Abstract: Background　Renal cell carcinoma is one of the most common malignant tumors of the urinary system, and tumor staging is a crucial basis for prognostic assessment. However, significant heterogeneity exists among patients with pathologically staged T3a renal cell carcinoma according to different invasion subtypes. Objective　To investigate the prognostic values of different invasion subtypes in patients with pathological T3a renal cell carcinoma (RCC). Methods　Clinical data about 1 014 patients with pathological T3a RCC who were treated at the Department of Urology of PLA General Hospital from January 2006 to December 2024 were retrospectively analyzed. According to pathological findings, patients were categorized into an isolated invasion subtype group or a combined invasion subtype group based on tumor invasion into one or more of the following structures: perirenal fat, renal sinus fat, renal vein or its segmental branches, pelvicalyceal system. The combined invasion subtype group was further categorized according to the number of invaded sites into 2, 3, and 4 site invasion subgroups. Cancer-specific survival (CSS), overall survival (OS), and disease-free survival (DFS) were compared among patients with different invasion subtypes, and independent prognostic factors were identified.Results　A total of 1 014 patients (748 males, 266 females) with pathological T3a RCC were included in this study, with a mean age of (57.0 ± 12.1) years. Of these, 757 cases were classified into the isolated invasion subtype group, including 163 cases with perirenal fat invasion, 313 cases with renal sinus fat invasion, 129 cases with renal vein or its segmental branches invasion, and 152 cases with pelvicalyceal system invasion, while 257 patients were classified into the combined invasion subtype group. Compared with the isolated invasion subtype group, patients in the combined invasion subtype group were significantly older (58.5 ± 12.4) years vs (56.6 ± 10.7) years, P=0.013, had larger maximum tumor diameters (7.39 ± 2.85) cm vs (5.86 ± 3.13) cm, P＜0.001, underwent radical nephrectomy more frequently (98.1% vs 89.3%, P＜0.001), showed a higher proportion of WHO/ISUP grade 3 – 4 tumors (35.2% vs 20.1%, P＜0.001). Kaplan – Meier survival analysis demonstrated that patients with a combined invasion subtype had significantly worse CSS, OS and DFS than those with an isolated invasion subtype (all P＜0.001). Within the combined invasion subtype group, CSS (P=0.042), OS (P=0.048), and DFS (P＜0.001) progressively decreased with an increasing number of invaded sites. Multivariate Cox regression analysis showed that combined invasion subtype remained an independent prognostic factor for CSS and DFS after adjustment for age, tumor size, histological subtype, WHO/ISUP nuclear grade and surgery year (CSS: HR=2.228, 95% CI: 1.506 - 3.297, P=0.001; DFS: HR=2.020, 95% CI: 1.535 - 2.660, P＜0.001).Conclusion　In patients with pathological T3a RCC, no significant prognostic differences are identified among individual invasion subtypes. A combined invasion subtype indicates a poorer prognosis, and both invasion subtype and the number of invaded sites may serve as important prognostic indicators for patients with pathological T3a RCC.