MYB-NFIB gene fusion in adenoid cystic carcinoma of the breast with special focus paid to the solid variant with basaloid features.

Abstract

Adenoid cystic carcinomas (ACCs) from various anatomical sites harbor a translocation t(6;9)(q22-23;p23-24), resulting in MYB-NFIB gene fusion. This gene fusion is not well studied in mammary ACCs, and there are no studies examining this abnormality in solid variant of ACC with basaloid features (SBACC), a high-grade variant thought to behave more aggressively than ACCs with conventional histologic growth. Our aim was to investigate the frequency of MYB-NFIB gene fusion in mammary ACCs with a focus paid to SBACC. MYB rearrangement and MYB-NFIB fusion were assessed by fluorescence in situ hybridization and reverse-transcription polymerase chain reaction, respectively. Histologic features and the presence of MYB rearrangement were correlated with clinical outcome. MYB rearrangement was present in 7 (22.6%) of 31 mammary ACCs (5/15 [33.3%] ACCs with conventional growth; 2/16 [12.5%] SBACCs). One patient with conventional ACC developed distant metastasis, and no patients had axillary lymph node involvement by ACC (mean follow-up, 34 months; range, 12-84 months). Two patients with SBACC had axillary lymph node involvement at initial surgery, and 2 additional patients experienced disease recurrence (1 local, 1 distant; mean follow-up, 50 months; range, 9-192 months). MYB-NFIB fusion status did not correlate with clinical outcome in studied patients. We confirm that MYB-NFIB gene fusion is observed in mammary ACCs and that a subset lacks this abnormality. This study is the first to confirm the presence of MYB rearrangement in SBACC. Additional validation with long-term follow-up is needed to determine the relationship, if any, between MYB-NFIB gene fusion and clinical outcome.