Fibromatosis-like metaplastic carcinoma with aggressive metastasis and a TERT promoter mutation: a case report and literature review.

Background: Fibromatosis-like metaplastic carcinoma (FLMCa) is a rare, typically indolent subtype of triple-negative breast cancer. This report presents an exceptional case of FLMCa with an aggressive clinical course, challenging the conventional understanding of its low metastatic potential. Methods: A 57-year-old woman presented with a left breast mass. The diagnosis was confirmed via histopathology and immunohistochemistry. Sanger sequencing was used to investigate potential genetic drivers. Results: Pathological examination confirmed FLMCa, characterized by bland spindle cells and a triple-negative immunophenotype. A genetic analysis revealed a C228T mutation in the telomerase reverse transcriptase (TERT) promoter region. Despite multimodal therapy, including surgery, radiotherapy, and multiple lines of chemotherapy, the patient developed lung metastasis at 5 months and bone metastasis at 15 months post-surgery. Conclusion: This case highlights that a subset of FLMCa may exhibit unexpectedly aggressive behavior and resistance to conventional therapy. The presence of a TERT promoter mutation suggests a potential molecular mechanism for this virulence. Our findings advocate for a re-evaluation of risk stratification in FLMCa and underscore the critical need for vigilant follow-up and molecular profiling to guide future targeted therapy strategies.