Introduction: Metachronous and synchronous metastases from small renal masses (SRM) are often grouped in research, but may in fact be very distinct biologic entities. Identification of clinical and pathologic predictors of metachronous SRM metastasis will be useful to counsel clinically localized SRM patients regarding active surveillance vs. definitive treatment. We provide the first study to our knowledge comparing features of metachronous vs. synchronous mSRM patients.
Methods: A nephrectomy patient database at a single National Comprehensive Cancer Network institute was retrospectively queried to identify all patients undergoing partial or radical nephrectomy between 1998-2019 for renal cell carcinoma (RCC) with SRM defined as pathological tumor size =4 cm. SRM patient metastasis (mSRM) was classified as either synchronous (smSRM, diagnosed prior to or at nephrectomy) or metachronous (mmSRM, after nephrectomy). Variables compared between smSRM and mmSRM patients included preoperative clinical features, surgical pathology, location(s) of metastasis, and survival time from metastasis.
Results: Among 501 SRM patients identified, 28 (5.6%) were diagnosed with metastasis, including 14 smSRM (2.8%) and 14 mmSRM (2.8%). Male gender, age, tumor size, Fuhrman grade, pT stage and worse renal function were significantly associated with mSRM. Metachronous metastases occurred at a median (mean, range) of 34 (47, 2-155) months after surgery. A striking gender association was observed for mmSRM (but not smSRM). Specifically, all 14 mmSRM cases were male, and no female SRM patient has developed postoperative metastasis. mmSRM patients were also less likely to have non-clear cell histology compared to smSRM patients (14% vs. 35%), with 2/129 (1.5%) non-ccRCC patients developing postoperative metastasis compared to 12/371 (3.2%) ccRCC patients. smSRM patients had a very aggressive clinical course, with a median time from surgery to death of 10 months compared to 29 months for mmSRM patients, although median time from metastasis to death was similar (13 vs 15 months, respectively). smSRM tended to present more often with multiple metastatic sites (79% vs. 57%).
Conclusions: This study reveals clinical and histologic differences between smSRM and mmSRM that support these groups as likely distinct biologic entities. Female gender and non-clear cell histology may be protective against metachronous RCC, which has implications for both active surveillance and postoperative surveillance regimens. Source of