Does Size Predict Aggressiveness?: Exploring Sporadic Multifocal Tumors in a 10-Year Retrospective Analysis

For localized kidney tumors, size and growth kinetics generally predict malignant potential. Thus, for patients with multifocal renal masses, treatment priority often revolves around the largest or index tumor first. We reviewed our kidney surgery database to examine histologic concordance of sporadic multifocal renal tumors and to determine if size is also the greatest determinant of tumor aggressiveness.

We conducted a retrospective chart review at a tertiary referral center of 1983 patients undergoing nephrectomy (radical and partial) from January 2010 to December 2019. We identified 138 patients with multifocal renal masses (n = 138). Surgical pathology parameters, including tumor size, TNM grading, and staging, were collected through electronic medical records. Patients with syndromic diseases were excluded (n = 10), resulting in a total sample of 128 patients with sporadic multifocal tumors. Overall, the sample included 307 tumors total, with a mean number of 2.4 lesions per patient.

About 128 patients (6.45%) had sporadic multifocal renal tumors. Among these, 82 out of 128 (64%) had concordant histologic subtypes, while 46 out of 128 (36%) had discordant histology. In 99 patients (77.3%), the index tumor demonstrated a more aggressive histology. There were 29 patients (22.6%) with a benign or less aggressive index tumor. Among those, 21 patients (16%) had a benign index tumor, 5 (24%) of which had a malignant secondary tumor.

Multifocal tumors frequently have discordant histology. While size tends to predict oncologic risk, many patients harbor more aggressive disease in nonindex lesions, highlighting the limitations of relying on size alone for managing sporadic multifocal RCC.