Metastatic Bone Disease

METASTATIC BONE DISEASE

Metastatic bone disease (secondary bone tumor) is more com-mon than any primary bone tumor. Tumors arising from tissues elsewhere in the body may invade the bone and produce localized bone destruction (lytic lesions) or bone overgrowth (blastic le-sions). The most common primary sites of tumors that metasta-size to bone are the kidney, prostate, lung, breast, ovary, and thyroid. Metastatic tumors most frequently attack the skull, spine, pelvis, femur, and humerus and involve more than one bone (polyostotic).

Pathophysiology

A tumor in the bone causes the normal bone tissue to react by os-teolytic response (bone destruction) or osteoblastic response (bone formation). Primary tumors cause bone destruction, which weakens the bone, resulting in bone fractures. Adjacent normal bone responds to the tumor by altering its normal pattern of re-modeling. The bone’s surface changes, and the contours enlarge in the tumor area.

Malignant bone tumors invade and destroy adjacent bone tis-sue. Benign bone tumors, in contrast, have a symmetric, con-trolled growth pattern and place pressure on adjacent bone tissue. Malignant invading bone tumors weaken the structure of the bone until it can no longer withstand the stress of ordinary use; pathologic fracture commonly results.

Clinical Manifestations

Patients with metastatic bone tumor may have a wide range of as-sociated clinical manifestations. They may be symptom free or have pain (mild and occasional to constant and severe), varying degrees of disability and, at times, obvious bone growth. Weight loss, malaise, and fever may be present. The tumor may be diag-nosed only after pathologic fracture has occurred.

With spinal metastasis, spinal cord compression may occur. It can progress rapidly or slowly. Neurologic deficits (eg, progressive pain, weakness, gait abnormality, paresthesia, paraplegia, urinary retention, loss of bowel or bladder control) must be identified early and treated with decompressive laminectomy to prevent permanent spinal cord injury.

Assessment and Diagnostic Findings

The differential diagnosis is based on the history, physical exam-ination, and diagnostic studies, including computed tomogra-phy, bone scans, myelography, arteriography, MRI, biopsy, and biochemical assays of the blood and urine. Serum alkaline phos-phatase levels are frequently elevated with osteogenic sarcoma. With metastatic carcinoma of the prostate, serum acid phos-phatase levels are elevated. Hypercalcemia is present with breast, lung, or kidney cancer bone metastases. Symptoms of hyper-calcemia include muscle weakness, fatigue, anorexia, nausea, vomiting, polyuria, cardiac dysrhythmias, seizures, and coma. Hypercalcemia must be identified and treated promptly. Surgi-cal biopsy is performed for histologic identification. Extreme care is taken during biopsy to prevent seeding and resultant recurrence after excision of the tumor.

Chest x-rays are performed to determine the presence of lung metastasis. Surgical staging of musculoskeletal tumors is based on tumor grade and site (intracompartmental or extracompart-mental), as well as on metastasis. Staging is used for planning treatment.

During the diagnostic period, the nurse explains the diagnos-tic tests and provides psychological and emotional support to the patient and family. The nurse assesses coping behaviors and en-courages use of support systems.

Medical Management

PRIMARY BONE TUMORS

The goal of primary bone tumor treatment is to destroy or remove the tumor. This may be accomplished by surgical excision (rang-ing from local excision to amputation and disarticulation), radia-tion therapy if the tumor is radiosensitive, and chemotherapy (preoperative, intraoperative [neoadjuvant], postoperative, and adjunctive for possible micrometastases). Major gains are being made in the use of wide bloc excision with restorative grafting technique. Survival and quality of life are important considera-tions in procedures that attempt to save the involved extremity.

Limb-sparing (salvage) procedures are used to remove the tumor and adjacent tissue. A customized prosthesis, total joint arthroplasty, or bone tissue from the patient (autograft) or from a cadaver donor (allograft) replaces the resected tissue. Soft tis-sue and blood vessels may need grafting because of the extent of the excision. Complications may include infection, loosening or dislocation of the prosthesis, allograft nonunion, fracture, devi-talization of the skin and soft tissues, joint fibrosis, and recur-rence of the tumor. Function and rehabilitation after limb salvage depend on positive encouragement and reducing the risk for complications.

Surgical removal of the tumor may require amputation of the affected extremity, with the amputation extending well above the tumor to achieve local control of the primary lesion.

Because of the danger of metastasis with malignant bone tu-mors, combined chemotherapy is started before and continued after surgery in an effort to eradicate micrometastatic lesions. The goal of combined chemotherapy is greater therapeutic effect at a lower toxicity rate with reduced resistance to the medications. There is an improved long-term survival rate when a localized os-teosarcoma is removed and chemotherapy is initiated. Soft tissue sarcomas are treated with radiation, limb-sparing excision, and adjuvant chemotherapy.

METASTATIC BONE DISEASE

The treatment of metastatic bone cancer is palliative. The thera-peutic goal is to relieve the patient’s pain and discomfort while promoting quality of life.

If metastatic disease weakens the bone, structural support and stabilization are needed to prevent pathologic fracture. At times, large bones with metastatic lesions are strengthened by prophy-lactic internal fixation. Internal fixation of pathologic fractures, arthroplasty, or methylmethacrylate (bone cement) reconstruc-tion minimizes associated disability and pain. Patients with met-astatic disease are at higher risk for pulmonary congestion, hypoxemia, deep vein thrombosis, and hemorrhage than are other patients after orthopedic surgery.

Hypercalcemia results from breakdown of bone. It needs to be recognized promptly. Treatment includes hydration with IV ad-ministration of normal saline solution, diuresis, mobilization, and medications such as bisphosphonates, pamidronate, and cal-citonin. Because inactivity leads to loss of bone mass and in-creased calcium in the blood, the nurse assists the patient to increase activity and ambulation.

Hematopoiesis is frequently disrupted by tumor invasion of the bone marrow or by treatment (chemotherapy or radiation). Blood product transfusions restore hematologic factors. Pain can result from multiple factors, including the osseous metastasis, surgery, chemotherapy or radiation side effects, and arthritis. Pain must be assessed accurately and managed with adequate and ap-propriate opioid, nonopioid, and nonpharmaceutical interven-tions. External beam radiation to involved metastasis sites may be used. Patients with multiple bony metastases may achieve pain control with systemically administered “bone-seeking” isotopes (eg, strontium 89).

Additional therapies are used to treat the original cancer. Ra-diation and hormonal therapy may be effective in promoting healing of osteolytic lesions. Chemotherapy is used to control the primary disease.