Most shrinking pRCC tumors demonstrated extensive macrophage infiltration compared to only moderate, low or absent levels in all growing pRCC tumors (Figure 1). Shrinking chRCC tumors exhibited diffusely intense eosinophilia in 3 of 4 cases, whereas shrinking ccRCC tumor lacked substantial eosinophilia or macrophage infiltration .
Conclusions: In among the largest series of biopsied RCC tumors on AS to our knowledge, we discovered a novel phenomenon of common spontaneous tumor regression among non-clear cell subtypes. Macrophage infiltration and temporal association of tumor regression with biopsy suggest a possible immune etiology. Spontaneous RCC shrinkage has implications for AS patient selection and warrants additional study to identify clinical, histologic and molecular predictors.