The incidence of synchronous bilateral breast carcinomas (BBCs) has increased with a more frequent use of magnetic resonance imaging screening of the contralateral breast in women with newly diagnosed breast cancer. A total of 30% of all BBCs occur synchronously. In the present study, we describe a unique case of synchronous BBC in a 59-year-old previously healthy woman with no known family history of breast or ovarian cancer. At the time of diagnosis the patient had an invasive lobular carcinoma (ILC) in the right breast and an adenoid cystic carcinoma (ACC) in the left breast. To the best of our knowledge, this is the first published case of bilateral, simultaneously occurring ACC and ILC of the breast. Genome-wide genomic profiling of the tumors revealed that they had distinctly different genomic imbalances. The ACC had a 5.7 Mb interstitial 6q deletion with a breakpoint located in the 3'-part of MYB, resulting in loss of the last coding exon of MYB and its 3'-UTR. RT-PCR analysis confirmed that the tumor expressed an ACC-specific MYB-NFIB fusion transcript. In contrast, the ILC had no rearrangements of 6q or MYB-NFIB gene fusion but showed instead gain of 1q21.1-qter, loss of 16q11.2-qter, and 22q12.2-q12.3 as the sole genomic imbalances. Notably, concurrent gains of 1q and losses of 16q are characteristic features of ILC. Collectively, our findings indicate that the ACC and ILC had originated independently of each other and that the MYB-NFIB fusion is a specific biomarker for breast ACC.
Keywords: MYB; adenoid cystic carcinoma; breast cancer; genomic profiling; invasive lobular carcinoma; synchronous bilateral breast carcinoma.