This study is a prospective, single-center, open-label, single-arm clinical trial to assess the safety and efficacy of umbilical cord blood in cancer treatment-induced thrombocytopenia (CTIT) patients. It plans to recruit subjects aged 12 to 65 years old with CTIT. The study involves intravenous infusion of umbilical cord blood, with platelet transfusion as supportive therapy if necessary. The trial consists of three phases: screening (baseline assessments and enrollment), treatment (umbilical cord blood infusion), and follow-up (blood routine tests at Days 3, 7, 14, and 28 post-treatment to record platelet counts, first response time, maximum and minimum values, and calculate efficacy rates while observing changes in thrombocytopenia grading). A total of 25 subjects will be enrolled, and they will undergo evaluation for safety and efficacy based on treatment-related adverse events, GVHD incidence, and hematological improvements.

Umbilical cord blood infusion involves cord blood-derived hematopoietic stem cells sourced from the Umbilical Cord Blood Hematopoietic Stem Cell Bank, with HLA typing 0-3/10 matched, total nucleated cells (TNC) >1×10^7/kg, and ABO blood type identical to the recipient. Following intravenous infusion, it promotes platelet recovery by providing hematopoietic stem cells, mesenchymal stem cells, endothelial progenitor cells, and growth factors that stimulate bone marrow progenitor cell proliferation in the in vivo environment, thereby elevating platelet levels.

The primary endpoint of this study is:

Treatment efficacy rate: Post-treatment platelet count ≥100×10^9/L, or an increase of ≥50×10^9/L from baseline, or an increase of ≥100% from baseline.

Secondary endpoints include:

Platelet first response time: Time to first platelet count ≥100×10^9/L without platelet transfusion; Maximum and minimum platelet counts; Incidence of bleeding events after initial infusion; Number of platelet transfusions; Changes in thrombocytopenia grading; Treatment-related adverse events; Incidence and grading of graft-versus-host disease (GVHD).

Inclusion Criteria:

1. Aged 12 to 65 years at the time of signing the informed consent, regardless of gender.
2. Meets the diagnostic criteria for cancer treatment-induced thrombocytopenia (CTIT):Peripheral blood platelet count < 100 × 10⁹/L; Prior definite exposure to a chemotherapy agent (or tumor-targeted therapy, immunotherapy, or other anti-tumor drugs) known to cause thrombocytopenia, with gradual improvement of thrombocytopenia-related symptoms/signs or normalization of platelet count after discontinuation of the offending drug; Presence or absence of bleeding tendency, such as petechiae, purpura, unexplained epistaxis, or even severe organ/tissue hemorrhage;
3. No significant hepatic or renal impairment: ALT and AST ≤ 2.5 × upper limit of normal (ULN), serum creatinine (Cr) and blood urea nitrogen (BUN) ≤ 1.25 × ULN;
4. Karnofsky Performance Status (KPS) score ≥ 60 (see Appendix 1), Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2 (see Appendix 2);
5. Estimated life expectancy of more than 3 months.

Exclusion Criteria:

1. Other causes of thrombocytopenia, in particular exclusion of underlying diseases or comorbidities such as aplastic anemia, acute leukemia, radiation sickness, immune thrombocytopenia (ITP), hypersplenism, or bone marrow infiltration by tumor cells;
2. Use of non-anti-tumor medications known to cause thrombocytopenia (including but not limited to sulfonamides and other drugs);
3. Pseudothrombocytopenia induced by ethylenediaminetetraacetic acid (EDTA) anticoagulant;
4. Uncontrolled malignant tumor, hypertension, or diabetes mellitus;
5. Active infection, including but not limited to known HIV positivity, active hepatitis B or C, or syphilis;
6. Poor compliance;
7. Known allergy or hypersensitivity to any component of the study intervention (umbilical cord blood or related products);
8. Participation in another clinical trial within 1 month prior to enrollment or current participation in another clinical trial;
9. Any other condition that, in the investigator's judgment, makes the patient unsuitable for participation in this clinical study.