The unique luminal staining pattern of cytokeratin 5/6 in adenoid cystic carcinoma of the breast may aid in differentiating it from its mimickers

Breast lesions with myoepithelial phenotype

Myoepithelial cells (MECs) constitute a continuous layer of cells surrounding the breast glands, localised between the epithelial cells (ECs) and the basal membrane. MECs play important roles in normal mammary gland as they produce basal membrane and stimulate secretion. During neoplastic transformation, MECs act as a barrier preventing stromal invasion. MECs themselves can undergo a great variety of changes, ranging from hyperplastic to metaplastic, to neoplastic, and giving rise to a wide spectrum of morphological pictures sometimes difficult to interpret on routine diagnoses. Several benign and malignant breast tumours can present features of MECs differentiation. As these latter tumours are quite infrequent, the purpose of the present study is to offer a review of the morphological spectrum of MECs lesions, with correlations to prognosis.

Adenoid Cystic Carcinoma of the Breast: Radiologic-Pathologic Correlation

Adenoid cystic carcinoma (ACC) is an uncommon malignancy occurring most frequently in the salivary glands. Breast ACC is rare. Pain is common at the site of ACC; otherwise, presentation is similar to other primary breast cancers. Adenoid cystic carcinomas classically lack calcifications; the imaging manifestations of ACC are otherwise highly variable, likely related to multiple pathologic growth patterns. While ACC in other regions of the body tends to be more aggressive, ACC involving the breast typically has less aggressive biologic characteristics. Classic-type breast ACC has a lower tendency to recur locally with radiation, metastasize to regional lymph nodes, and spread to other parts of the body. Perineural spread of disease can be seen but is not common. The rarer solid basaloid-type has a higher tendency for local or distant spread and recurrence. Although ACC is usually triple receptor-negative (estrogen receptor, progesterone receptor, human epidermal growth factor-2 receptor), the indolent nature of this tumor dictates its management. With classic-type ACC, the inclusion of axillary surgery has no consensus and the use of chemotherapy or hormonal therapy is rare. Axillary nodal surgery and chemotherapy are often included in management of the more aggressive solid basaloid-type. An understanding of the breast imaging, histopathology, and clinical course is key for appropriate treatment and follow-up of ACC.

MYB RNA In Situ Hybridization Is a Useful Diagnostic Tool to Distinguish Breast Adenoid Cystic Carcinoma From Other Triple-negative Breast Carcinomas

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.

Special Histologic Type and Rare Breast Tumors - Diagnostic Review and Clinico-Pathological Implications

Breast cancer is the most common malignant tumor in females. While most carcinomas are categorized as invasive carcinoma, no special type (NST), a diverse group of tumors with distinct pathologic and clinical features is also recognized, ranging in incidence from relatively more common to rare. So-called "special histologic type" tumors display more than 90% of a specific, distinctive histologic pattern, while a spectrum of tumors more often encountered in the salivary gland may also arise in the breast. Metaplastic carcinomas can present diagnostic challenges. Some uncommon tumors harbor pathognomonic genetic alterations. This article provides an overview of the key diagnostic points and differential diagnoses for this group of disparate lesions, as well as the salient clinical characteristics of each entity.

Low-risk triple-negative breast cancers: Clinico-pathological and molecular features

Triple-negative breast cancers (TNBC) comprise biologically and clinically heterogeneous diseases characterized by the lack of hormone receptors (HR) and HER2 expression. This subset of tumors accounts for 15-20% of all breast cancers and pursues an ominous clinical course. However, there is a spectrum of low-risk TNBCs with no/minimal metastatic potential, including the salivary gland-type tumors, those with extensive apocrine differentiation and/or high tumor-infiltrating lymphocytes, and small-sized, early-stage (pT1a/bN0M0) TNBCs. De-escalating the treatment in low-risk TNBC, however, is not trivial because of the substantial lack of dedicated randomized clinical trials and cancer registries. The development of new diagnostic and/or prognostic biomarkers based on clinical and molecular aspects of low-risk TNBCs would lead to improved clinical treatment. Here, we sought to provide a portrait of the clinicopathological and molecular features of low-risk TNBC, with a focus on the diagnostic challenges along with the most important biological characteristics underpinning their favorable clinical course.

Breast adenoid cystic carcinoma arising in microglandular adenosis: A case report and review of literature

BACKGROUND

Breast adenoid cystic carcinoma (AdCC) is a rare invasive carcinoma composed of epithelial and myoepithelial cells. Microglandular adenosis (MGA) is a rare benign proliferative lesion consisting of small, uniform, and round glands formed by a single layer of epithelial cells and basement membrane without a myoepithelial cell layer. MGA may progress to atypical MGA and carcinoma arising in MGA. Among various invasive carcinomas from MGA, AdCC has been rarely reported. Here, we report a case of AdCC arising in MGA.

CASE SUMMARY

A 59-year-old woman was diagnosed with a newly developed density on a routine mammogram. The density was similar to or slightly lower than that of the breast parenchyma. Sonography showed an irregular mass with a slightly higher echo than that of fat. Magnetic resonance imaging showed an irregular mass with a similar T1 signal intensity and a slightly higher T2 signal intensity compared to muscles or the breast parenchyma. The lesion showed heterogeneous internal enhancement with an initially slow and delayed persistent enhancing pattern. Microscopically, the tumor was composed of invasive AdCC, in situ AdCC, and MGA. AdCC is composed of basaloid and ductal epithelial cells forming cribriform or solid sheets, or haphazardly scattered small cribriform or tubular glands. MGA showed small glands with a single epithelial lining and retained lumen. S-100 staining was strongly positive in MGA area. The patient underwent breast-conserving surgery with sentinel lymph node biopsy.

CONCLUSION

Breast AdCC arising in MGA showed unique imaging findings that was different from usual invasive cancer.

Cutaneous Adnexal Cylindroma of Breast: Epithelial Immunoreactivities for GATA-3, Mammaglobin, and E-Cadherin Do Not Equate to a Mammary Ductal Neoplasm

Cylindromas are benign epithelial neoplasms derived from cutaneous eccrine adnexal structures. These tumors are most commonly encountered on the head, neck, and scalp of older women. In rare instances, solitary cylindromas may arise at other body sites. In the current case, a cylindroma of the skin of the breast was diagnosed by complete excision. Immunohistochemical studies confirmed the tumor cells to be immunoreactive with cytokeratin AE1/3, cytokeratin 5/6, cytokeratin 7, p63, and SOX10. The neoplastic cells were also noted to be immunoreactive with markers typically expected to be positive in ductal epithelium of the breast including GATA3, mammaglobin, and E-cadherin. The case emphasizes the importance of correlating clinical setting, imaging studies, patient history, and careful microscopic evaluation in arriving at an accurate diagnosis. This case also illustrates the point that not all “breast” tumors that are confirmed to be positive for GATA3, mammaglobin, and E-cadherin are derived from mammary ducts.