Mucinous Cystadenocarcinoma of the Breast: A Clinicopathologic and Molecular Case Report With Literature Review.
Roberta Iozzo, Eugenia Belcastro, Giuseppe Nicolò Fanelli et al.
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Case in brief
A 47-year-old woman with a history of right-breast NST carcinoma developed a lump in the right chest wall near her breast implant. The tumor had a triple-negative phenotype and expressed mammaglobin, GCDFP15 and TRPS1, while keratin 20 and CDX2 were negative. These findings supported a breast origin, and primary mucinous cystadenocarcinoma of the breast was diagnosed. Next-generation sequencing identified several likely pathogenic mutations and an RP1-34H18.1::NAV3 gene fusion. The abstract does not report treatment or clinical outcome.
What made this case unusual
Molecular analysis identified an RP1-34H18.1::NAV3 fusion, which the authors describe as the first reported example identified through comprehensive RNA-based analysis in this tumor type.
Diagnostic / clinical pearl
For a mucinous cystic tumor near a breast implant, immunohistochemistry can help distinguish a primary breast tumor from a gastrointestinal metastasis; here, mammary markers were positive and keratin 20 and CDX2 were negative.