**2. Primary malignant tumors**

### **2.1 Giant cell tumor of bone (GCT)**

This tumor accounts for 5% of all primary and 20% of the benign skeletal tumors [8]. GCT is an aggressive osteolytic benign bone tumor developing in the long bones, which is characterized by giant, multinucleated osteoclast-like cells, recruited by stromal cells such as osteoblasts [8, 9]. The stromal cells of GCT highly express parathyroid hormone-related peptide (PTHrP) and thus increase the bone tumor cell local invasiveness and migration [9].

Distal femur, proximal tibia, and distal radius are the most common locations for the occurrence of GCT, but due to its association with Paget's disease, it may also occur in the skull, pelvis, facial bones, and spine. It has been reported to rarely affect greater trochanter of the femur. Though some of the reports claim an equal rate of occurrence in both the genders, some reports show an increased prevalence in females [8].

These tumors have been associated with reduction in length of telomeres [7]. Radiological examination in patients with closed physes displays lytic lesions with well-defined, non-sclerotic margins that are eccentric in location and extend near the articular surface. Thus GCT involves cortical expansion or destruction [8].

#### **2.2 Chondrosarcoma**

Chondrosarcomas majorly involve tumorous growth of chondrocytes, which are mostly found in bones that elongate due to endochondral ossification and involve differentiation in the epiphyseal growth plates of long bones. For example, hypertrophic chondrocytes are found in clear cell chondrosarcoma. The most common sites include proximal femur, proximal humerus, distal femur, and ribs. Sex hormones such as estrogen play a major role in governing the nuclear signaling pathways involved in this process of ossification [1].

**15**

*Bone Tumors: Types and Treatments*

prognosis [10].

**2.3 Ewing's sarcoma**

monly in males [11].

weight loss [1].

**2.4 Osteosarcoma**

coma die due to metastasis to lungs [1, 16].

differentiated tumors [10].

*DOI: http://dx.doi.org/10.5772/intechopen.86550*

There are different histologic variants of chondrosarcoma.

1.Mesenchymal chondrosarcomas are highly aggressive tumors, composed of resting chondrocytes, and are radiographically and histologically similar to Ewing's sarcoma [1, 10]. Such sarcomas frequently occur in the pelvic bones, femur, and humerus and less commonly in the head, spine, breast, and prostate [1]. These have high risk of local recurrence and distant metastasis [10].

2.Dedifferentiated chondrosarcomas are aggressive neoplasms and have poor

3.Clear cell chondrosarcomas are low-grade tumors and involve the epiphyseal end of the long bone. The radiographs show a lytic defect at the epiphyseal end

4.Extraskeletal myxoid chondrosarcomas are slow-growing tumors, characterized histologically by prominent myxoid degeneration, and are considered as

5.Juxtacortical chondrosarcoma arises on the surface of the bone and is histologically identical to conventional intramedullary chondrosarcoma [1].

Ewing's sarcoma is an exception to all the bone tumors, because bone tumors are mostly mesenchymal in origin, but Ewing's sarcoma is reported to have neuroectodermal precursor cells [7]. It has been found to be associated with neuroblastomas in patients younger than 5 years, whereas in patients above 30 years, it is associated with small round cell tumors (e.g., small-cell carcinoma) and large-cell lymphoma [1]. Ewing's sarcoma is most likely to occur in younger individuals and most com-

Ewing's sarcoma is characterized by small round cell bone tumor and involves pain at the site of tumor and soft tissue swelling around it [1]. Unlike other primary tumors of the bone, Ewing's sarcoma is associated with a characteristic translocation in the 11th and 22nd chromosomes. This translocation results in production of an aberrant transcription factor EWS/FLI1 that forms a complex with RNA helicase A and drives the pathogenesis of Ewing's sarcoma [7, 11]. Its metastasis involves certain non-specific signs of inflammation, anorexia, fever, malaise, fatigue, and

