AB88. Natural history of renal cell carcinoma: an immunohistochemical analysis of growth rate in patients with delayed treatment

BACKGROUND/PURPOSE To investigate the natural history of renal cell carcinoma (RCC) with delayed treatment and to immunohistochemically analyze the correlation between some biomarkers and the growth rate of RCC. METHODS We reviewed our institutional databases to identify renal tumors which were confirmed to be RCC by delayed surgical treatment after at least 12 months of active surveillance (AS). Growth rate was defined as the average growth rate of the maximal diameter on computed tomography or magnetic resonance imaging. The clinicopathological characteristics and immunohistochemical biomarkers (Ki-67, p53, bcl-2, and vascular endothelial growth factor) were analyzed the correlation with the growth rate of RCC. RESULTS We identified 45 RCCs from 45 patients. The mean patient age was 54 years (range, 26-78 years). The mean tumor size increased from 2.39 cm (range, 0.10-6.70 cm) at presentation to 4.54 cm (range, 1.40-11.80 cm) after a mean time of 45.4 months (range, 12-155 months) of AS. The mean growth rate was 0.79 cm/y (range, 0.10-4.74 cm), and 36 (80.0%) tumors presented a growth rate ≤ 1.00 cm/y. Clear cell RCC had a trend of growing faster than other histological subtypes. Pathological grade was significantly correlated with the growth rate of RCC (p = 0.043). High positive ratio of Ki-67 (r = 0.351, p = 0.018) and being p53 positive (p = 0.019) were significantly correlated to the fast growth rate of RCC. CONCLUSION In general, RCCs under AS are slow growing with a wide variation of growth rate, with a portion of RCCs presenting rapid growth kinetics. RCC with rapid growth during AS is characterized by a high histological grade, high positive ratio of Ki-67, and being p53 positive.