Romiplostim N01 Plus ATRA for Persistent Isolated Chemotherapy-Induced Thrombocytopenia After Complete Remission of Gastrointestinal Solid Tumors

Inclusion Criteria:

1. Age 18 years or older.
2. Prior diagnosis of a gastrointestinal/digestive system solid tumor, including but not limited to gastrointestinal tract, pancreatic, or colorectal cancer.
3. Complete remission of the underlying tumor after chemotherapy or antitumor treatment, with tumor-related treatment discontinued for at least 12 weeks before enrollment, no evidence of recurrence or progression by specialist assessment, and no current need for additional tumor-directed therapy.
4. Persistent isolated chemotherapy-induced thrombocytopenia, defined as platelet count \<30 x 10\^9/L on two peripheral blood tests at least 7 days apart; or platelet count slightly higher than 30 x 10\^9/L with dependence on platelet transfusion to maintain a safe platelet level.
5. Thrombocytopenia has persisted since the last chemotherapy treatment without a clear trend of spontaneous recovery.
6. Red blood cell count and neutrophil count are generally preserved, without clinically significant anemia or neutropenia.
7. Bone marrow assessment performed within 1 year after tumor diagnosis and chemotherapy shows no tumor cell infiltration; megakaryocyte count is normal or increased, with or without maturation impairment.
8. No hepatosplenomegaly, portal hypertension, or other evidence suggesting abnormal platelet redistribution as the main cause of thrombocytopenia.
9. Prior treatment with at least one thrombopoietin receptor agonist or recombinant human thrombopoietin for PICIT without response, defined as failure of platelet count to rise to a safe level or to at least 2 times baseline after at least 2 weeks of standard-dose treatment.
10. No prior use of Romiplostim N01.
11. Other platelet-raising medications have been discontinued before enrollment. No washout period is required for prior thrombopoietin receptor agonists; other investigational drugs or off-label treatments must be discontinued for at least 1 month before enrollment.
12. Ability to understand and sign the informed consent form and willingness to comply with study visits and procedures.
13. Women of childbearing potential must have a negative pregnancy test before enrollment and agree to use effective contraception during study treatment.

Exclusion Criteria:

1. Other hematologic diseases that may affect hematopoiesis or cause thrombocytopenia, including but not limited to aplastic anemia, myelodysplastic syndrome, leukemia or other hematologic malignancies, or a clear history of primary immune thrombocytopenia.
2. Active recurrence or progression of the underlying tumor, or evidence of bone marrow metastasis or tumor cell infiltration on bone marrow examination.
3. Uncontrolled chronic viral infection, including hepatitis B, hepatitis C, or HIV infection, or active severe infection at screening or within 4 weeks before screening.
4. Severe cardiac, hepatic, renal, or other organ dysfunction, or any serious organic disease that would make the participant unable to tolerate study treatment.
5. Pregnancy or breastfeeding.
6. Known severe hypersensitivity to Romiplostim, Romiplostim N01, ATRA, or any component of the study drugs.
7. Prior Romiplostim treatment associated with severe adverse reactions or lack of efficacy.
8. Poor compliance, inability to complete treatment or follow-up, psychiatric or psychological condition that prevents understanding of the study procedures, or any other condition that, in the investigator's judgment, may increase study risk or interfere with interpretation of study results.