The growth rate of large renal masses opposes active surveillance.

Objective: To retrospectively determine the growth rate of renal masses with a diameter of > or =4 cm at the time of surgery, as the average growth rate of untreated small (<4 cm) renal masses is assumed to be 0.1-0.7 cm/year, but little is known about the progression of large masses.

Patients And Methods: Of 256 patients who had their renal tumour surgically removed between January and December 2008, we identified nine (five men and four women; median age 65.2 years, range 29.2-74.2) with solitary large renal masses (>4 cm) who had abdominal imaging with identification of renal masses >6 months before admission. In none of the patients had the initial imaging led to admission, either by accident or because the masses were overlooked. The tumour growth rate was calculated based on images taken > or =6 months before admission and actual imaging, as well as histological results.

Results: All patients had surgical resection of their renal masses in 2008. The median (range) follow-up from initial diagnosis to surgery was 14.6 (6.5-58.4) months. The median observed tumour growth rate was 6.41 (2.47-8.66) cm/year. The histological diagnosis was clear cell renal cell carcinoma (RCC) in seven patients, papillary in one and clear cell RCC with portions of sarcomatoid de-differentiation in one; two patients had lymph node metastases and one had pulmonary metastases, and five had tumours of > or =T3.

Conclusions: The growth rate of large tumours is much higher than of small renal masses and most patients present with advanced disease. Thus, tumours of > or =4 cm seem not to be candidates for active surveillance but require immediate therapy. Further studies are warranted to determine the clinical relevance of progressive tumour growth and the underlying mechanisms.