Bone metastases

Definition

Bone metastases are secondary malignant foci in bone tissue due to the spread of cancer cells from the primary tumor of another organ. They are manifested by increasing pain, hypercalcemia, and pathologic fractures. In some cases, a dense tumor-like formation may be found in the affected area. The compression of large vessels provokes circulatory disorders, as well as the compression of nerve trunks, which leads to neurological symptoms. Diagnosis is established based on anamnesis, complaints, objective examination data, and results of laboratory and instrumental studies.

General information

Bone metastases – bone tissue lesions resulting from the spread of malignant cells with the blood or lymphatic flow. They occur in the late stages of cancer. 80% of secondary bone tumors are detected in breast cancer and prostate cancer. In addition, metastasis to bone is not uncommon in thyroid malignancies, lung cancer, malignant tumors of the kidney, sarcoma, lymphoma, and lymphogranulomatosis. For other neoplasms, bone lesions are less characteristic. 

Types of bone metastases

Bone tissue constantly undergoes resorption and bone formation processes, which are generally balanced. Malignant cells in metastasis disrupt this balance by overactivating osteoclasts (cells that destroy bone tissue) or osteoblasts (young cells of new bone tissue). Considering the predominant activation of osteoclasts or osteoblasts, two types of bone metastases are distinguished: osteolytic, in which the destruction of bone tissue predominates, and osteoplastic, in which thickening of the bone area is observed. 

Usually, secondary foci are detected in bones with a rich blood supply: in the spine, ribs, pelvic bones, skull bones, femur, and humerus. In the initial stages of bone metastases may be asymptomatic. Subsequently, they are accompanied by increasing pain. Over time, the pain becomes excruciating and intolerable, and the condition of patients is relieved only after taking narcotic analgesics.

Sufficiently large bone metastases can cause visible deformity, be detected on palpation as a tumor-like mass, or be seen on radiographs as an area of destruction. A severe complication of bone metastases are pathologic fractures, in 15-25% of cases occurring in the area of tubular bones, in almost half of cases – in the area of vertebrae. Sometimes, in the process of growth, metastases in the bones squeeze nearby large vessels or nerves. There are circulatory disorders in the first case; in the second case, there are neurological disorders. 

Symptoms of bone metastases

Hypercalcemia

Hypercalcemia is a life-threatening complication found in 30-40% of patients with bone metastases. It is caused by increased activity of osteoclasts, which causes the amount of calcium that exceeds the kidneys’ excretory capacity to enterthe blood from the destroyed bone. Patients with bone metastases have hypercalcemia and hypercalciuria, which disturbs the process of reverse absorption of water and sodium in the renal tubules. Polyuria develops.

Hypercalcemia in bone metastases causes disorders of various organs and systems. CNS disorders, lethargy, affective disorders, proximal myopathy, confusion, and loss of consciousness are also observed. In the cardiovascular system, a decrease in blood pressure, heart rate, and arrhythmia are detected. Cardiac arrest is also possible. In the gastrointestinal tract, nausea, vomiting, constipation, and appetite disorders are noted. In severe cases, pancreatitis or intestinal obstruction develops.

Pathologic fractures

Pathologic fractures occur when over 50% of the cortical layer is destroyed. They are most often detected in vertebrae; the second most common are femur fractures, usually in the neck or diaphysis. A distinctive feature of pathologic spine fractures with bone metastases is the diversity of lesions (simultaneously revealed violation of the integrity of several vertebrae. The cause of pathologic fracture in bone metastases can be a minor traumatic impact, for example, a weak blow or even an awkward turn in bed. Sometimes, such fractures appear spontaneous, arising without any external causes.

Spinal cord compression

Spinal cord compression is detected in 1-5% of patients with metastatic spinal lesions. In 70% of cases, metastases to thoracic vertebrae, in 20% – to lumbar and sacral vertebrae, and in 10% – to cervical vertebrae are the cause of disorders. In bone metastases, acute (when compressed by a bone fragment) and gradually progressive (when compressed by a growing tumor) disorders can be detected. When squeezed by a growing tumor, patients with bone metastases are bothered by increasing pain. Muscle weakness develops, and sensory disturbances are detected. At the final stage, paresis, paralysis, and pelvic organ dysfunction occur.

Diagnosis

Diagnosis is established based on anamnesis (data on the presence of a primary malignant neoplasm), clinical picture, and the results of additional studies. Lack of information about an already diagnosed cancer is not a reason to exclude bone metastases since the primary tumor may be asymptomatic. In the presence of neurologic disorders, a neurologic examination is performed. At the initial stage of examination, scintigraphy is performed. Then, patients are referred to radiography, CT, or MRI of the bone to clarify the nature and prevalence of the lesion. A biochemical blood test is prescribed to detect hypercalcemia.

Treatment of bone metastases

Treatment tactics are determined taking into account the type and location of the primary tumor, the number and location of metastases in the bone, the presence of metastases to other organs and tissues, the presence or absence of complications, age, and general condition of the patient. Surgical interventions are palliative and are indicated in the presence of complications (pathologic fractures, spinal cord compression). Surgery for bone metastases aims to eliminate or relieve pain, restore limb or spinal cord function, and create more favorable conditions for patient care.

When deciding on surgical intervention, prognosis is taken into account. Prognostically favorable factors are slow growth of the primary neoplasm, a long period without recurrence, a small solitary metastasis in the bone, radiological signs of bone sclerosis after conservative treatment, and satisfactory patient condition. In such cases, extensive surgical interventions (installation of plates, pins, Ilizarov apparatus) can be performed.

In case of aggressive growth of the primary neoplasm, frequent recurrences, multiple metastases, especially with simultaneous involvement of internal organs, large size of metastasis to the bones, no signs of sclerosis on radiographs, and unsatisfactory condition of the patient, surgical interventions on tubular bones are not recommended even in the presence of pathologic fracture. 

Emergency treatment for bone metastases complicated by spinal cord compression includes vascular drugs, drugs to improve the metabolism of nervous tissue, and high doses of dexamethasone. In case of nerve tissue compression due to metastasis growth into the bone, decompression laminectomy is performed; in case of spinal cord compression due to pathological vertebral fracture, decompression-stabilizing surgeries are performed: plate fixation or transpedicular fixation, vertebral reconstruction using bone cement, auto- and allografts, etc.

Chemotherapy and radiation therapy for bone metastases are used in combination with conservative therapy in preparation for surgery and in the postoperative period. In hypercalcemia, rehydration is carried out by intravenous infusion of saline solutions. Patients with bone metastases are prescribed loop diuretics (furosemide), corticosteroids, and bisphosphonates. The effect of therapy is maintained for 3-5 weeks, then the course of treatment is repeated.

All these treatment options are available in more than 800 hospitals worldwide (https://doctor.global/results/diseases/bone-metastases). For example, Surgery for bone cancer can be done in 23 clinics across Turkey for an approximate price of $5.5 K (https://doctor.global/results/asia/turkey/all-cities/all-specializations/procedures/surgery-for-bone-cancer). 

Prognosis

The prognosis for bone metastases is more favorable than internal organ metastases. The average life expectancy is two years. The quality and, in some cases, life expectancy depends on the presence or absence of complications, which determines the importance of preventive measures when metastases in the skeleton’s bones are detected. When metastases to the spine, it is recommended to exclude lifting weights and rest several times during the day in a recumbent position. With lesions of the femur during the treatment period, it is advised to maximize the relief of the limb using a cane or crutches. Physical therapy for any bone metastases is contraindicated. Patients need to undergo regular examinations for the timely detection of disease recurrences.