[MAML2 gene rearrangement, fusion patterns and clinicopathological characteristics in primary pulmonary mucoepidermoid carcinoma].

ABSTRACT

Objective: To investigate MAML2 gene rearrangement, gene fusion patterns, and the clinicopathological characteristics of primary pulmonary mucoepidermoid carcinoma (PMEC). Methods: Forty-six cases of primary PMEC from Fudan University Zhongshan Hospital and Fudan University Shanghai Cancer Center between 2017 and 2020 were collected. MAML2 gene rearrangement in all cases was detected by fluorescence in situ hybridization (FISH). In 20 cases, MAML2 fusion patterns were detected by targeted RNA sequencing (RNAseq). The relationship between MAML2 gene rearrangement, fusion patterns, clinicopathological characteristics, and prognosis was analyzed. Results: The average age of PMEC patients was 41 years (range 15-71 years); the ratio of male to female was about 1.1 ∶ 1.0. Most PMECs were low grade in histopathology with an early clinical stage (stageⅠ-Ⅱ).The overall positive rate of MAML2 gene rearrangement detected by FISH was about 80.4% (37/46), and the rate was higher in low-grade PMEC (91.7%, 33/36). Of the 20 cases detected by RNAseq, all the 19 FISH positive cases showed gene fusion, mainly CRTC1-MAML2 fusion (16/19), the other three cases showed CRTC3-MAML2 fusion (3/19), the break point of all the fusion patterns was CRTC1/3 (exon 1)-MAML2 (exon 2); No gene fusion was detected in the single FISH negative case; Compared with the MAML2 FISH negative patients, the PMECs carrying CRTC1-MAML2 fusion were more commonly found in patients age ≤ 40 years, maximum tumor diameter ≤ 2 cm, low histopathological grade and early clinical stage (all P<0.05); The three PMECs carrying CRTC3-MAML2 fusion gene were all female with early clinical stage; Univariate analysis showed that MAML2 gene rearrangement/fusion, onset age ≤ 40 years old, smaller tumor size, low histopathological grade, early clinical stage, no metastasis at diagnosis and surgical treatment were significantly correlated with overall survival (P<0.05), but Cox regression analysis suggested that none of the above indicators were the independent prognostic factors for the survival of PMEC. Conclusions: The high incidence of MAML2 gene rearrangement in PMEC suggests that it is an important molecular diagnostic marker of PMEC. RNAseq confirms that CRTC1/3-MAML2 is the main fusion pattern in PMEC, suggesting that MAML2 fusion transcription may be an important driving factor of PMEC. MAML2 rearrangement/fusion and related clinicopathological characteristics are associated with good prognosis.