Bone metastasis is a secondary malignancy in which a primary tumor outside the bone metastasizes to the bone and is the most common bone malignancy, with an incidence 25 times higher than that of primary sarcoma of the bone. Approximately 15% of cancers clinically present with bone metastases. Among all bone metastases, 85% are from breast, prostate, kidney, lung and thyroid. The age of onset is more than 50 years old and there is no significant difference in gender.
[Etiology and pathology
The process of metastasis includes: the primary tumor cells detach, erode and enter the blood vessels and/or lymphatic vessels, then reach the bones through the circulation, stay and implant, proliferate to form new lesions, and appear as bone metastases.
[Clinical manifestations].
Most patients with bone metastases have a history of the primary tumor. Most bone metastases are asymptomatic and many are discovered incidentally during routine physical examination after primary tumor surgery. Pathological fracture is often the first symptom of bone metastases. Some present with diffuse bone pain, and spinal metastases present with back pain and an occasional soft tissue mass with tenderness. Prior to this, there are no conscious symptoms and no pain for months or years. The pain begins intermittently and becomes constant, and is not relieved by rest or braking. Late stages of metastases are characterized by depression, wasting, weakness, anemia and hypothermia. Hypercalcemia is one of the causes of death in bone metastases. Malignant hypercalcemia can cause abdominal pain, intractable vomiting, extreme weakness, severe dehydration, rapid onset of renal failure, coma, and death.
Auxiliary examination
1.X-ray examination of early cancellous bone metastases does not cause destruction of bone trabeculae, but as the disease progresses, the tumor destroys the adjacent bone trabeculae, resulting in indistinct, patchy, chisel-like osteolytic destruction. The bone trabeculae around the lesion produce reactive bone and show increased radiographic density. Pathological fracture is a common complication of bone metastases, and is often seen in high stress areas, such as femoral neck, humeral neck, and spine.
2. Radionuclide scan. Radionuclide scan is the most reliable method to assess systemic skeletal metastases. Metastatic lesions usually have increased nuclide uptake changes.
3.CT scan. CT scan can show the erosive and soft tissue mass characteristics of the metastases. Enhanced CT images can show the hematologic features of the lesion and the adjacent vascular-neural structural changes.
4.MRI examination. Osteolytic lesions show low signal on T1-weighted images and high signal on T2-weighted images. Bone metastatic lesions involve the surrounding soft tissues less frequently. Osteogenic bone metastases are less common, and they show low signal on T1-weighted and T2-weighted images.
5.Pathological examination.
(1) Visual observation. The area of osteolytic destruction of the lesion consists of grayish-white solid tumor tissue. At the edge of the tumor encroaching on cancellous bone, the medullary cavity is replaced by red, soft tissue that fills the intact cancellous bone gap.
When the lesion is composed of well-differentiated adenocarcinoma, the tissue has a soft, glandular appearance. When the lesion is composed of poorly differentiated mesenchymal and fibrous connective tissue-dominated tumors, the tissue has a grayish, fleshy appearance. Metastases from melanoma have a distinct dark black appearance.
(2) What is seen microscopically. Well-differentiated metastatic adenocarcinoma cells are arranged in a glandular pattern. In some lesions, the cell arrangement is highly suggestive of their organ origin (e.g., thyroid, kidney), but in most cases, the arrangement is featureless (breast, prostate, gastrointestinal tract, uterus, testis, lung) and does not suggest a specific organ origin. Metastatic squamous cell carcinoma has the characteristics of common squamous cell carcinoma, where the fibrous tissue of the host with varying degrees of maturation is the main structure, and tumor cell masses are scattered in the fibrous structures.
【Diagnostic points】.
1.History of primary cancer.
2.Clinically, there is diffuse bone pain, or soft tissue mass.
3.X-ray shows indistinct border, patchy chisel-like osteolytic destruction, or “osteogenic” changes with increased radiological density around the lesion. Pathological fracture may occur.
4.The tracing lesion shows increased nuclide uptake and can detect incomplete metastases on x-ray.
5.Pathological examination can reveal the histological characteristics of the primary cancer.
[Differential diagnosis
Myeloma: It is a primary systemic bone marrow tumor with the age of onset mostly from 40 to 70 years old, and the preferred sites are spine (vertebrae), flat bone (pelvis, skull and ribs). The initial radiographic presentation is diffuse osteopenia, followed by areas of unresponsive bone with poorly defined osteolytic destruction and no periosteal reaction. These are identical to those of bone metastases. The main differentiating points are that bone metastases rarely develop below the elbow or knee, and immunoglobulin electrophoresis is mostly unremarkable. However, pathologic histology is required to confirm the final diagnosis.