Are small renal masses all the same?

To evaluate variables that can predict synchronous metastasis in patients presenting with small renal masses.

We reviewed our institution's prospectively maintained database of 565 patients diagnosed with small renal masses (≤4 cm) over a 16-year period. Variables associated with synchronous metastasis and subsequent relapse were analyzed using χ² and logistic regression models.

A total of 16 patients (2.7%) presented with synchronous metastasis. Just three patients with tumor size <3 cm had metastatic disease at presentation. On multivariate analyses, tumor size >3 cm, symptomatic cancer, age >65 years and ipsilateral synchronous tumors were independent predictors of M1 renal cell carcinoma. A weighted predictive model (concordance index 0.786) showed that a score ≥2 significantly increases the risk of synchronous metastasis (7.9% vs <1% for score <2, P < 0.01, hazard ratio 12.56, 95% confidence interval 5.52-22.85). A total of 498 (90.7%) patients underwent nephrectomies, 27 (4.9%) had ablative therapies and 24 (4.4%) continued on active surveillance/watchful waiting. Over a median follow-up period of 62.8 months, 30 patients (6.1%) had disease recurrence. On multivariate analyses, higher Fuhrman grade and lymphovascular invasion were independent predictors of recurrence. A separate predictive model (concordance index 0.723) showed that either pathological outcome increases recurrence risk up to 15% (P < 0.01, hazard ratio 11.83, 95% confidence interval 5.82-18.76).

Several clinical variables can better identify the metastatic potential of small renal masses. The two proposed predictive models can be valuable tools in future clinical practice.