Studying the association between breast cancer and renal cell carcinoma

Purpose There are case reports of patients with both primary breast cancer (BC) and renal cell carcinoma (RCC). We explore the association between these two malignancies using SEER population data and our institutional records. Methods We studied the association between BC and RCC in the 2000–2016 Surveillance, Epidemiology, and End Results (SEER) database. We then reviewed our hospital records of patients with both BC and RCC and collected information including personal and family history of cancers, genetic testing, and patient outcomes. Results Of the 813,477 females diagnosed with BC in the SEER database, 1914 later developed RCC. The risk of developing RCC was significantly increased within the first 6 months, 7–12 months, and 1–5 years following BC diagnosis with standardized incidence ratios (SIRs) of 5.08 (95% CI 4.62–5.57), 2.09 (95% CI 1.8–2.42), and 1.15 (95% CI 1.06–1.24), respectively. Of 56,200 females with RCC, 1087 later developed BC. The risk of developing BC following RCC was elevated within the first 6 months (SIR of 1.45 [95% CI 1.20–1.73]). For our hospital patients, 437 had both BC and RCC. 427 (97.71%) were female, and 358 (81.92%) were white, and breast cancer was diagnosed before RCC in 246 (56.3%) patients. There were 15 germline mutations in those with genetic testing. Conclusion Our findings suggest that BC patients are at higher risk of developing RCC and vice versa. BC tended to precede RCC, and patients frequently had personal histories of other malignancies and a family history of cancer, particularly, BC.