MYB and MYBL1 in adenoid cystic carcinoma: diversity in the mode of genomic rearrangement and transcripts

Abstract

MYB-NFIB and MYBL1-NFIB have been reported in ~60% of adenoid cystic carcinoma cases, but driver alterations in the remaining ~40% of adenoid cystic carcinoma remain unclear. We examined 100 adenoid cystic carcinoma cases for MYB and MYBL1 locus rearrangements by fluorescence in situ hybridization (FISH) with originally designed probe sets using formalin-fixed paraffin-embedded materials. Approximately one-third of samples were also analyzed by fusion transcript-specific RT-PCR and capture RNA sequencing. In the 27 cases with frozen materials, MYB-NFIB and MYBL1-NFIB fusion transcripts were detected in 9 (33%) and 6 cases (22%) by RT-PCR, respectively. Meanwhile, high expression of MYB (18 cases, 67%) or MYBL1 (9 cases, 33%) was detected in all 27 cases in a mutually exclusive manner, regardless of its form (full-length, truncation, or fusion transcript). Interestingly, genomic rearrangements around the corresponding highly-expressed gene were observed in all 27 cases by FISH, suggesting a causative relationship between genomic rearrangements and gene expression. Among the 100 cases, including additional 73 cases, 97 harbored genomic rearrangements in the MYB (73 cases) or MYBL1 locus (24 cases) including 10 cases with atypical FISH patterns undetectable through ordinary split FISH approaches: breakpoints far distant from MYB (5 cases) and a small NFIB locus insertion into the MYB (3 cases) or MYBL1 locus (2 cases). In clinicopathological analyses, histological grade, primary tumor size, and lymph node metastasis were identified as prognostic factors, whereas MYB/MYBL1 rearrangements were not, but were associated with histological grade. In the present study, MYB or MYBL1 locus rearrangement was detected in nearly all adenoid cystic carcinoma cases, and therefore it would be a good diagnostic marker for adenoid cystic carcinoma. However, fusion transcript-specific RT-PCR for MYB-NFIB and MYBL1-NFIB and ordinary split FISH assays for MYB and MYBL1 were less sensitive, and thus detection methods should be judiciously designed because of the diversity of rearrangement modes in adenoid cystic carcinoma.

Clinically Integrated Molecular Diagnostics in Adenoid Cystic Carcinoma

“…4A–C). In other words, relying on a single method may be inferior because our findings underscore the complementary nature of various testing modalities .…”

“…2A), possibly reflecting intratumoral heterogeneity [41] with respect to the underlying MYB-NFIB and NOTCH1 gene alterations. Unless limited by tissue availability, In other words, relying on a single method may be inferior because our findings underscore the complementary nature of various testing modalities [38].…”

“…Fusions for MYB‐NFIB or MYBL1‐NFIB (40%) and NOTCH1 mutations (25%) were the most common alterations. Across all cancer types tested in our institution (n = 2,701 cases were genotyped between 2013 and 2018) , we have only seen MYB and MYBL1 fusions in adenoid cystic carcinomas (specificity: 100%) . We modeled that even if a non‐ACC would harbor one MYB/MYBL1 fusion, it would take ∼14 cases of non‐ACC for the specificity to drop below 99.5%.…”

“…genotyped between 2013 and 2018) [27,37], we have only seen MYB and MYBL1 fusions in adenoid cystic carcinomas (specificity: 100%) [38]. We modeled that even if a non-ACC would harbor one MYB/MYBL1 fusion, it would take 14 cases of non-ACC for the specificity to drop below 99.5%.…”

MYB rearrangement and immunohistochemical expression in adenomyoepithelioma of the breast: a comparison with adenoid cystic carcinoma

“…Our results are in line with this study and support the use of MYB IHC as a useful adjunct to establishing the diagnosis of adenoid cystic carcinoma in the breast as well as non‐breast sites. Recent genetic investigations demonstrate that alternative mechanisms for MYB pathway activation including MYB amplification or rearrangement of MYBL1 (a closely related gene with similar function) may be present in a considerable number of ACC cases that lack the classic MYB–NFIB translocation . These provide a logical potential explanation for the observations that MYB expression by immunohistochemistry may be more sensitive for ACC of the breast compared to FISH.…”