A clinicopathologic analysis of 70 patients with mucinous breast carcinoma

Purpose: Pure mucinous breast carcinomas (PMBC) are rare cancers that are managed per standard breast cancer treatment protocols. In this study, we review the clinicopathologic features, treatment, and outcomes of patients with PMBC treated at our academic cancer center. Methods: We searched institutional pathology databases for patients with histologically confirmed PMBC over a 20-year period (January 1998 - October 2018) who received any portion of clinical care at our institution. Archival pathology slides were re-reviewed to confirm the diagnosis and record pathologic features, including the presence or absence of a micropapillary component. We estimated recurrence free survival (RFS) probabilities using the Kaplan-Meier method and evaluated prognostic factors using Cox regression. Results: A total of 70 cases of PMBC were identified, including 13 with micropapillary features. Median patient age was 65 years (range, 39-94) and approximately 40 % were African American or Asian. The majority of patients had negative lymph nodes (84 %), tumors < 2 cm (79 %), grade I-II (94 %), and hormone receptor positive (99 %) disease, with Ki-67 proliferation indices <= 10 % (54 %). All patients underwent surgery, 50 % received adjuvant radiation therapy, 6 % adjuvant chemotherapy, and 63 % adjuvant hormone therapy. Five-year RFS was 94 % with no identified clinicopathologic or treatment factors significantly affecting survival, including the presence of micropapillary features. Conclusion: We report one of the more diverse single institution series of patients with PMBC based in the United States. This rare breast cancer subtype is associated with a favorable prognosis and may benefit from omission of aggressive standard treatment approaches.