Rearrangements, Expression, and Clinical Significance of MYB and MYBL1 in Adenoid Cystic Carcinoma: A Multi-Institutional Study

Abstract

Adenoid cystic carcinoma (ACC) is an aggressive head and neck malignancy characterized by a t (6;9) translocation resulting in an MYB-NFIB gene fusion or, more rarely, an MYBL1 fusion. The true frequency and clinical significance of these alterations are still unclear. Here, we have used tissue microarrays and analyzed 391 ACCs and 647 non-ACC salivary neoplasms to study the prevalence, expression, and clinical significance of MYB/MYBL1 alterations by FISH and immunohistochemistry. Alterations of MYB or MYBL1 were found in 78% of the cases, of which 62% had MYB alterations and 16% had MYBL1 rearrangements. Overexpression of MYB/MYBL1 oncoproteins was detected in 93% of the cases. MYB split signal, seen in 39% of the cases, was specific for ACC and not encountered in non-ACC salivary tumors. Loss of the 3'-part of MYB was enriched in grade 3 tumors and was a significant independent prognostic biomarker for overall survival in multivariate analyses. We hypothesize that loss of the 3'-part of MYB results from an unbalanced t(6;9) leading to an MYB-NFIB fusion with concomitant loss of the segment distal to the MYB breakpoint in 6q23.3. Our study provides new knowledge about the prevalence and clinical significance of MYB/MYBL1 alterations and indicates the presence of genes with tumor suppressive functions in 6q23.3-qter that contribute to poor prognosis and short overall survival in ACC.

Keywords: FISH; MYB; MYBL1; adenoid cystic carcinoma; immunohistochemistry; prognostic biomarker; tumor suppressor gene.

Figure 1

FISH analyses of MYB and MYBL1 in ACC. (A) ACC with a split MYB signal (separated red and green signals indicated by arrowheads). (B) ACC with loss of the 3′-part of MYB (loss of one red signal; arrowheads indicate the remaining green signal). (C) ACC with gain of one copy of MYB (three fused red/green signals indicated by arrowheads). (D) ACC with a split MYBL1 signal (separated red and green signals indicated by arrowheads). Images were captured using an 100× objective.

Figure 2

MYB and MYBL1 alterations in ACC. Pie charts showing the frequencies of different types of MYB and MYBL1 alterations detected by FISH in ACC.

Figure 3

IHC staining of the MYB and MYBL1 oncoproteins in ACC tissue microarrays. (A–C) MYB staining in three ACCs with MYB split signals. (D–F) MYB staining in three ACCs with loss of the 3′-part of MYB. (G) MYB staining in an ACC with gain of one copy of MYB. (H,I) MYBL1 staining in two ACCs with MYBL1 split signals (no MYB rearrangements by FISH). (J–L) MYB/MYBL1 staining in three ACCs with no rearrangements of MYB or MYBL1 by FISH. Images were captured using a 20× objective.

Figure 4

Prognostic significance of MYB and MYBL1 alterations in ACC. (A) OS in ACC patients with or without MYB rearrangements. (B) OS in ACC patients with or without MYBL1 rearrangements. (C) OS of ACC patients with or without MYB split signal. (D) OS of ACC patients with or without loss of the 3′-part of MYB. (E) Distribution of ACC cases with or without loss of the 3′-part of MYB by tumor grade. (F) Distribution of ACC cases with or without loss of the 3′-part of MYB by median age.