Recurrent Desmoid-Type Fibromatosis of the Breast in a Young Woman With a Monoallelic MUTYH Germline Variant.

Desmoid-type fibromatosis of the breast is an uncommon, low-grade mesenchymal neoplasm with benign histologic features, characterized by locally aggressive growth and a notable tendency for local recurrence. Clinical management is challenging owing to frequent positive surgical margins, a propensity for recurrence, and the absence of standardized treatment guidelines. We report the case of a 34-year-old woman who underwent mastectomy for recurrent breast desmoid-type fibromatosis, in whom a heterozygous germline MUTYH (MutY DNA glycosylase) variant was identified through hereditary cancer panel testing. This case highlights the potential value of comprehensive pathologic assessment and selective germline genetic testing in patients with recurrent breast fibromatosis, which may offer further insight into tumor biology and inform individualized management strategies.