Multimodal Immune Characterization of RAre Soft Tissue Sarcoma - MIRAS Project From SARRA (SARcome RAre) Project of the French Sarcoma Group

Inclusion Criteria: 1. Age ≥18 years at the time of study entry. 2. Diagnosis of one of the following rare sarcoma subtype, confirmed by RRePS network: * Clear Cell Sarcoma (CCS) * Epithelioid Sarcoma (ES) * Perivascular Epithelioid Cell neoplasm (PEComa) * Desmoplastic Small Round Cell Tumours (DSRCT) * Malignant Solitary Fibrous Tumours (mSFT) * Alveolar Soft Part Sarcoma (ASPS) * Epithelioid Hemangioendothelioma (EH) * Low-Grade Fibromyxoid Sarcoma (LGFS) * Sclerosing Epithelioid Fibrosarcoma (SEF). 3. Localized/locally advanced or metastatic disease. 4. In case of localized disease, treatment must not have been yet initiated before inclusion (except surgical excision). 5. In case of metastatic disease, project of new line of systemic treatment must have been decided before inclusion. 6. Patient followed in the center within a standard of care procedure or clinical trial. 7. Archived tumor specimen at initial diagnosis available (before treatment initiation). 8. Evaluable disease (measurable as per RECIST 1.1) or not. 9. ECOG Performance status 0-3. 10. Patient able to participate and willing to give informed consent prior to performance of any study-related procedures. 11. Patient affiliated to a Social Health Insurance in France. Exclusion Criteria: 1. Diagnosis of all other histotypes of soft tissue sarcoma. 2. Any condition contraindicated with procedures required by the protocol. 3. Known history of positive test for hepatitis B virus or hepatitis C virus or human immunodeficiency virus (HIV) or known acquired immunodeficiency syndrome (AIDS). 4. Any psychological, familial, geographic or social situation, according to the judgment of investigator, potentially preventing the provision of informed consent or compliance to study procedure. 5. Pregnant or breast-feeding woman. 6. Patient who has forfeited his/her freedom by administrative or legal award or who is under guardianship.