Breast Cancer Subtypes and Incidence of Brain Metastases in the SEER Database

Abstract

<h3>Purpose/Objective(s)</h3> Despite the recognition that women with triple-negative (TNBC) and HER2+ breast cancer have a higher risk of developing brain metastases than other subtypes of breast cancer, the recently updated NCCN guidelines for breast cancer do not recommend MR imaging of the brain in women with either primary or metastatic breast cancer (of any type) unless there are neurologic signs/symptoms suspicious for brain metastases. We investigated the relative distribution of synchronous and metachronous brain metastases over the past decade. <h3>Materials/Methods</h3> We evaluated the Surveillance, Epidemiology, and End Results (SEER) SEER-18 database for breast cancer patients diagnosed from 2010-2017. Female patients with complete data regarding presence of brain metastases, stage, breast cancer subtype, and survival were selected. Relative frequencies of subtypes at diagnosis for all patients (localized and metastatic), synchronous brain metastases, and metachronous brain metastases were calculated. Metachronous brain metastases were defined as patients who had both a primary and localized breast cancer diagnosis and subsequent brain metastases diagnosis both recorded in SEER as separate entries from different years with the same patient identifying number. <h3>Results</h3> We found 394,153 patients who fit criteria. The percent incidence of brain metastases at diagnosis did not change significantly over the years examined (range 0.33-0.39%, chi-squared p=0.59) Overall frequency of brain metastases was 0.67%, 0.22%, 1.17%, and 0.71% for luminal B, luminal A, HER2+, TNBC, respectively (chi-squared p<0.001). Relative frequency of breast cancer subtypes among all cases, synchronous brain metastases, and metachronous brain metastases showed increasing proportion of patients with TNBC. Only 26 patients were found that had metachronous brain metastases in the database. Of those patients, 38.5% had TNBC. <h3>Conclusion</h3> This SEER-based analysis shows that although presentation with synchronous brain metastases is relatively balanced across all molecular subtypes, metachronous brain metastases are most commonly seen in TNBC patients, perhaps indicative of the prevalence of occult brain metastases at presentation in patients with TNBC. Unfortunately, metachronous brain metastases are not robustly recorded in SEER. Better data is needed on the prevalence of brain metastases at the time of initial diagnosis and when systemic progression occurs in TNBC patients.