Clinicopathological, immunohistochemical and molecular features of acinic cell carcinoma of the breast

Abstract

Breast acinic cell carcinoma (ACC) is a rare subtype of breast cancer. Accurate diagnosis of ACC using core needle biopsy (CNB) is pivotal for the use of effective treatments and patient prognosis. In the present study, a detailed analysis of the morphological, immunohistochemical and gene mutation features of 2 cases of ACC was performed. CNB was performed prior to surgical excision. The breast ACC in the present cases exhibited overt burrowing labyrinthine networks or 'hand-holding-hand' features. The tumor cells in both of the present cases expressed cytokeratin (CK)7, S100 and CK5/6, but were negative for p63, estrogen receptor and progesterone receptor. GATA binding protein 3 was positive in case 1 but negative in case 2. Fluorescence in situ hybridization indicated no ETS variant transcription factor 6 break-apart probe detection. Next-generation sequencing results revealed the same mutation and a similar abundance in exon 27 (NM_005120.2; c.3817G>T; p.A1273S) of the mediator of RNA polymerase II transcription, subunit 12 homolog (MED12) gene in both patients. To conclude, the findings of the present study suggested that recognition of this rare 'hand-holding-hand' structure could potentially be beneficial for avoiding patient misdiagnosis. In addition, it could be suggested that a mutation in the MED12 exon 27 was associated with the formation of a burrowing labyrinthine network or 'hand-holding-hand' feature.

Keywords: acinic cell carcinoma; breast cancer; mediator of RNA polymerase II transcription; subunit 12 homolog.

Figure 1.

Characteristics of the breast acinic cell carcinoma observed on ultrasound scans. (A) Blood flow signal in the mass showed high resistance waveform in case 1. (B) The tumor tissue exhibited an irregular shape with clear boundaries and a strong dotted echo and blood flow signal could be observed in the mass in case 2. TIB, thermal index bone; MI, mechanical index; fps, frames per second; Col404, color 404.

Figure 2.

Macroscopic features of the tumor. (A) Tumor boundary was not well defined with a gray-white cut surface in case 1. (B) Following sectioning, the tumor was gray-white with a rubbery consistency and clear boundary (red box) in case 2.

Figure 3.

Staining results of the tumor tissue from case 1. Imaging of the tumor tissue demonstrated (A) invasive carcinoma (magnification, ×18), (B) the ‘hand-holding-hand’ pattern of tumor cells (red box; magnification, ×66), (C) the fibrotic focus (red box; magnification, ×10), (D) the ‘hand-holding-hand’ pattern (red box; magnification, ×50), (E) the ‘hand-holding-hand’ pattern (red box; magnification, ×50) in another area, (F) cell characteristics of obvious atypia and mitotic figures (insert; magnification, ×240), (G) positive S100 staining highlighting the ‘hand-holding-hand’ pattern (magnification, ×78) and (H) human epidermal growth factor receptor-2 immunohistochemistry staining scored as 2+ (magnification, ×150).

Figure 4.

Staining results of the tumor tissue from case 2. Imaging of the tumor tissue demonstrated (A) invasive carcinoma (magnification, ×20), (B) the ‘hand-holding-hand’ pattern of tumor cells (red box; magnification, ×120), (C) the clear boundary of the tumor (magnification, ×010), (D) the ‘hand-holding-hand’ pattern (red box; magnification, ×35), (E) the ‘hand-holding-hand’ pattern (red box; magnification, ×35) in another area, (F) cell characteristics of obvious atypia and mitotic figures (insert; magnification, ×260), (G) positive S100 staining and the ‘hand-holding-hand’ pattern (magnification, ×78) and (H) human epidermal growth factor receptor-2 immunohistochemistry staining scored as 2+ (magnification, ×150).