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

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.目的： 探讨原发性肺黏液表皮样癌（pulmonary mucoepidermoid carcinoma，PMEC）中MAML2基因重排、相关融合形式及其临床病理学特征。 方法： 收集复旦大学附属中山医院和附属肿瘤医院2017—2020年确诊的原发性PMEC 46例，采用荧光原位杂交（FISH）法检测MAML2基因重排，进一步用靶向RNA高通量测序（RNAseq）法检测20例PMEC中的基因融合形式，并分析MAML2基因重排、融合形式及各临床病理学特征与预后之间的关系。 结果： 原发性PMEC患者平均发病年龄41岁（范围15~71岁）；男女比例约1.1∶1.0；组织病理学上多为低级别；临床分期以Ⅰ~Ⅱ期为主；FISH法检测MAML2基因重排，总体阳性率80.4%（37/46），在低级别PMEC中MAML2阳性率更高（91.7%，33/36）；靶向RNAseq结果显示19例FISH阳性的病例均有基因融合，以CRTC1-MAML2融合基因为主（16/19），另外3例为CRTC3-MAML2融合基因（3/19），融合形式位置均为CRTC1/3（外显子1）-MAML2（外显子2）；1例FISH阴性的患者未检测到基因融合；与MAML2 FISH阴性患者相比，携带CRTC1-MAML2融合基因的PMEC更常见于年龄≤40岁、肿瘤最大径≤2 cm、低级别和临床分期早（Ⅰ+Ⅱ期）的患者（均P<0.05）；3例携带CRTC3-MAML2融合基因的PMEC患者均为女性、临床分期早（Ⅰ+Ⅱ期）的患者。单因素分析显示MAML2基因重排/融合、发病年龄≤40岁、肿瘤体积小、组织病理学分级低、临床分期早、确诊时肿瘤无转移及手术治疗均与患者总生存期延长显著相关（P<0.05），但Cox回归分析提示以上指标均不是影响原发性PMEC生存的独立预后因子。 结论： MAML2基因重排在PMEC中发生率高提示其为重要的分子诊断指标。RNAseq检测证实CRTC1/3-MAML2是PMEC中主要基因融合形式，提示MAML2融合转录可能是PMEC发生中的重要驱动因素。MAML2基因重排/融合及相关临床病理特征与预后好密切相关。.