Inclusion Criteria:
* Written informed consent prior to performing any protocol-related procedures, including screening evaluations.
* Adult aged 18 years or above.
* Metastatic or non-metastatic gastrointestinal cancer (gastric, pancreatic, colorectal…) histologically proven.
* Splenomegaly validated by Splenic volume greater than or equal to 275 mL on imaging associated with thrombocytopenia (3D volumetry)
* Ongoing thrombocytopenia with serum platelet count ≤ 80.000 mm³ observed on 2 consecutive biological assessments performed at least 7 days apart and at the latest 1 month apart. The second biological assessments should be dated at the latest 3 days from enrolment.
* Eastern Cooperative Oncology Group (ECOG) 0-2
* Life expectancy of greater than 6 months
* Adequate organ function as defined by the following:
1. Absolute neutrophil count ≥ 1000/mm³
2. Hemoglobin ≥ 8.0 g/dL
3. Creatinine \< 1.5 × ULN or creatinine clearance ≥ 40mL/min (Cockcroft-Gault formula)
4. ALAT and ASAT ≤ 5 × ULN
5. Prothrombin Rate (PR) \> 50 % (non-correctable\*) and Activated Partial Thromboplastin time (APTT) \< 1,5 second (non-correctable \*) \* non-correctable coagulopathy is defined as persistent coagulation abnormalities that cannot be corrected, even with appropriate therapeutic interventions (e.g., coagulation factor concentrates, vitamin K, or other corrective treatments)
* Women patient of childbearing potential or male patient must agree to have efficient birth control method from inform consent form signature to 3 months after Selective internal radiation therapy (SIRT) procedure.
Exclusion Criteria:
* Serum platelet count ≤35 000/ mm³.
* History of prior partial splenic embolization, splenectomy or any significant medical history affecting the spleen including medical history of proven cirrhosis with at least one episode of decompensation in the last 6 months from enrolment.
* Any non-Chemotherapy-Induced Thrombocytopenia and/or Chemotherapy-Induced Thrombocytopenia without splenomegaly (as per example, but not limited to, thrombocytopenia related to bone marrow toxicity)
* Use of any treatment known to increase platelet count 1 month prior to Baseline.
* History of severe peripheral allergy or intolerance to contrast agents, narcotics, sedatives or atropine that cannot be managed medically.
* Contraindications to angiography and selective visceral catheterization (bleeding, diathesis or coagulopathy that is not correctable by usual therapy or hemostatic agents).
* Spleen anatomy and/or splenic arterials anatomy and/or technical constraints identified during screening test which does not allow safe and/or ability to deliver the planned target dose/activity of TheraSphere
* Serum platelet count ≤35 000/ mm³.
* History of prior partial splenic embolization, splenectomy or any significant medical history affecting the spleen including medical history of proven cirrhosis with at least one episode of decompensation in the last 6 months from enrolment.
* Any non-Chemotherapy-Induced Thrombocytopenia and/or Chemotherapy-Induced Thrombocytopenia without splenomegaly (as per example, but not limited to, thrombocytopenia related to bone marrow toxicity)
* Use of any treatment known to increase platelet count 1 month prior to Baseline.
* History of severe peripheral allergy or intolerance to contrast agents, narcotics, sedatives or atropine that cannot be managed medically.
* Contraindications to angiography and selective visceral catheterization (bleeding, diathesis or coagulopathy that is not correctable by usual therapy or hemostatic agents).
* Spleen anatomy and/or splenic arterials anatomy and/or technical constraints identified during screening test which does not allow safe and/or ability to deliver the planned target dose/activity of TheraSphere
* History of bleeding disorder attributed to another cause other than thrombocytopenia (e.g., thrombopathy, coagulation disorder, gastric bleeding related to portal hypertension etc..) within 2 months of enrolment and/or any active bleeding disorder.
* Any serious medical condition likely to impede successful completion of the study, such as certain mental disorders, cardiac arrhythmias, uncontrolled congestive heart failure or respiratory disease and any toxicity from a prior treatment incompatible with the performance of the procedure. Comorbidities or Investigator judgement of poor overall health status which may make the patient a poor candidate for locoregional treatment.
* Female patients who are pregnant or breastfeeding or male or female patients of reproductive potential who are not willing to employ effective birth control from ICF signature to 3 months after SIRT.
* Person not affiliated or not beneficiary of a social security scheme and/or
* Persons deprived of their liberty by a judicial or administrative decision, persons subject to psychiatric care under articles L. 3212-1 and L. 3213-1 who are not covered by the provisions of Article L. 1121-8 and persons admitted to a health or social establishment for purposes other than research, including:
* Pregnant, parturient, breast-feeding women
* Minors (see also inclusion criterion 1)
* Persons receiving psychiatric treatment
* Persons admitted to a health or social establishment for purposes other than research
* Person of full age under curatorship
* Adult subject to a mandate for future protection, a family authorization, or a guardianship measure
* Any contraindications to perform standard spleen SIRT procedure (for example, but not limited to splenic artery catheterization contraindication; such as patients with vascular abnormalities or bleeding diathesis; contraindications to vaccination, etc.)
* Patients with persistent coagulation abnormalities in the following scenarios:
* Severe hepatic disease, where the production of coagulation factors is significantly impaired and cannot be corrected by standard treatments.
* Coagulopathy induced by anticoagulants (e.g., direct oral anticoagulants or warfarin), where correction is not possible due to treatment instability or poor response to antidotes.
* Severe hemostatic dysfunction, where correction is not achieved despite appropriate intervention to restore coagulation balance.
* Patients with Tc-99m MAA splenic arterial perfusion scintigraphy shows:
* any extra splenic uptake that may not be corrected by angiographic techniques. Any visual extra-splenic uptake that cannot be corrected by angiographic techniques.
* lung shunt that could result in the delivery of a dose greater than 30 Gy to the lungs
