描述据我们所知，首例公认的具有 PiMHEC 样表型的三阴性乳腺癌 (TNBC) 病例。 毛母质样高级别子宫内膜样癌（PiMHEC）是一种具有不同分化程度的高级别癌，类似于最近在子宫内膜和卵巢中描述的皮肤毛母质癌。作为参考，PiMHEC 的相关特征包括 (1) 高级基底细胞至鳞状细胞形态，存在鬼细胞； (2) 尽管有鳞状外观，但仅局部表达 p63 和/或 p40； (3) CTNNB1突变，伴有弥漫性β-catenin表达异常和LEF1和/或CDX2表达异常； (4) 位点特异性标记物（即 PAX8、ER）丢失。在此，我们报告一例具有 PiMHEC 样表型的三阴性乳腺癌 (TNBC) 病例的组织学、免疫表型和分子遗传学特征。肿瘤紧邻 HER2、雄激素受体 (AR)、GATA3 常规 3 级浸润性导管癌 (IDC)，仅膜性 β-连环蛋白表达。 PiMHEC 样成分具有子宫内膜 PiMHEC 的所有上述形态和免疫表型特征，但丢失了 GATA3 和 AR，而不是 PAX8 和 ER。 对两种肿瘤成分进行的分子分析表明，共有 TP53 点突变和仅限于 PiMHEC 样成分的外显子 3 CTNNB1 突变，这意味着与 CTNNB1 的二次获得存在克隆关系。新辅助化疗后，HER2 常规成分已完全消退，但 PiMHEC 样成分几乎没有反应。该病例表明，PiMHEC 样表型可能被视为 TNBC 的一种形式，可以从传统 IDC 发展而来，但失去了位点特异性生物标志物、CTNNB1 突变的获得以及对传统化疗的耐药性。© 作者 2024。由牛津大学出版社代表美国临床病理学会出版。版权所有。如需商业重复使用，请联系 reprints@oup.com 获取转载和转载的翻译权。所有其他权限都可以通过我们网站文章页面上的权限链接通过我们的 RightsLink 服务获得 - 如需更多信息，请联系journals.permissions@oup.com。

To describe what is, to our knowledge, the first recognized case of a triple-negative breast carcinoma (TNBC) with a PiMHEC-like phenotype. Pilomatrix-like high-grade endometrioid carcinoma (PiMHEC) is a high-grade carcinoma with divergent differentiation resembling cutaneous pilomatrix carcinoma that was recently described in the endometrium and ovary. For reference, pertinent features of PiMHEC include (1) high-grade basaloid to squamoid morphology with the presence of ghost cells; (2) only focal p63 and/or p40 expression despite a squamoid appearance; (3) CTNNB1 mutation, accompanied by diffusely aberrant β-catenin expression and LEF1 and/or CDX2 expression; and (4) loss of site-specific markers (ie, PAX8, ER).Here we report the histologic, immunophenotypic and molecular genetic features of a case of a triple-negative breast carcinoma (TNBC) with a PiMHEC-like phenotype.The tumor developed immediately adjacent to a HER2+, androgen receptor (AR)+, GATA3+ conventional grade 3 invasive ductal carcinoma (IDC) with only membranous β-catenin expression. The PiMHEC-like component had all of the above-noted morphologic and immunophenotypic features of endometrial PiMHEC but with loss of GATA3 and AR rather than PAX8 and ER. Molecular analysis performed on both tumor components demonstrated a shared TP53 point mutation and an exon 3 CTNNB1 mutation restricted to the PiMHEC-like component, implying a clonal relationship with secondary acquisition of CTNNB1. Following neoadjuvant chemotherapy, the HER2+ conventional component had completely resolved, but the PiMHEC-like component had very little response.This case demonstrates that a PiMHEC-like phenotype may be seen as a form of TNBC that can develop from conventional IDC, with loss of site-specific biomarkers, acquisition of CTNNB1 mutation, and resistance to conventional chemotherapy.© The Author(s) 2024. Published by Oxford University Press on behalf of American Society for Clinical Pathology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.