Cost-effectiveness Evaluation of the Use of a Patient Specific Instrument for Surgical Resection of Malignant Bone Tumor Within the Pelvis Versus the Conventional Surgical Treatment

Screening Critieria: Retrospective group (reference) * Patient already operated for the same indication as detailed in the prospective group inclusion criteria * Surgery date within the 6 years before the study activation in the participating center * Adult (18 years old or more) at the time of surgery Inclusion Criteria: Prospective group (innovation) * Primitive malignant pelvic bone tumor or mixt tumor (primary bone sarcoma, soft tissue sarcoma with bone extension, giant cells tumor of bone and any tumor requiring such a resection) * Indication for a wide monobloc resection according to clinical guidelines of the pathology ("en bloc" resection of iliac bone including a bone section from periacetabular Enneking zone 2 to the sacrum zone 4, hip extra-articular resection for proximal femur tumors and sacral tumor or ilio-sacral tumors that need a vertical osteotomy or horizontal osteotomy above S2) * Ability to fill in Euroqol and TESS questionnaires * Adult (18 years old or more) * Health insurance holder Retrospective group (reference) Patient fulfilling the matching criteria with one patient of the prospective group, according to the following matching criteria (in order of importance): 1. Tumor location (Enneking zones 1, 2, 1-2, 2-3, 1-2-3, 1-2-4, 1-2-3-4, 1-4, sacrum) 2. Tumor type (chondrosarcoma, osteosarcoma, Ewing, chordoma, other tumor type) 3. Surgery center 4. Tumor size (as close as possible between both patients) 5. Response to chemotherapy (good, bad, not applicable). Exclusion Criteria: Prospective group (innovation) * Patient suffering from a local recurrence or a metastasis at recruitment time * Absence of informed consent * Pregnancy or breastfeeding * Minors * Adults under guardianship or trusteeship Retrospective group (reference) * Patient not fulfilling the protocol matching criteria * Refusal to participate