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

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.