Introduction: Metaplastic breast cancer (MBC) is considered rare and aggressive. We examined the epidemiology of and prognostic factors for MBC and investigated the effect of contralateral prophylactic mastectomy (CPM), because neither had been thoroughly examined previously.
Methods: We obtained data from the Surveillance, Epidemiology, and End Results (SEER)-18(2000-2018) for epidemiological and survival analysis.
Results: The age-adjusted incidence per 100,000 persons of MBC increased significantly from 0.12 to 0.35 [annual percent change (APC):2.95%, 95% confidence interval [CI], 1.73-4.19]. The incidence-based mortality increased from 0.01 to 0.12 (APC: 5.01%, 95% CI: 2.50-7.58). The incidence of MBC patients who underwent CPM significantly increased from 0.003 to 0.039 with an APC of 10.96% (95%CI, 7.26-14.78). Older patients and those with higher T classification were less likely to receive CPM. The multivariate Cox model showed that CPM was not an independent predictor of good prognosis for both overall survival (OS) and breast cancer-specific survival (BCSS) (pre-propensity score matching (PSM): OS: P = 0.331; BCSS: P = 0.462. post-PSM: OS: P = 0.916; BCSS: P = 0.967). Subgroup analysis showed that CPM still did not provide a survival benefit to any risk groups.
Conclusion: In this study, we demonstrated that the incidence and incidence-based mortality of MBC have increased over the past decades. Although the number of MBC patients who underwent CPM has significantly increased recently, CPM did not confer a survival benefit compared with unilateral mastectomy, indicating that the decision to undergo CPM should be considered carefully.
Keywords: Contralateral prophylactic mastectomy; Incidence; Incidence-based mortality; Metaplastic breast cancer; SEER.
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