Orthopaedic tumors and masses

 Metastatic carcinoma to bone is 25 times more likely to occur than primary bone sarcoma. The five primary carcinomas that most commonly metastasize to bone are breast, prostate, lung, kidney, and thyroid. In contrast to the small numbers of primary bone sarcoma, there are more than a million new cases of these five carcinomas in the United States every year. Metastatic carcinoma most commonly occurs in the thoracic and lumbar spine (theoretically because of the valveless Batson”s venous system there) but can occur in virtually any bone. It commonly presents as pain and can lead to weakened bone and pathologic fractures (fractures that occur at normal physiologic loads).

 Metastatic breast cancer is common in women with advanced disease. Radiographically, it is classically a mixed lytic and blastic lesion; that is, it causes lysis of bone and formation of bone (Fig. 10-3). It typically responds to radiation therapy but commonly requires surgical stabilization. Metastatic prostate cancer is also radiosensitive but typically is a purely blastic process (Fig. 10-4). Lung, kidney, and thyroid disease usually cause purely lytic and destructive lesions (Fig. 10-5). Renal cell carcinoma and thyroid disease are extremely vascular lesions that often require embolization before open surgical treatment.

 Because of the overwhelming preponderance of potentially metastatic carcinoma, any lytic bone lesion in a patient older than 40 years of age should be considered metastatic disease until proven otherwise. Workup for these patients should include radiographs of the entire affected bone, magnetic resonance imaging (MRI) of the area to assess soft tissue extent, a bone scan to assess other skeletal disease, and a computed tomography (CT) scan of the chest, abdomen, and pelvis in an attempt to identify the primary site (Fig. 10-6). Often a biopsy will still be necessary to secure a definitive tissue diagnosis.

 Surgical treatment of metastatic disease can be challenging. Painful lesions in weight-bearing bones should be aggressively stabilized, but many lesions may not have definite surgical indications, especially in patients with limited life spans. A team approach with medical oncology, radiation oncology, orthopaedic oncology, and the patient should be used to optimize treatment and outcomes. Unfortunately, bone metastasis is an ominous finding with little chance of cure.

 Although much rarer, other malignancies such as melanoma, colon, bladder, and cervical cancer can all metastasize to bone and should be suspected in patients with a positive medical history. Metastatic bone disease in children is not common but can be seen with neuroblastoma and Wilms tumor.

 Multiple myeloma, a malignant disease of monoclonal plasma cells, is the second most common cause of lytic lesions in adults. It is more common in men in their 60s and in African Americans. The bone lesions are well-defined, punched-out lytic areas that can be seen in any bone (Fig. 10-7) and are often seen in the skull. Patients will often have anemia (from bone marrow replacement by tumor), hypercalcemia (from the bone lysis), and a monoclonal protein spike on urine and serum protein electrophoresis. Treatment is multimodal, requiring medical oncology, radiation oncology, and orthopaedics.

 Except for chondrosarcoma (which is seen almost exclusively in adults) the primary sarcomas of bone occur more commonly in the pediatric population. Therefore, entities like osteosarcoma and chondrosarcoma should be considered at the bottom of the differential diagnosis of malignant bone lesions in adults (behind metastatic disease, multiple myeloma, and lymphoma). Primary sarcoma should be at the top of the differential diagnosis of aggressive lesions in children. The primary sarcomas below account for the most common entities.

 Secondary sarcomas of bone are rarely seen but should be considered when there is a lytic lesion or a mass in a bone with preexisting Paget”s disease or previous radiation therapy (osteosarcoma is the most common variant). Enchondromas and osteochondromas can transform into chondrosarcomas less than 1% of the time. Rarely, secondary sarcomas can arise from bone infarcts or fibrous dysplasia.

 Osteosarcoma is the most common primary sarcoma of bone. It is a high-grade disease that has a bimodal age distribution; it arises mostly in children but also in the elderly (often secondary to a preexisting condition like Paget”s disease). It can occur in any bone but is most common around the knee. Radiographically, it is classically a mixed lytic and blastic lesion with a soft tissue mass characterized by a “sunburst,” radial pattern of osteoid formation (Fig. 10-8). Pathologically, the tumor is required to have malignant cells producing osteoid (Fig. 10-9).

 The workup for osteosarcoma should include an MRI of the entire bone to assess tumor extent (Fig. 10-10), assist with preoperative planning, and rule out any skip metastases (anatomically separate areas of tumor in the same bone); a CT scan of the chest to evaluate the lungs for metastatic disease (the most common site); and a bone scan to evaluate the skeleton (the second most common site of metastatic disease). A biopsy performed by the treating physician is the next step to secure the diagnosis.

 Treatment for osteosarcoma is typically multidrug chemotherapy, followed by wide excision of the lesion (80% to 90% of cases are limb salvage; see Fig. 10-11), followed by more chemotherapy. Five-year survival rates are currently approaching 80%. Chemotherapy can have ototoxic and cardiotoxic side effects.

 Ewing’s sarcoma is the second most common primary sarcoma in children. Pathologically, it is a high-grade tumor composed of monotonous, small round blue cells (Fig. 10-12). The majority of Ewing”s sarcomas have a characteristic t(11,22) translocation that results in the formation of the EWS-FLI1 oncogene.

 Ewing’s sarcoma is often seen in flat bones and the metaphyseal-diaphyseal regions of long bones. Classically, it has an “onion skin” appearance (multiple thin layers of periosteal reaction at the site of the tumor; see Fig. 10-13). The workup for Ewing sarcoma is the same as for osteosarcoma, but the prognosis is slightly worse. Treatment involves chemotherapy and local treatment. Most tumors are surgically excised, but because Ewing sarcoma is sensitive to radiation, it can be used to treat tumors that are otherwise unresectable.