T1a Renal Cell Carcinoma With Metastasis: Japanese Society of Renal Cancer Retrospective Multi-institute Results.

BACKGROUND/AIM: Small renal cell carcinomas (sRCC) have drastically increased in recent years. Considering that sRCC have heterogeneous biology, it would be clinically relevant if specific clinical or pathological parameters could predict sRCC metastasis. In the present study, we aimed to assess the clinicopathological factors of pathologic T1a RCC (pT1a RCC) with or without metastasis to explore factors predicting metastasis. PATIENTS AND METHODS: The present study included 198 patients with pT1a RCC who underwent radical or partial nephrectomy at fifteen institutions belonging to the Japanese Society of Renal Cancer, between1985 and 2017. Clinicopathological parameters, including age, sex, tumour size, tumour side, histological subtype, histological nuclear grade, lymphovascular invasion, and histological growth patterns, were analysed. RESULTS: Fuhrman grade 3 or 4 tumours and infiltrative tumour growth patterns were significantly higher in patients with metastasis than in those without. The most common site of synchronous metastasis was the bone in patients with pT1a RCC (65.4%), whereas for patients with post-surgery metachronous metastasis (46.2%), it was the lungs. CONCLUSION: Histological growth pattern and nuclear grade are vital for predicting metastasis in pT1a RCC, suggesting careful long-term follow-up for such patients.