Pasireotide as Maintenance Treatment in Synovial Sarcoma and Desmoplastic Small Round Cell Tumor

Inclusion Criteria: Patients meeting all of the following criteria are considered for enrolment into the trial: 1. Reference pathological proven diagnosis of DSRCT in any stage; or Reference pathological proven diagnosis of SySa, IRS III, metastatic or relapsed disease 2. High SSTR2/3/5 mRNA expression, as determined by RNA sequencing in the DKFZ/NCT/DKTK MASTER (ClinicalTrials.gov ID: NCT05852522) or INFORM programs. 3. Stable disease, partial or complete response after completion of standard treatment 4. Age from 13 to 50 years 5. For patients (≥16 years): Karnofsky-Index ≥ 80% For patients (\<16 years): Lansky-Index ≥ 80% 6. No curative treatment option 7. Bodyweight ≥ 30kg and BSA ≥ 1.1m² 8. Time from last chemotherapy (at least 2 chemotherapy cycles) to enrollment \<8 weeks 9. Ability of patient to understand character and individual consequences of the clinical trial 10. Written informed consent (for individuals \<18 years of age an ICF for adolescents and their parents is needed) 11. For women of childbearing potential negative urine pregnancy test at screening as well as highly effective forms of contraception have to be in place thereafter * Evidence of childbearing potential is defined as fertile, following menarche and until becoming post-menopausal unless permanently sterile * Postmenopausal or evidence of non-childbearing status is defined as: * Amenorrhea for 1 year or more without an alternative medical cause following cessation of exogenous hormonal treatments plus follicle stimulating hormone (FSH) levels in the postmenopausal range in women not using hormonal contraception or hormonal replacement therapy. * Chemotherapy-induced menopause * Surgical sterilization (bilateral oophorectomy, bilateral salpingectomy, total hysterectomy or tubal ligation at least 6 weeks before IMP treatment) * A man is considered fertile after puberty unless permanently sterile by bilateral orchidectomy 12. Female patients of childbearing potential and male patients with partners of childbearing potential who are sexually active must agree to the use of two forms of contraception in combination (male condom and one highly effective method). These should be started immediately after signing the informed consent form and continued throughout the period of study treatment plus 3 months for female and male patients . Male patients should refrain from fathering a child or donating sperm during the trial and for at least 3 months following the last dose. 13. Adequate bone marrow, renal, and hepatic function defined by laboratory tests within 14 days prior to study treatment: * Hemoglobin ≥ 10 g/dl * Neutrophil count ≥ 1,500/mm3 * Platelet count ≥ 100,000/µl * Bilirubin ≤ 1.5 x upper limit of normal (ULN) * ALT and AST ≤ 2.5 x ULN * Alkaline phosphatase ≤ 2.5 x ULN * PT-INR/PTT ≤ 1.5 x ULN * Albumin ≥ 25 g/l * Creatine kinase ≤ 2.5 x ULN * Serum creatinine \< or = 1.5 mg/dl or creatinine clearance = or \> 51 ml/min (calculation according to Crockroft-Gault) Exclusion Criteria: Patients presenting with any of the following criteria are not included in the trial: 1. History of hypersensitivity to the investigational medicinal product or to any drug with similar chemical structure or to any excipient present in the pharmaceutical form of the investigational medicinal product 2. Concurrent or previous treatment within 30 days in another interventional clinical trial / Participation in other ongoing clinical trials. 3. Uncontrolled concurrent disease, in particular diabetes mellitus 4. Bleeding disorder 5. Therapeutic anticoagulation which cannot be paused temporarily in order to ensure safe intramuscular injection 6. Is taking or requiring any of the prohibited medication listed in Table 5 (6.4.2) 7. Heart rate at rest \< 60/min 8. fasting glucose level \> 110mg/dl 9. Severe neurologic or psychiatric disorder 10. Pregnancy/lactation 11. Prior treatment with somatostatin analog \-