Tislelizumab in Combination with Chemotherapy ± Radiotherapy for Extensive-Stage Oligometastatic Small Cell Lung Cancer.

Inclusion criteria

• Patients must be ≥ 18 years old;
• Signed written informed consent;
• Histologically or cytologically confirmed oligometastatic extensive-stage small cell lung cancer (oligometastasis is defined as the number of distant metastatic organs≤ 3, and the number of metastases ≤ 5; The ninth edition of the AJCC/UICC/IASLC TNM Staging Criteria for Lung Cancer (Annex 1), extensive-stage SCLC for any T stage, any N stage, M1a/b/c or T3-4 cannot be included in a tolerable radiotherapy program due to multiple nodules in the lungs or excessive tumor size);
• chemotherapy must include a combination of cisplatin and etoposide;
• Expected survival≥ 12 weeks;
• ECOG score of 0 or 1 (Annex 2);
• Weight> 40 kg;
• At least 1 lesion (no prior radiotherapy) according to RECIST 1.1 guidelines, with a maximum diameter of ≥10 mm as accurately measured by computed tomography (CT) or magnetic resonance imaging (MRI) at baseline (except for lymph nodes, which must be ≥15 mm in their short axis); And the lesion is suitable for repeated and accurate measurement.
• Have not received anti-tumor therapy in the past;
• Have adequate organ and bone marrow function,
• Echocardiography: Left ventricular ejection fraction (LVEF) ≥ low limit of normal (50%)
• Evidence of postmenopausal status in female patients, or negative urine or serum pregnancy test results in premenopausal female patients. A woman is considered menopausal when she stops menstruation for 12 months without an other medical cause.
• Within 2 weeks (±1 week) prior to enrollment, the following examinations required for staging must be completed: 1) MRI of the head, CT scan of the chest and upper abdomen, ultrasound of superficial lymph nodes and whole-body ECT; Whole-body PET/CT scan is done if necessary.
• Patients with asymptomatic or stable brain metastases after treatment are allowed to enroll, and patients are required to do not need glucocorticoid therapy or discontinue glucocorticoids within 3 days before the first study dose.

Exclusion criteria

• Personnel involved in the design and/or conduct of this study.
• Previous receipt of investigational drug in this study.
• Concurrent enrollment in another clinical study, unless it is an observational (non-interventional) clinical study or the follow-up phase of an interventional study.
• There are medical contraindications to etoposide-platinum-based chemotherapy.
• History of thoracic radiotherapy prior to systemic therapy.
• Concomitant administration of any chemotherapy, biologics, or hormonal therapy for cancer treatment. Hormone therapy for noncancer-related conditions, such as hormone replacement therapy, is acceptable.
• Major surgical procedure (as defined by the investigator) within 28 days prior to the first dose.
• History of allogeneic organ transplantation.
• Patients who have been cured of aplastic anemia or other blood diseases and patients who have undergone stem cell transplantation.
• Have an autoimmune paraneoplastic syndrome (PNS) that requires systemic therapy (systemic steroids or immunosuppressants) or have clinical symptoms suggestive of an exacerbation of PNS.
• Active or previously documented autoimmune or inflammatory disease (including inflammatory bowel disease [e.g., colitis or Crohn's disease], diverticulitis [except diverticular disease], systemic lupus erythematosus, Sarcoidosis syndrome, nephrotic syndrome or nephritis, Wegener syndrome [granulomatous vasculitis, Graves' disease, rheumatoid arthritis, hypophysitis and uveitis, etc.]). The following exceptions are made to this criterion: patients with vitiligo or alopecia; Patients with hypothyroidism (e.g., after Hashimoto syndrome) who are stable after receiving hormone replacement therapy; Any chronic skin condition that does not require systemic therapy; Patients with no active disease in the past 3 years may be included in the study after discussion with the study physician; Patients with celiac disease who can be controlled by diet alone.
• Uncontrolled intercurrent illness including, but not limited to: persistent or active infection, interstitial lung disease, symptomatic congestive heart failure, uncontrolled hypertension, unstable angina, cardiac arrhythmia, severe chronic gastrointestinal disease with diarrhea, or psychiatric/social problems that may limit compliance with study requirements, recent (within 3 months) new cerebral infarction/intracerebral hemorrhage, psychiatric/social problem conditions that result in a significantly increased risk of AEs, or affect the subject's ability to provide written informed consent.
• History of another primary malignancy, with the following exceptions: malignancy treated with curative intent, no known active disease for 5 years ≥ prior to the first dose and a low risk of potential recurrence; adequately treated non-melanoma skin cancer or lentigo maligna nevus with no evidence of disease; Carcinoma in situ that has been adequately treated and has no evidence of disease.
• History of leptomeningeal carcinoma.
• History of active primary immunodeficiency.
• Active infection, including tuberculosis (clinical evaluation, including clinical history, physical examination, imaging findings, and TB examination consistent with local clinical practice), hepatitis B (known to be HBV surface antigen [HbsAg] positive), hepatitis C, or human immunodeficiency virus (HIV1/2 antibody positive). Patients with prior HBV infection or who have been cured (defined as the presence of hepatitis B core IgG antibodies and the absence of HBsAg) are eligible. Patients who are positive for hepatitis C virus (HCV) antibodies are eligible only if they are negative for HCV RNA polymerase chain reaction.
• Female patients who are pregnant or lactating.
• Those who are considered inappropriate by the investigator to participate in this study.