A Phase Ib/II Clinical Study Evaluating the Safety and Efficacy of Tislelizumab in Combination With Golidocitinib and Selinexor for the Treatment of R/R NKTCL

Inclusion Criteria: * Voluntarily participate in the clinical study; fully understand and provide informed consent (via a signed Informed Consent Form, ICF); willing and able to comply with all trial procedures. * Histopathologically confirmed diagnosis of extranodal NK/T-cell lymphoma, nasal type (NKTCL) by the participating study center. * Relapsed or refractory NKTCL after failure of asparaginase-based chemotherapy ± radiotherapy: * Relapse: Disease recurrence \>6 months after achieving complete response (CR) to prior therapy. * Refractory: Failure to achieve CR or disease progression after adequate systemic therapy (≥4 cycles of a combination regimen). * For Phase II: Patients must have received prior anti-PD-1 monoclonal antibody therapy and remain refractory. * At least one measurable or evaluable lesion per Lugano 2014 criteria: * Measurable lesion: CT/MRI: Longest diameter ≥1.5 cm (lymph nodes) or ≥1.0 cm (extranodal lesions).Post-radiation lesions require radiological evidence of progression. * Evaluable lesion: FDG-PET: Lymph node/extranodal lesion with uptake \> liver and imaging consistent with lymphoma. * Age ≥18 years at the time of ICF signing. * Life expectancy \>12 weeks. * ECOG performance status 0-2. * Adequate organ and bone marrow function: * Hematology (no transfusion/G-CSF support within 14 days): ANC ≥1.5×10⁹/L (≥0.5×10⁹/L if bone marrow involvement)；Platelets ≥100×10⁹/L (≥50×10⁹/L if bone marrow involvement)；Hemoglobin ≥8.0 g/dL. * Liver function: Total bilirubin ≤1.5×ULN (≤3.0×ULN for Gilbert's syndrome or liver involvement). ALT/AST ≤2.5×ULN (≤5.0×ULN with liver involvement). * Renal function: Serum creatinine ≤1.5×ULN OR creatinine clearance (Cockcroft-Gault) ≥50 mL/min. * Coagulation: INR ≤1.5×ULN; PT/APTT ≤1.5×ULN (unless on anticoagulants within therapeutic range). * Cardiac function: LVEF ≥50% by echocardiography (ECHO). * Recovery from prior anticancer therapy toxicities to CTCAE v5.0 Grade ≤1 or baseline. Exceptions: Irreversible Grade 2 toxicities unlikely to worsen during the study (e.g., neuropathy, alopecia) per investigator's assessment. * For women of childbearing potential (WOCBP): Negative serum pregnancy test within 7 days before enrollment. WOCBP and male participants with WOCBP partners must agree to use effective contraception from ICF signing until ≥6 months after the last study dose. Exclusion Criteria: * History of malignancy within the past 5 years, with the exception of: Locally curable malignancies treated with curative intent (e.g., basal or squamous cell skin cancer, thyroid carcinoma, superficial bladder cancer, or in situ carcinoma of the prostate, cervix, or breast). * Any of the following prior treatments: * History of allogeneic hematopoietic stem cell transplantation (allo-HSCT) within 5 years prior to the first dose (patients with allo-HSCT \>5 years before the first dose and no active graft-versus-host disease may enroll). * Autologous hematopoietic stem cell transplantation (auto-HSCT) within 3 months prior to the first dose. * Prior use of JAK inhibitors, STAT3 inhibitors, or XPO1 inhibitors. * Current use of vitamin K antagonists, antiplatelet agents, or anticoagulants (or inability to discontinue within 1 week before the first dose). * Systemic glucocorticoids or immunosuppressants within 14 days prior to enrollment (allowed: topical, ocular, intra-articular, intranasal, or inhaled glucocorticoids; short-term \[≤7 days\] prophylactic use for non-autoimmune conditions). * Cytotoxic chemotherapy within 14 days prior to enrollment. * Systemic anticancer therapy (including monoclonal antibodies or immunotherapy) within 4 weeks prior to the first dose. * Major organ surgery within 6 weeks or radiotherapy within 90 days prior to enrollment. * Radioimmunoconjugate therapy within 10 weeks prior to enrollment. * Use of other investigational drugs requiring investigator's risk-benefit assessment. * Participation in other clinical trials with investigational drugs within 30 days prior to enrollment. * Vaccines (except influenza vaccines) within 28 days prior to enrollment. * Active infections, including: * Active or latent tuberculosis (positive tuberculin skin test \[PPD\] with induration ≥10 mm or radiologically confirmed active lesions). * Known HIV infection or AIDS. * Chronic active hepatitis B or C: HBV: Exclude if HBV DNA detectable (↑center-specific ULN). HCV: Exclude if HCV RNA detectable (↑center-specific ULN). * Other active viral infections (e.g., herpes zoster, CMV) requiring treatment. Infections requiring intravenous antimicrobial therapy. * Uncontrolled cardiac conditions, including: * NYHA Class \>II heart failure. * Unstable angina. * Myocardial infarction within 1 year. * Clinically significant arrhythmias requiring intervention. * Persistent drug-related toxicities \>CTCAE Grade 1 (excluding alopecia) at baseline. * Uncontrolled nausea/vomiting, chronic gastrointestinal diseases, dysphagia, or prior bowel resection affecting drug absorption. * Pregnancy, lactation, or refusal to use contraception by participants of reproductive potential. * Psychiatric disorders or inability to provide informed consent. * Other conditions deemed unsuitable for study participation by the investigator.