Primary acinic cell carcinoma of the breast: a case report with an immunohistochemical and ultrastructural studies

Abstract

Acinic cell carcinoma (ACC) of the breast is extremely rare and is characterized by widespread acinar cell-like differentiation. We report of a 39-year-old woman presented with a palpable breast mass with significant morphological, immunohistochemical and ultrastructural findings. Histologically, ACC showed a diffuse glandular infiltrative pattern, with small acinar or glandular structures mixed with solid nests. Neoplastic cells were monotonous proliferation of cells with a granular or clear cytoplasm, resembling acinar cells of the salivary glands or Paneth cells. Both glandular and solid tumor cell populations were strongly positive for lysozyme and α-1-antitrypsin.

Keywords: Acinic cell carcinoma; Breast neoplasms; Electron microscopy; Immunohistochemistry.

Figure 1

The tumor was a 5.5×3.0 cm, ill defined mass, with a gray brown rubbery consistency and a slightly lobulated appearance.

Figure 2

Tumor cells growing in diffuse infiltrative patterns with small acinar or glandular structures and large solid nests in a fibro-fatty stroma and a normal mammary parenchyma (H&E stain, ×40).

Figure 3

Tumor cells were characterized by monotonous round cells with a finely granular, weakly eosinophilic, or clearly vacuolated cytoplasm and resembled acinic cells of the salivary glands (H&E stain, ×200).

Figure 4

Tumor cells showing dark eosinophilic coarse granules, resembling Paneth cells. Nuclei were irregular, and some intranuclear inclusions were noted (H&E stain, ×200).

Figure 5

Large solid nests of tumor cells revealed central comedo-like necrosis, reminiscent of ductal carcinoma in situ (H&E stain, ×100).

Figure 6

Immunohistochemical staining shows (A) strong immunoreactivity to lysozyme, (B) complete circumferential intense staining for E cadherin, (C) focal cytoplasmic reaction to S-100 protein, and (D) weak positivity for CK 7 in the luminal membrane of tumor cells and a strong positive reaction in normal ducts (A-C, ×100; D, ×200).

Figure 7

Electron microscopy revealed numerous variably sized electron dense granules in the cytoplasm, that were consistent with acinar cell granules, and a prominent, rough endoplasmic reticulum (×7,000).