Lacrimal gland pleomorphic adenoma and carcinoma ex pleomorphic adenoma: genomic profiles, gene fusions, and clinical characteristics

Abstract

Purpose: To study genetic alterations in lacrimal gland pleomorphic adenoma (PA) and carcinoma ex pleomorphic adenoma (Ca-ex-PA) with focus on copy number changes and expression patterns of the translocation target genes PLAG1, HMGA2, and CRTC1-MAML2 in relation to clinical data.

Design: Experimental study.

Participants: A total of 36 tumors from 32 patients with lacrimal gland PA or Ca-ex-PA were included in the study.

Methods: Genome wide, high-resolution array-based comparative genomic hybridization (arrayCGH) and immunohistochemistry were used to study the genomic profiles and expression patterns of the translocation targets PLAG1, HMGA2, and CRTC1-MAML2.

Main outcome measures: Copy number alterations (gains/losses) and protein expression of PLAG1, HMGA2, and CRTC1-MAML2.

Results: Genome-wide arrayCGH analysis revealed normal genomic profiles in 10 of 17 PA samples. The average number of genomic imbalances per tumor was 3.25 (range, 1-7) in primary and recurrent PAs with alterations compared with 7.7 (range, 4-12) in Ca-ex-PAs. Five recurrent copy number alterations were identified in PAs, including losses of 1pter-p31.3, 6q22.1-q24.3, 8q24.22-q24.3, and 13q21.31-q21.33, and gain of 9p23-p22.3. Gain of 9p23-p22.3 also was seen in a Ca-ex-PA. In Ca-ex-PA, gain of 22q12.3-qter was the only recurrent alteration. Detailed analysis of the array data identified NFIB and PDGFB as the 2 major candidate target oncogenes that may be activated as a result of copy number gains involving 9p and 22q. Both genes have been implicated in the pathogenesis of PA and other types of salivary gland tumors. Immunohistochemical analysis revealed frequent overexpression of the translocation target gene PLAG1 in PAs and in 1 Ca-ex-PA. In contrast, overexpression of HMGA2 was observed in only a small subset of PAs. The CRTC1-MAML2 fusion oncoprotein was overexpressed in 2 mucoepidermoid Ca-ex-PAs.

Conclusions: Lacrimal and salivary gland PAs and Ca-ex-PAs have similar genomic profiles and frequently overexpress the PLAG1 oncoprotein. Copy number gains involving 9p23-p22.3 (NFIB) and 22q12-qter (PDGFB) may be of importance for disease progression in a subset of lacrimal gland PAs.