The natural history of small renal masses.

Purpose: Ultrasound, computerized tomography and magnetic resonance imaging are widely available. Incidentally discovered small renal masses are reported more frequently. Most of these masses are low stage renal cell carcinomas. To understand better the natural history of these lesions and offer appropriate management, we followed prospectively a series of patients with this type of lesion.

Materials And Methods: A total of 13 patients with radiologically detected solitary small renal masses who were unfit for or refused surgery were followed with abdominal imaging for a median of 42 months. Median patient age was 69 years and mean lesion volume at diagnosis was 13.6 cm.3 or 2.95 cm. in diameter. Growth rate was calculated based on tumor volume rather than bi-dimensional diameter. Individual slopes of tumor size in time were calculated.

Results: Of the 13 patients 5 underwent surgery following a period of surveillance because of apparent tumor enlargement or new onset of symptoms. Pathological evaluation revealed renal cell carcinoma in all 5. No patient had metastases. Only 2 tumors were fast growing and these were the only 2 cases in which symptoms developed. When these patients were excluded from analysis, average growth rate was 1.32 cm.3 per year (p = 0.5, 95% confidence interval -3.00 to 5.76 cm.3 per year), which was not statistically significantly different from 0 slope or no growth.

Conclusions: These results demonstrate that the growth rate of small renal tumors is variable, tumors that are destined to grow and possibly metastasize do so early and most small tumors grow at a low rate or not at all.