Small renal cell carcinomas--how dangerous are they really? Results of a large multicenter study.

Aim Of The Study: Modern diagnostic ultrasound and cross-sectional imaging has enabled the detection of increasing numbers of renal tumours. The aim of this study was to investigate the tumour- and patient-specific characteristics and prognosis of small renal cell carcinomas (RCCs) after surgical resection.

Methods: The study included 2197 patients who underwent surgical resection of histologically confirmed RCC ⩽ 4 cm between 1990 and 2011. Median (mean) follow-up was 56.2 (65.5) months.

Results: At the time of surgery, tumours were staged as pT ⩾ 3a in 175 (8.0%) cases, 134 (6.2%) were poorly differentiated and 75 (3.5%) were metastasised. The larger the tumour size, the higher was the risk of presenting with stage pT ⩾ 3a (p<0.001), poor tumour differentiation (p = 0.004), microscopic vascular involvement (p = 0.001) and collecting system invasion (p = 0.03). The 5-year cancer-specific survival (CSS) rate was 93.8% for stage pT1a versus 79.4% for stage pT ⩾ 3a (p<0.001), and it was 93.7% for G1-2 versus 76.8% for G3-4 differentiation (p<0.001). Multivariate analysis identified age in years (hazard ratio (HR) 1.04, p<0.001), metastatic disease (HR 12.5, p < 0.001), tumour differentiation (HR 2.8, p<0.001) and non-clear cell histology (HR 0.51, p = 0.02) as independent prognosticators for CSS in patients with small RCC. Interestingly, the 5-year cancer-specific mortality rate for pT1a N/M0 patients was 5.8%.

Conclusions: This large multicenter study has clearly shown that, though most small RCC have a low pathological stage and a good prognosis, there is also a small but significant subgroup of these tumours that are already locally advanced or poorly differentiated.