Abstract CT219: Efficacy and safety of Low dose radiotherapy (LDRT) concurrent Atezolizumab (Atezo) plus chemotherapy as first line (1L) therapy for ES-SCLC: Primary analysis of Phase II MATCH study

Abstract Background: The IMpower133 represented the current standard of care in the 1L setting for patients (pts) with ES-SCLC (extensive-stage small cell lung cancer). However, there are still unmet needs for ES-SCLC treatment. LDRT could play a key role in the priming effect of immune system by acting as an immune adjuvant and having sensitive cytotoxic activity to SCLC. The interim analysis of MATCH study after stage I showed promising benefit and tolerability of combination of Atezo + chemotherapy + LDRT in pts with ES-SCLC. Here we report the primary efficacy and safety results of this study. Methods: The MATCH study was a single-arm phase II trial conducted in 8 centers across China. Previously untreated ES-SCLC pts with measureable disease per RECIST v1.1 at baseline, age≥18, ECOG 0-1 were eligible. Atezo (1200 mg IV, D1) + Cisplatin (75 mg/m2 IV, D1)/Carboplatin (AUC = 5 IV, D1) +Etoposide (100 mg/m2 IV, D1-D3) were administrated on a 21-day cycle for four cycles. Concurrent LDRT (15 Gy/5f) were conducted from D1-D5 in the first cycle. Then pts received Atezo maintenance until loss of clinical benefit or unacceptable toxicity. The primary endpoint was objective response rate (ORR), defined as the proportion of patients with a complete response or partial response on two consecutive occasions ≥ 4 weeks apart, as determined by the investigator according to RECIST v1.1. The secondary endpoints included disease control rate (DCR), progression-free survival (PFS), overall survival (OS) and safety. A Simon’s minimax 2-stage design was adopted. Results: As the cutoff date of 30th Nov. 2022, 56 pts have been enrolled. 49 (87.5%) were males; mean age was 58.9 years with 78.6% pts had ECOG PS of 1. 80.4% pts had smoking history. Most pts were staged T4 (n = 33, 58.9%), N3 (n = 37, 66.1%) and M1(n = 40, 71.4%). Median follow-up was 14.8 months (range: 11.6-17.8 m). The confirmed ORR was 87.5% (95% CI: 75.9%-94.8%), all partial response. DCR was 94.6% (95% CI: 85.1%-98.9%). Median PFS was 6.9 m (95% CI: 5.4-9.3 m). The 6-month and 12-month PFS rate were 56.5% and 27.7%. Median OS was not reached (NR, 95% CI: 13.3m, NR). The 12-month OS rate was 71.9%. The safety profile, analyzed in all 56 pts, was consistent with the previous reports. Neutrophil count decreased (60.7%), white blood cell count decreased (58.9%) and platelet count decreased (23.2%) were the most common grade (G) 3-4 adverse events (AE). G5 AE occurred in 1 pt (pneumonia and pulmonary embolism). 4 pts experienced AEs leading to treatment discontinuation. IrAEs were reported in 21 (37.5%) pts, most common irAEs were hyperthyroidism (5.4%) and rash (5.4%). Radiation pneumonitis (G1) was observed in 1 pt. Conclusions: Adding LDRT to Atezo + chemotherapy shows impressive antitumor activity, potential survival benefit and well tolerability in 1L treatment of ES-SCLC. Clinical registration: NCT04622228. Citation Format: Lin Zhou, Jianguo Sun, Conghua Xie, Youling Gong, Meijuan Huang, Zhiyong Yuan, Lin Wu, Hui Wang, Nan Bi, Yaping Xu, Jiang Zhu, Yongmei Liu, Yan Zhang, Min Fan, Bingwen Zou, Min Yu, Yanying Li, Feifei Na, Weigang Xiu, Yong Xu, Jin Wang, Xuanwei Zhang, Jianxin Xue, You Lu. Efficacy and safety of Low dose radiotherapy (LDRT) concurrent Atezolizumab (Atezo) plus chemotherapy as first line (1L) therapy for ES-SCLC: Primary analysis of Phase II MATCH study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT219.