**2. Bone tumors**

Bone tumors are characterized by abnormal growth of tissue, which appears and develops into a defined tissue. In the musculoskeletal system, tumors can develop in both bone and soft tissue. Primary tumor lesions at the bone level are relatively infrequent, presenting an incidence of 0.2% of all malignant tumors in the body and preferentially affecting adolescents and young people [6]. Bone tumors can be benign or malignant and within these, primary or metastatic.

The most common bone tumors are bone metastases, multiple myeloma, and primary malignant bone tumors. The most common malignant bone tumor in adults is metastasis from lung, breast, and prostate carcinomas. These appear in advanced stages of the disease and mark a reduction in survival [6, 7]. There are three common primary bone sarcomas, Osteosarcoma, Ewing's Sarcoma, and Chondrosarcoma.

At the time of diagnosis, 15–20% of patients have metastases, of which 90% are pulmonary. This determines a significant drop in patient survival, which can reach 20 25% at 5 years. Once diagnosed, treatment is classically based on neoadjuvant polychemotherapy, surgery, adjuvant polychemotherapy, and eventually radiotherapy. Survival has increased dramatically thanks to polychemotherapy based on different drugs. Tumor reduction induced by polychemotherapy makes limb preservation possible, using conservative surgery techniques; sometimes complex, which guarantee a satisfactory reception from the oncological point of view. When the surgical margins achieved are not satisfactory, radiotherapy could be considered [8, 9].

### **2.1 Osteosarcoma**

Osteosarcoma is defined according to the WHO as a malignant tumor characterized by the formation of bone or osteoid substance by tumor cells. After myeloma, osteosarcoma is the most common primary bone tumor. It represents about 20% of malignant tumors and about twice as many cases as Ewin's sarcoma and chondrosarcoma [6]. Its clinical presentation is variable depending on the type, location, and age of the patient. It generally affects more men than women, between the ages of 10 and 25, with a higher peak in the second decade of life. It is very rare under 5 years of age. There is a second peak of incidence in people older than 35 years; almost always related to previous processes such as Paget's disease, fibrous dysplasia, or irradiation [7].

This malignant neoplasm is characterized by forming bone or osteoid substance directly and encompasses a wide variety of lesions that differ in their clinical and
