Bone tumors may be malignant or benign. The age of onset, as well as prognosis, markedly depend on the underlying subtype.
Benign bone tumors are generally asymptomatic, whereas progressive bone pain at the site of the lesion, accompanied by swelling and typically occurring during the night or at rest, is characteristic for bone sarcomas  . In some cases, a palpable mass may be observed during physical examination , in which case a thorough diagnostic workup is necessary.
Plain radiography of the site of pain is a good initial method to confirm the presence of a tumor . Irregular borders of identified lesions, areas of bone destruction and extension into soft tissues are main signs of malignant tumors, while sharply demarcated lesions may be suggestive of benign tumor growth . More advanced imaging studies, such as computed tomography (CT) or magnetic resonance imaging (MRI) should be performed to further assess the tumor. A definite diagnosis, however, is made by biopsy . It is imperative to determine the exact type of the lesion in order to design the optimal therapeutic approach, as different strategies may be employed.
Chemotherapy (doxorubicin, high-dose methotrexate, cisplatin, ifosfamide) followed by wide surgical resection is the recommended strategy for osteosarcoma and Ewing sarcoma. Various reconstructive surgeries - use of allografts, vascularized autografts or megaprostheses can be performed to repair the damaged extremities, pelvis or the spine  . Some tumors, such as chondrosarcomas, are resistant to chemotherapy and surgical excision only is recommended  . The significant percentage of benign tumors require surgery as well due to the potential for malignant transformation   .
The prognosis depends on the nature of the tumor (benign or malignant) and the underlying subtype. Benign tumors generally carry a good prognosis and the majority of cases are discovered incidentally, while malignant tumors carry varying survival rates. Namely, 5-year survival is achieved in 70% of patients with localized osteosarcoma, but only 20% of patients will survive 5 years in the setting of metastatic disease , suggesting that an early diagnosis is detrimental for the better outcome of patients. In fact, a lack of clinical suspicion is the primary reason why bone tumors are diagnosed late .
The literature describes eight types of benign bone tumors - osteoma, benign giant cell tumor, osteoid osteoma, osteoblastoma, osteochondroma, aneurysmal bone cyst, fibrous dysplasia and enchondroma . Bone sarcomas, primarily osteosarcoma and Ewing sarcoma are malignant forms and the pathogenesis primarily includes genetic mutations that cause aberrant growth and formation of tumor cells. On the basis of their morphological characteristics, bone tumors can be bone-forming, cartilage-forming, or fibrous tissue forming .
It is estimated that approximately 3,300 new cases of malignant bone and joint tumors will appear in the United States yearly and on the basis of these findings, they are one of the rarest groups of malignancies encountered in clinical practice . In fact, malignant bone tumors (bone sarcomas) account for only 0.2% of all cancers . A mild predilection toward male gender is observed  and they develop in two peaks - during the second decade and in patients older than 60 years . Risk factors include the presence of familial syndromes (Ollier's disease and Maffucci syndrome, familial retinoblastoma and Rothmund Thomson syndrome) and benign tumors or bone-related conditions that predispose to malignant tumor formation (osteochondromas, giant cell tumor, chondroblastoma, fibrous dysplasia, osteoblastoma, Paget's disease) . Radiation, chronic osteomyelitis, bone infarcts, and prosthetic implants have also been described as contributing factors  .
A range of genetic mutations have been identified in the pathogenesis of bone tumors - EXT1 and EXT2 tumor suppressor gene mutations in osteochondromas, translocations of the Ewing sarcoma (EWS) gene with ETS transcription factor gene, inactivation of p53 and aberrations in RB1 gene are some of the most important  . Their triggers, however, remain unknown.
Bone malignant tumors are rarely encountered in clinical practice, as primary bone malignancies (bone sarcomas) comprise about 0.2% of all cancers . In addition to malignant, several benign tumors have been described, most common being osteochondroma, benign giant cell tumor, osteoma, and osteoid osteoma, which are more frequently encountered than their malignant counterparts . Metastatic tumors also represent an important group of bone malignancies . The age of onset markedly varies depending on the subtype while gender predilection has not been established . Benign lesions are often discovered incidentally as they are frequently asymptomatic, but bone pain occurring at rest or during the night is recognized as the most important symptom of malignant tumors . The diagnosis is made by radiographic studies and biopsy, while treatment depends on staging and includes surgery, radiotherapy, chemotherapy and molecular therapy .
Malignant bone tumors represent a very rare group of cancers, with approximately 3,300 cases occurring in the United States every year There are malignant and benign bone tumors. Malignant bone tumors (osteosarcomas and Ewing sarcoma) most frequently appear in childhood and in adults over 60 years, while benign tumors can develop throughout childhood and adulthood and virtually any bone of the body may be a potential site. Benign tumors are predominantly asymptomatic, whereas bone pain during the night or at rest is the main symptom of a malignant bone disease. The diagnosis is made by performing an X-ray of the bone which is thought to be the site of tumor growth. Magnetic resonance imaging (MRI), computed tomography (CT scan) and biopsy, however, are necessary to assess the extent of growth and determine the underlying subtype, respectively. Treatment may include surgical removal, chemotherapy, and/or radiotherapy, and the prognosis directly depends on the time of diagnosis, as tumors are more effectively treated in early stages.