# Metastatic Potential of Very Small (≤2 cm) Renal Cell Carcinoma: Insights from a Single-Center Experience and Review of the Literature

## TL;DR

This study shows that even very small kidney tumors can sometimes spread, highlighting the need for careful evaluation beyond just tumor size.

## Contribution

The paper provides new insights into the metastatic potential of small renal cell carcinomas (≤2 cm) through a single-center analysis and literature review.

## Key findings

- 2.2% of patients with ≤2 cm RCCs experienced aggressive disease, including one with synchronous metastases.
- Literature review identified 16 additional cases of ≤2 cm RCCs with synchronous metastases.
- Tumor size alone is insufficient to exclude aggressive potential in small renal masses.

## Abstract

Background/Objectives: Small renal masses (SRMs) are being detected more often due to the increasing use of imaging techniques. Many of these lesions are benign or grow slowly, but a small proportion can exhibit aggressive behavior. Several reports have shown that synchronous metastases may occur even in small renal cell carcinomas (RCCs). Our aim is to assess the malignant potential and the metastatic risk of very small RCCs (≤2 cm). Methods: We reviewed consecutive patients who underwent partial nephrectomy for SRMs at our tertiary referral center between 2005 and 2024, focusing on those with a maximum pathologic diameter ≤ 2 cm. Clinical and pathological data were collected, and cases with aggressive features were described. In addition, a literature search on the Medline/PubMed database was performed to identify previously published cases of RCC ≤ 2 cm and to assess their risk of synchronous metastases (SM). Results: Among 578 patients who underwent partial nephrectomy, 116 patients (20%) had tumors ≤ 2 cm, 90 (77.5%) of which were malignant, whereas 22.5% were benign (oncocytoma = 13%; angiomyolipoma = 5%). Median age and tumor size were 51 yrs and 1.7 cm, respectively. Histology showed clear cell (72.2%), papillary (20%), chromophobe (6.6%), and mixed (0.9%). Two patients (2.2%) experienced aggressive disease: one with synchronous metastases and one with recurrence and later progression. From the literature, we identified 16 additional cases of RCC ≤ 2 cm with synchronous metastases and found an important heterogeneity of results regarding the metastatic potential of SRMs. Conclusions: Although uncommon, synchronous metastases can occur in RCCs even smaller than 1–2 cm. Reported rates for SM of SRMs across the literature range between 1% and 13%, with higher risk observed in tumors larger than 3 cm, but without an absolute safe cutoff. Tumor size alone is therefore insufficient to exclude aggressive potential. Clinical decision-making should consider histology, grade, patient age, radiologic features, and emerging molecular markers to guide surveillance and treatment in this growing patient population.