Objective: To investigate the feasibility of circulating tumor DNA (ctDNA) in detecting small cell lung cancer (SCLC) gene mutations and its prognostic value in chemotherapy and/or radiotherapy for SCLC patients. Methods: A total of 77 SCLC patients who were admitted to the Department of Thoracic Medical Oncology and the Department of Thoracic Radiation Oncology of Zhejiang Cancer Hospital from July 2016 to November 2019 were included. There were 66 males and 11 females, with a median age of 60 years. Among them, 42 cases were in limited stage (LS) and 35 cases were in extensive stage (ES). Next-generation sequencing (NGS) of patients' plasma ctDNA was performed before treatment. The differences of mutated genes and signaling pathways between LS and ES patients were analyzed and compared. Blood-based tumor mutation burden (bTMB) was calculated according to detected somatic cell mutations. Patients were divided into the high bTMB and the low bTMB groups according to the optimal threshold calculated by R software. Log-rank tests were used to compare progression-free survival (PFS) between the high bTMB and the low bTMB groups. Results: Among the 77 patients, 76 patients had gene mutations detected in their plasma, and the positive rate of ctDNA test was 98%. Among the 76 patients, the genes with the highest mutation frequency were TP53 (89%), RB1 (70%), LRP1B (34%), CREBBP (21%), MLL3 (21%), MLL2 (16%), NOTCH1 (13%), ROS1 (13%), BRCA2 (12%), and PTPRD (12%). The most common mutated genes in LS patients were TP53 (90%), RB1 (68%), LRP1B (24%), MLL2 (22%), and BRCA2 (17%); the most common mutated genes in ES patients were TP53 (89%), RB1 (71%), LRP1B (46%), CREBBP (31%), and MLL3 (29%). The mutation rates of NOTCH1 and CREBBP genes were significantly higher in ES patients (31.4% and 22.9%) than those in LS patients (11.9% and 4.8%) (both P<0.05). Signaling pathway analysis showed that there were more NOTCH pathway gene variations in ES patients. Among LS patients, patients in the high bTMB group (≥ 6.96 mutations/Mb) had a longer PFS than that in the low bTMB group (<6.96 mutations/Mb) (P=0.033); but no such difference was noted in ES patients. Conclusion: Plasma ctDNA sequencing detected SCLC gene mutation profiles similar to those reported in previous literature, thus ctDNA could be used as a tool to study SCLC genomics; the mutation spectra of ES-SCLC and LS-SCLC were different. bTMB has potential prognostic value in LS-SCLCs treated with chemoradiotherapy.
目的： 探讨利用循环肿瘤DNA（ctDNA）检测小细胞肺癌（SCLC）基因突变的可行性及其在SCLC患者化疗±放疗中的预后价值。 方法： 纳入2016年7月至2019年11月浙江省肿瘤医院胸部肿瘤内科及胸部肿瘤放疗科收治的共77例SCLC患者，男66例，女11例，中位发病年龄60岁，其中局限期（LS）患者42例，广泛期（ES）患者35例。对患者治疗前的血浆ctDNA进行二代测序（NGS）。分析比较LS和ES患者突变基因和信号通路的差异。根据检测到的体细胞突变，计算血浆肿瘤突变负荷（bTMB）。使用R软件计算bTMB的最优阈值并将患者分为高bTMB组和低bTMB组，使用log-rank检验比较高bTMB组和低bTMB组的无进展生存期（PFS）。 结果： 77例患者中，76例患者血浆中检测到基因突变，ctDNA检测阳性率为98%。在76例患者人群中，突变频率最高的基因分别为TP53（89%）、RB1（70%）、LRP1B（34%）、CREBBP（21%）、MLL3（21%） MLL2（16%）、NOTCH1（13%）、ROS1（13%）、BRCA2（12%）和PTPRD（12%）。LS患者最常见的突变基因为：TP53（90%）、RB1（68%）、LRP1B（24%）、MLL2（22%）和BRCA2（17%）；ES患者最常见的突变基因为：TP53（89%）、RB1（71%）、LRP1B（46%）、CREBBP（31%）和MLL3（29%）。NOTCH1和CREBBP基因的突变率在ES患者中（31.4%和22.9%）显著高于LS患者（11.9%和4.8%）（均P<0.05）。信号通路分析显示，ES患者携带更多NOTCH通路基因变异。在LS患者中，高bTMB组（≥ 6.96个突变/Mb）的患者较低bTMB组（<6.96个突变/Mb）的患者PFS更长（P=0.033）；而在ES患者中未显示出这种差异。 结论： 血浆ctDNA测序检测出与既往文献报道类似的SCLC基因突变谱，ctDNA可以作为研究SCLC基因组学的工具；ES-SCLC和LS-SCLC的基因突变频谱存在差异；bTMB在接受放化疗治疗的LS-SCLC中具有潜在的预后预测价值。.
Keywords: Blood-based tumor mutation burden; Chemoradiotherapy; Prognosis; Small cell lung cancer; ctDNA.