Salivary gland-type mammary carcinoma arising in microglandular adenosis: A case report and clinicopathological review of the literature

A case of extensively spreading acinic cell carcinoma of the breast with microglandular features

Acinic cell carcinoma (ACC) is an exceptionally rare type of breast carcinoma with a low-grade morphology and a favorable prognosis. It is postulated to be a type of invasive carcinoma arising in microglandular adenosis (MGA). We report a case of extensively spreading ACC of the breast with MGA-like features. Macroscopically, yellowish nodules were widely distributed throughout the right breast, up to the axilla, without mass formation. Microscopically, the tumor consisted of two distinct carcinoma components: one was multiple nodular lesions showing invasive carcinoma with fused solid nests, and the other was a widely spreading lesion exhibiting MGA-like features with uniform small single glands. Immunohistochemically, both components were negative for ER, PR, and HER2, and expressed EMA, S100 and lysozyme. The distinct morphology and molecular expression indicated ACC. The single glands in the MGA-like area lacked myoepithelial cells but were linearly surrounded by type IV collagen, a basement membrane component. This case supports the hypothesis that ACC and MGA have the same lineage and indicates that ACC is not necessarily a low-grade malignancy and can be aggressive.

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.