Characteristics and treatment of metaplastic breast cancer: analysis of 892 cases from the National Cancer Data Base.

Background: Metaplastic breast cancer (MBC) is characterized by various combinations of adenocarcinoma, mesenchymal, and other epithelial components. It was officially recognized as a distinct pathologic diagnosis in 2000. With few published reports, we hypothesized that MBC may have markedly different characteristics at presentation than typical infiltrating ductal carcinoma (IDC) and may be managed differently.

Methods: Data from patients with MBC and IDC reported to the National Cancer Database from January 2001 through December 2003 were reviewed for year of diagnosis, patient age, race/ethnicity, tumor size, nodal status, American Joint Committee on Cancer (AJCC) stage, tumor grade, hormone receptor status, and initial treatment, and were analyzed statistically by the Pearson chi(2) test.

Results: A total of 892 patients with MBC and 255,164 patients with IDC were identified. The group with MBC was older (mean age, 61.1 vs. 59.7 years; P = .001), had a significantly increased proportion of African American (14.1%, 126 of 892, vs. 10.2%, 25,900 of 255,164; odds ratio [OR], 1.455, P = .001) and Hispanic patients (5.5%, 49 of 892 vs. 3.9%, 9,947 of 255,164; OR, 1.817, P = .001), had fewer T1 tumors (29.5% vs. 65.2%), more N0 tumors (78.1% vs. 65.7%, OR, .5, P = .001), more poorly or undifferentiated tumors (67.8% vs. 38.8%), and fewer estrogen receptor-positive tumors (11.3% vs. 74.1%, OR, 22.4, P = .001) than the IDC group. Patients with MBC were treated with breast-conserving surgery less frequently than patients with IDC (38.5% vs. 55.8%, OR, 2.0, P = .001) because of the larger tumor size. Chemotherapy was used more often for patients with MBC (53.4% vs. 42.1%, OR, 1.6, P = .001) because of more advanced AJCC stage.

Conclusions: MBC is a rare tumor with different characteristics than IDC: it presents with larger tumor size, less nodal involvement, higher tumor grade, and hormone receptor negativity. Patients with MBC are treated more aggressively than IDC (more often with mastectomy and chemotherapy) because of a higher stage at presentation, but are being treated by the same principles as IDC. Follow-up will determine the long-term results of the current treatment.