Osteosarcoma is an osteoid-producing malignancy of mesenchymal origin [12]. It is the third most frequent type of cancer in adolescence and represents more than 56% of all bone tumors [13]. It is the most common bone sarcoma and affects 60% of the patients below 25 years of age and 30% of the patients above 40 years [14, 15]. It is associated with extensive genomic disruptions and propensity of metastatic spread. Seventy-six percent of the osteosarcomas have been found to be associated with reduced expression of *HACE1* gene localized to human chromosome 6q21, thus resulting in poor survival [14]. Approximately, 30–40% children with pediatric osteosar-

Environmental factors such as exposure to radiation, teriparatide (parathyroid hormone 1–34) usage, and consumption of fluorinated drinking water during

of long bones, sharply demarcated with sclerotic margins [10].

*Hormone Therapy and Replacement in Cancer and Aging-Related Diseases*

neoplasm, local tissue invasion, intravasation into blood vessels, extravasation into bone marrow, tumor cell dormancy, proliferation in bone, and modification of bone microenvironment [3]. The site of metastases is governed by the "seed and soil" hypothesis by Paget which states that neoplastic cells grow or proliferate only in a suitable environment [3]. Tumor cells therefore migrate to the heavily vascularized areas of the skeleton, particularly the red bone marrow of the axial skeleton and the proximal ends of the long bones, the ribs, and the vertebral column [5]. Chemotactic factors such as CXCL10 (CXC motif ligand [CXCL]), CXCL12, and osteopontin have been reported to play a major role in tumor migration [6].

Tumors can be classified into low-grade (Grade I), intermediate-grade (Grade II), and high-grade (Grade III) tumors [1]. Grading of bone tumors is roughly based on the cellularity of the lesions compared to the extracellular matrix, nuclear features, the presence of mitotic figures, and necrosis [7]. Grade II tumors are more cellular, with a greater degree of nuclear atypia, hyperchromasia, and nuclear size. Grade III tumors have significant areas of marked pleomorphism, large cells with more hyperchromatic nuclei than Grade II tumors, occasional giant cells, and abundant necrosis [1]. High-grade bone tumors are the fastest growing and most aggressive group of classic osteoblastic subtype. On the basis of histological appearance, bone tumors are classified as parosteal and periosteal. Parosteal tumors belong to lowgrade subtype of osteosarcoma, whereas periosteal belongs to the intermediategrade subtype. Parosteal tumors have fibroblast appearance and are limited to bone

surface, but periosteal tumors appear chondroblastic upon histology.

This tumor accounts for 5% of all primary and 20% of the benign skeletal tumors [8]. GCT is an aggressive osteolytic benign bone tumor developing in the long bones, which is characterized by giant, multinucleated osteoclast-like cells, recruited by stromal cells such as osteoblasts [8, 9]. The stromal cells of GCT highly express parathyroid hormone-related peptide (PTHrP) and thus increase the bone

Distal femur, proximal tibia, and distal radius are the most common locations for the occurrence of GCT, but due to its association with Paget's disease, it may also occur in the skull, pelvis, facial bones, and spine. It has been reported to rarely affect greater trochanter of the femur. Though some of the reports claim an equal rate of occurrence

These tumors have been associated with reduction in length of telomeres [7]. Radiological examination in patients with closed physes displays lytic lesions with well-defined, non-sclerotic margins that are eccentric in location and extend near the articular surface. Thus GCT involves cortical expansion or destruction [8].

Chondrosarcomas majorly involve tumorous growth of chondrocytes, which are mostly found in bones that elongate due to endochondral ossification and involve differentiation in the epiphyseal growth plates of long bones. For example, hypertrophic chondrocytes are found in clear cell chondrosarcoma. The most common sites include proximal femur, proximal humerus, distal femur, and ribs. Sex hormones such as estrogen play a major role in governing the nuclear signaling

in both the genders, some reports show an increased prevalence in females [8].

**2. Primary malignant tumors**

**2.1 Giant cell tumor of bone (GCT)**

tumor cell local invasiveness and migration [9].

pathways involved in this process of ossification [1].

**14**

**2.2 Chondrosarcoma**

There are different histologic variants of chondrosarcoma.

