Bone can be the site of primary malignant tumors or, more commonly, secondary lesions. The most frequent primary tumors are osteosarcoma, chondrosarcoma, and Ewing sarcoma, whereas the malignancies that most commonly metastasize to bone include breast, prostate, lung, kidney, and thyroid cancers.

For the treatment of these conditions-and, in some cases, for locally aggressive benign diseases-a surgical approach is often required, which may result in substantial bone loss. Most commercially available prostheses commonly used in orthopedic surgery are not always suitable, either because of the anatomical location of the procedure or the type of resection planned, and thus the extent of the bone defect to be reconstructed. Therefore, specific prosthetic implants designed for oncologic surgery are required.

For this reason, modular prostheses have been developed, allowing reconstruction of bone defects of varying sizes across different anatomical districts. In recent years, the development and use of 3D-printing technology for producing custom-made prostheses has also increased, with the aim of reconstructing bone defects in areas that are difficult to treat and achieving an accurate reproduction of the patient's anatomy. This technology enables reconstruction in a wide range of skeletal sites. Additionally, it allows for preoperative planning on printed anatomical models and opens the possibility of integrating materials with adjuvant-related properties into the prosthetic design, such as photothermal therapy or antimicrobial features.

Although numerous studies on this topic are available in the literature, they frequently involve small patient cohorts. There is therefore a need to expand case series with longer follow-ups to better assess the reliability and effectiveness of these treatment strategies in the development of reconstructive orthopedic oncologic surgery.

Inclusion Criteria:

• Age between 30 and 70 years;

Diagnosis of primary malignant or locally aggressive benign bone tumors, or secondary bone lesions with a primary diagnosis of breast, lung, prostate, kidney, or thyroid cancer;

Extensive bone loss precluding the use of currently available prostheses or standard surgical techniques;

Use of modular or custom-made prostheses produced with 3D-printing technology; minimum follow-up of 12 months;

(For patients in the retrospective phase) completion of evaluation questionnaires during outpatient follow-ups;

Obtaining Informed Consent, except for deceased patients enrolled in the retrospective phase of the study.

Exclusion Criteria:

Patients with disease spread to other bone segments;

Age <30 years or >70 years;

Patients who have undergone previous surgical procedures on the involved segment;

Follow-up of less than 1 year;

Incomplete clinical or radiological data sets;

Inability to obtain Informed Consent, except for deceased patients enrolled in the retrospective phase of the study

Patients with primary or secondary bone tumors treated at the Policlinico A. Gemelli