SCLC is easy to relapse and drug resistance soon after initial treatment , although radiotherapy and chemotherapy is sensitive at first treatment. Topotecan monotherapy is recommended in the NCCN guidelines for second-line standard treatment and the CSCO SCLC guidelines for diagnosis and treatment 2020 edition, but its effective rate is low, 24% for platinum-sensitive relapse, 2-6% for platinum-resistant, overall PFS is about 3-4 months and OS is about 6-8 months. Although immunotherapy have been successful at the first-line and third-line treatments of SCLC in the extensive stage , the second-line treatment has not achieved a breakthrough, and the effective rate of third-line immune single drug is between 10-20%.It is an important challenge and breakthrough to effectively improve the efficacy and survival of second-line treatment of SCLC. Immunocombination therapy is an important strategy to improve the efficacy. Some studies have shown that PARP inhibitors and low-dose radiotherapy can improve the efficacy of immunotherapy. PARP inhibitors are not only sensitizers of chemoradiotherapy, but also immunomodulators. High dose radiotherapy has the effect of in situ vaccine and increases tumor antigen release presentation. Low dose radiotherapy promotes the penetration of immune cells into tumor stroma and tumor bed and increases immune response. The combination of high and low dose radiotherapy and immunization can improve the immune effect and increase the incidence of distant effect. So the objective of this study is to observe the efficacy and safety of second-line treatment of SCLC with SBRT and low-dose radiotherapy combined with PARP inhibitor + temozolomide and PD-1 /PD-L1 inhibitor.
SCLC patients after initial treatment failure are treated with SBRT and low-dose radiotherapy concurrent with PARP inhibitors + temozolomide +PD-1/PD-L1 inhibitors for two cycles at least, then PARP inhibitors+temozolomide+PD-1/PD-L1 inhibitors two cycles, PD-1/PD-L1 inhibitors maintenance therapy lasted for up to 2 years.