Prognostic significance of the sub-classification of stage pT3a renal tumors by perinephric and sinus fat invasion

In the current Tumor-Node-Metastasis (TNM) classification system for renal cell carcinoma (RCC), both perinephric fat invasion (PFI) and renal sinus fat invasion (SFI) are classified at the T3a stage. However, their associated prognoses are clinically controversial. The present study proposes a new sub-classification criterion for pathological T3a (pT3a) RCC with SFI or PFI to resolve this dispute. Data were collected from consecutive records of 2,765 patients with T1a renal cancer, who had undergone partial nephrectomy (PN) between 2001 and 2015 at one of four hospitals. Among these patients, 127 cases were diagnosed with stage pT3a RCC with SFI or PFI, according to final pathological examination. The pathological characteristics, clinical data and follow-up observations were analyzed. Of the 127 patients, with an average follow-up duration of 56 months (range, 15-60 months), 17 cases of tumor recurrence were found. After analysis of the pathological findings, the following new sub-classification criteria was proposed for pT3a RCC with SFI or PFI: i) Type A, renal tumor invades the pseudo-capsule and contacts with the perinephric adipose tissues directly (3 recurrences out of 57 patients); ii) type B, tumor protrudes into the perinephric adipose tissues like a tongue (4 recurrences out of 29 patients); and iii) type C, tumor nodules distribute in perinephric adipose tissues (10 recurrences out of 41 patients). There was statistically significant difference between the three subtypes in terms of recurrence rate (P=0.023). In conclusion, controversies remain in the current TNM classification system for pT3a RCC. The present study added to the available data and found that pT3a RCC with tumor nodules in perinephric adipose or/and with an irregular tumor protruding into adipose tissues showed a higher recurrence rate. Thus, it is recommended that pT3a RCC should be carefully analyzed and should be considered differently to other stages of RCC.