Breast adenoid cystic carcinoma (AdCC) has overlapping features with basal-like triple-negative breast carcinoma (TNBC), yet carries a more favorable prognosis, and accurate diagnosis is critical. Like salivary gland AdCC, breast AdCC demonstrates recurrent alterations in the MYB gene. Novel chromogenic RNA in situ hybridization (ISH) for MYB has emerged as sensitive and specific for salivary gland AdCC. Here, we evaluate MYB RNA ISH in invasive ductal carcinomas (IDCs) including basal-like TNBC, and in the histologic mimics ductal carcinoma in situ (DCIS) and collagenous spherulosis. MYB RNA ISH was also performed on previously constructed tissue microarrays containing 78 evaluable IDC, including 30 basal-like TNBC (EGFR⁺ and/or CK5/6⁺), 19 luminal A (ER⁺/HER-2⁻), 12 HER-2⁺ (ER⁻/HER-2⁺), 11 non–basal-like TNBC, and 6 luminal B (ER⁺/HER-2⁺). MYB RNA ISH overexpression was seen in 100% (n=18/18) of primary breast AdCC and 10% (n=8/78) of IDC (P<0.0001). MYB RNA ISH was overexpressed in 37% (n=7/19) of luminal A and 8% (n=1/12) of HER-2⁺ IDC, and in no cases of TNBC or luminal B IDC. The majority (67%, n=8/12) of DCIS and all (n=7) cases of collagenous spherulosis demonstrated overexpression of MYB RNA. MYB gene rearrangement was detected in 67% (n=4/6) evaluable AdCC. Although MYB RNA ISH overexpression cannot be used to distinguish between cribriform DCIS or collagenous spherulosis and AdCC, MYB RNA ISH is absent in basal-like TNBC and rare in ER⁺ or HER-2⁺ IDC. MYB RNA ISH could be a useful, sensitive, and rapid diagnostic adjunct in the workup of a triple-negative carcinoma in the breast.

乳腺腺样囊性癌（AdCC）与基底样三阴性乳腺癌（TNBC）有重叠的特征，但预后更好，准确诊断至关重要。与唾液腺 AdCC 一样，乳腺 AdCC 也表现出MYB基因的反复改变。MYB的新型显色 RNA 原位杂交 (ISH)对唾液腺 AdCC 具有敏感性和特异性。在这里，我们评估了浸润性导管癌 (IDC)（包括基底样 TNBC）以及组织学模拟导管原位癌 (DCIS) 和胶原球增生中的MYB RNA ISH。还在之前构建的含有 78 个可评估 IDC 的组织微阵列上进行了MYB RNA ISH，其中包括 30 个基底样 TNBC（EGFR ⁺和/或 CK5/6 ⁺）、19 个 luminal A (ER ⁺ /HER-2 ⁻ )、12 个 HER- 2 ⁺ (ER ⁻ /HER-2 ⁺ )、11 个非基底样 TNBC 和 6 个 luminal B (ER ⁺ /HER-2 ⁺ )。MYB RNA ISH 过表达在 100% (n=18/18) 的原发性乳腺 AdCC 和 10% (n=8/78) 的 IDC 中观察到 ( P <0.0001)。MYB RNA ISH 在 37% (n=7/19) 的管腔 A 和 8% (n=1/12) 的 HER-2 ⁺ IDC中过表达，并且在 TNBC 或管腔 B IDC 中没有过表达。大多数（67%，n=8/12）DCIS 和所有（n=7）胶原球增生病例均表现出MYB RNA 过度表达。在 67% (n=4/6) 可评估的 AdCC 中检测到MYB基因重排。虽然MYB RNA ISH 过表达不能用于区分筛状 DCIS 或胶原性球状增生和 AdCC，但MYB RNA ISH 在基底样 TNBC 中不存在，在 ER ⁺或 HER-2 ⁺ IDC 中罕见。MYB RNA ISH 可能是乳腺癌三阴性癌检查中有用、灵敏且快速的诊断辅助手段。