Abstract P1-15-03: Management and outcomes of metaplastic breast cancer
Authors: Thomas H , Horick N , Spring LM , Brachtel EF , Jimenez RB 
Published: February 2018

Purpose/Objectives: Metaplastic breast cancer (MBC) is a rare malignancy composed of both epithelial and mesenchymal components that accounts for less than 1% of primary breast carcinomas. Knowledge of effective management of the disease remains limited. We retrospectively evaluated the treatment and outcomes of patients with MBC from three academic hospitals.

Materials/Methods: Patients diagnosed with MBC between June 2, 1993 and May 6, 2016 were identified. Demographic and clinical variables were extracted via primary chart review. Descriptive statistics were utilized to summarize the patient cohort's clinical course. The Kaplan-Meier method was used to obtain estimates of local control (LC) and survival.

Results: Seventy-six patients were identified with a median follow-up of 7.6 years (range: 0.18-19.9 years). The median age at diagnosis was 54 (range 28-81). About two-thirds of patients (67%, n=51) presented with a palpable mass while the remaining patients were screen-detected via mammogram (32%, n=24). The majority of patients were AJCC-7 stage I (38%, n=29) or stage II (49%, n=37), while 10% (n=8) were stage III and 3% (n= 2) stage IV. About half of tumors (46%, n=35) were subtyped using WHO histologic classification of MBC. Over half of subtyped cases were spindle cell carcinoma (51%, n=18), 17% were matrix-producing carcinoma (n=6), 23% were adenocarcinoma with squamous differentiation (n=8), 6% were carcinosarcoma (n=2), and 3% were mixed (n=1).The majority of patients had triple negative disease (82%, n=62), while 13% (n=10) had HR+/HER2- disease, and 5% (n=4) had HER2+ disease. Most patients had high grade tumors (84%, n=64) and received breast conserving surgery (61%, n=46) while 39% (n=29) had mastectomies. Seventy-six percent (n=58) of patients received chemotherapy and 61% (n=46) received radiation therapy. All HR+ patients received adjuvant endocrine therapy, and 1 patient received immunotherapy. Of patients who received chemotherapy, 78% (n=45) received adjuvant therapy alone, 17% (n=10) neoadjuvant therapy alone, and 5% (n=3) both. Seventy percent (n=41) of chemotherapy regimens included a taxane. Among 74 patients without metastatic disease at presentation, recurrences were observed in 18% (n=13). Most patients recurred distantly (69%, n=9), while the remainder had isolated local recurrences (n=4). Of 9 distant failures, 3 had MBC subtype information and all 3 were spindle cell carcinoma. Of 4 local recurrences, 3 of 4 were adenocarcinoma with squamous cell differentiation and 1 was spindle cell carcinoma. At a median follow-up of 7.6 years, the local recurrence-free survival was 88%, disease-free survival was 80%, and overall survival was 80%. Kaplan-Meier point estimates for remaining free of local recurrence versus distant recurrence were 99% (95% C.I., 90- 100) versus 96% (95% C.I., 87- 99) at 2 years and 88% (95% C.I., 76-94) versus 87% (95% C.I., 75- 93) at 5 years.

Conclusions: MBC is a rare histologic subtype that commonly presents with high-grade disease and triple-negative receptor status. In contrast to other smaller series, local and distant failure rates in this cohort were consistent with non-MBC triple negative cohorts. Additional molecular based research is warranted to further characterize features associated with local and distant failure.

Citation Format: Thomas H, Horick N, Spring LM, Brachtel EF, Jimenez RB. Management and outcomes of metaplastic breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-15-03.