A Systematic Review With Individual Patient Data Meta-analysis on Characteristics and Outcomes of Patients With Metaplastic Breast Carcinoma.

Metaplastic breast carcinoma (MBC) is a rare disease for which there is limited evidence from large prospective trials. This systematic review analyzed the characteristics, treatments, and outcomes of MBC patients reported in the literature until October 2024. PubMed and Web of Science were searched systematically for case reports or case series on MBC using predefined search terms according to PRISMA guidelines for systematic reviews (last search: October 2024; registered with Prospero: ID CRD42022356323). Three hundred eighty-four English-language articles (1978-2024) reporting on 491 patients diagnosed with MBC were included. The median age at diagnosis was 53 years (range, 15-98 years). The median overall survival (OS) was 75.0 months, and median progression-free survival (PFS) was 36.0 ± 13.6 months (standard error). The most frequent locations of recurrence were the lung and local areas. Univariate analysis revealed that increasing tumor size, publication before the year 2000, lymphadenopathy, metastasis, distant recurrence, and histopathological subtype significantly influenced OS (P < .05). Distant recurrence, metastasis, and year of publication before 2000 were identified as independent predictors of survival through multivariate Cox regression (P < .05). Tumor size, the proliferation index (Ki-67), and histopathological subtype significantly influenced PFS (P < .05). Adjuvant therapy improved OS and PFS in patients with localized disease (M0) (P < .05). This is the first systematic analysis of MBC, showing heterogeneous treatment patterns for localized and metastatic disease. Intensive multimodal therapy may improve tumor control and warrants further investigation. The significance of these results is limited by their retrospective nature and the inhomogeneity of single-case reports.