10-year mastectomy trends among breast cancer phenotypes: A national cohort study.

Abstract

584 Background: Breast cancer tumor phenotype has prognostic value with triple negative (TN) cancers having higher rates of distant metastases early. While tumor phenotypes are prognostic, published data demonstrates that the choice of local therapy does not affect this predisposition or affect survival. This study was performed to determine whether mastectomy is being performed more frequently for TN or HER2+ phenotypes, relative to hormone receptor positive (HR+) phenotypes despite the lack of benefit this should provide. Methods: Data from the National Cancer Database (NCDB) was analyzed from 2010 through 2019 to assess mastectomy trends and associations with patient and tumor characteristics. Women with invasive breast cancer were included. Women with Stage IV disease were excluded. Patients were categorized as mastectomy or breast conservation surgery. Patient and tumor characteristics were compared across groups using chi-square and Wilcoxon rank sum tests, and a multivariable logistic regression model was fit to assess the association between mastectomy and tumor phenotype controlling for patient and tumor characteristics. Results: 543,590 patients were evaluated. 173,380 (31.9%) patients underwent mastectomy, and 370,210 (68.1%) patients underwent breast conservation surgery. Mean age at diagnosis was 56. There were 425,174 HR+, 64,960 HER2+, and 53,456 TN tumors. The proportion of patients undergoing mastectomy peaked in 2013 at 36.14% before declining. Compared to HR+, HER2+ patients were more likely to undergo mastectomy, OR 1.39 p < 0.0001 (95% CI 1.35 – 1.43); however, there was no significant difference in mastectomy between HR+ patients and TN patients. Compared to whites, black patients were less likely to undergo mastectomy, OR 0.71 p < 0.0001 (95% CI 0.69 – 0.74), and individuals of Hispanic ethnicity less likely to undergo mastectomy, OR 0.92 p < 0.0001 (95% CI 0.89 – 0.95). Compared to private insurance, Medicare had a greater association with mastectomy, OR 1.2 p < 0.0001 (95% CI 1.18 – 1.23). There was no significant difference between other forms of insurance (Medicaid, other government insurance, no insurance) and private insurance. Education and income were not associated with different frequencies of mastectomy. Patients with higher comorbidity scores were more likely to undergo mastectomy. Conclusions: Mastectomy rates have been declining since 2013 at CoC centers. While TN breast cancer is not associated with increased mastectomy percent, mastectomy continues to be performed more frequently for HER2+ positive phenotype when adjusting for tumor and patient characteristics. These data suggest a need for education about HER2 positive phenotype due to a possible lack of understanding about the why such tumors pose a risk, and the role of local therapy in treating them.