Characteristics and Outcomes of T1a Renal Cell Carcinoma Presenting with Metastasis.

Objectives: The incidence of renal cell carcinoma (RCC) has been rising, largely due to increased incidental detection from widespread imaging. Although synchronous distant metastasis (SM) with a primary renal tumor measuring <4 cm (cT1a) is uncommon, its presence may influence survival outcomes and the utility of cytoreductive nephrectomy. We sought to investigate clinical characteristics, metastatic patterns, treatments, and survival outcomes of patients with T1a RCC.

Methods: All patients aged ≥18 years diagnosed with RCC between 2004 and 2019 were extracted from the National Cancer Database. The Cochran-Armitage test was used for trend analysis, while multivariable analyses were conducted to identify variables associated with SM and to assess the impact of cytoreductive surgery on mortality across isolated metastatic sites. Kaplan-Meier analysis was performed to compare survival outcomes.

Results: A total of 263,911 individuals diagnosed with T1a RCC were analyzed in the study. Among them, 114,661 patients (43.4%) were classified as having cT1a tumor stage, and of these patients with cT1a RCC, 2275 (2.0%) exhibited SM. The proportion of SM cT1a was 3.39% in 2004 and 2.08% in 2019, with an Average Annual Percent Change (AAPC) of -0.037% ( = 0.830). The most common sites of metastasis were bone (59%), followed by lung (35%), liver (16%), and brain (12%). Resection of the primary tumor and receipt of systemic therapy were significantly associated with reduced mortality among all metastatic sites, especially in individuals with lung-only metastases (HR = 0.02, = 0.013). Metastasectomy was associated with improved survival in patients with brain-only metastases (HR = 0.26, = 0.006) but did not demonstrate the same benefit in patients with bone-, lung- or liver-only metastases. The worst 5-year OS rate was observed in cases with metastasis to multiple sites, whereas isolated metastases had similar survival rates ( < 0.0001). Our findings are limited by retrospective study design.

Conclusions: This comprehensive analysis of T1a RCC patients reveals that while synchronous metastasis is relatively uncommon (2.0%), it presents significant clinical challenges, with bone as the most common metastatic site, contrasting with the typical lung predominance in larger tumors. Primary tumor resection showed survival benefit in patients with isolated metastases, especially for lung-only metastasis. These findings highlight the heterogeneous nature of tumor biology in small renal masses and underscore the importance of tailored, multimodal treatment strategies for the effective management of SM T1a RCC.