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5 slides generated from the cancer page, with a quiz from the open benchmark and speaker notes that cite the sources. Arrow keys move between slides; Print gives one slide per page.
Metaplastic breast cancer is a rare form in which part of the tumour has changed into another tissue type, such as squamous skin-like cells, spindle cells or bone and cartilage. Most are triple-negative and they do worse than other triple-negative cancers, resisting chemotherapy; the low-grade forms are an exception with an excellent outlook.
Metaplastic breast cancer is defined by the histological presence of at least two cellular types, typically epithelial and mesenchymal components, and the WHO classification (5th edition, 2019) lists low-grade adenosquamous carcinoma, fibromatosis-like metaplastic carcinoma, squamous cell carcinoma, spindle cell carcinoma, metaplastic carcinoma with heterologous mesenchymal differentiation (chondroid, osseous) and mixed forms (Tan 2020; Cserni 2020). It carries a triple-negative phenotype yet a worse prognosis and shorter survival than triple-negative disease of no special type, with recurrent alterations in epithelial-to-mesenchymal transition, EGFR amplification, PI3K/Akt, Wnt/beta-catenin and cell-cycle pathways, and no standardised treatment guideline of its own (Reddy 2020). In the National Cancer Data Base, five-year overall survival was 72.7 percent for metaplastic against 87.5 percent for non-metaplastic disease overall and 71.1 against 77.8 percent among triple-negative patients; within metaplastic disease receptor status did not change survival (hazard ratio 1.16); patients more often had mastectomy (59.0 against 44.9 percent), chemotherapy (74.1 against 43.1 percent) and axillary dissection, and more often had negative nodes (20.0 against 10.6 percent); chemotherapy (hazard ratio 0.69) and radiotherapy (0.52) were associated with better survival, axillary dissection with worse (Ong 2018). The claudin-low intrinsic subtype has a high frequency of metaplastic differentiation (Prat 2010). Two members of the family are indolent: fibromatosis-like metaplastic carcinoma and low-grade adenosquamous carcinoma, which the European Working Group for Breast Screening Pathology lists among the triple-negative special types unlikely to benefit from chemotherapy (Cserni 2021).
| Setting | Approach | Guideline |
|---|---|---|
| Early disease | Surgery and radiotherapy, with chemotherapy as for triple-negative disease of no special type; chemotherapy and radiotherapy were associated with better survival in the national database, and axillary dissection was not. Low-grade adenosquamous and fibromatosis-like forms are treated by surgery alone in the European working group's consensus. | not mapped |
| Advanced disease | As for metastatic triple-negative disease (pembrolizumab where PD-L1 positive, TROP2 ADCs); response to chemotherapy is poorer than in other triple-negative cancers. | not mapped |