Neoadjuvant Chemotherapy for Metaplastic Breast Cancer: Response Rates, Management, and Outcomes

Introduction: Neoadjuvant chemotherapy (NAC) for breast cance has not been well studied for metaplastic breast cancer (MBC), a rare but aggressive type of breast cancer. Materials and Methods: The National Cancer Database was queried (2004-2017) for females with cM0 MBC who received NAC and definitive surgery with a pathologic staging record. Statistics included Kaplan-Meier overall survival (OS) analysis, multivariable logistic regression, and Cox proportional hazards modeling. Results: Of 903 MBC patients, 88 (9.8%) experienced a pathologic complete response (pCR). The vast majority of ypT0 cases were initially cT1-2. On multivariable logistic regression, cT1 disease was a single factor that was associated with pCR. The majority of patients with MBC undergoing pCR still underwent mastectomy (62.5%) and sentinel node biopsy (67.1%). Axillary dissection was more common in non-pCR cases (49.3% vs. 29.6%, P =.001). The 5 year OS difference amongst MBC patients between pCR vs. RCB1-3 was significant (93 vs. 63%, P <.001). There was no difference observed between MpBC with pCR and non-MpBC invasive ductal carcinoma (IDC) with pCR (93 vs. 93%), with pCR (P >.05 for all molecular subtypes). Conclusion: This study confirms that response rates of MBC to NAC are low, with pCR being relatively infrequent. However, early-stage MBC may be more likely to achieve pCR. These findings combined with emerging research on identifying favorable histopathologic subtypes of MBC may better elucidate subsets with higher proclivity for pCR, especially because these patients achieve satisfactory survival, comparable to that of IDC with pCR.