The incidence of primary cancers that spread to the bone is as follows: prostate 230110, breast 217440, lung, 173770, kidney 35710 and thyroid, 23600 (Jacofsky, 2004, p. 22). These together contribute to 85% of the metastatic bone cancers. The number of people expected to die from cancers per year is 565650. The five year survival rate has risen from 50% in 1975-1977 to 66% in the period 1996-2003 (Cancer Facts and Figures, 2008, p. 2). The improvement shows the progress in diagnosis which is possible at an earlier stage through screening and improvements in treatment.
Though anyone can develop cancer, the middle aged and older adults are more prone. 77% of cancers occur in persons 55 years and older (Cancer Facts and Figures, 2008, p. 1). Bone metastasis is the commonest complication of malignancy that can occur in the bone of Man apart from hypercalcemia of malignancy and oncogenic osteomalacia. Metastatic bone disease is a painful condition that occurs along with cancers of the breast, prostate, lung, or other organs (DeBois, 2002, p. 217).
Though the skeleton receives only 10% of the cardiac output, the metastases are common in the bone. The axial skeleton is the most commonly affected. The third most common site for metastasis is the bone, following on the lungs and liver. 80% of skeletal metastases come from the primary cancers of the breast, prostate, lung, kidney and thyroid (Jacofsky, 2004, p. 21). Among the 1. 4 million newly diagnosed cancers, half would metastasise to bone. The predilection is for the axial skeleton probably because of the venous plexus known as the Batson’s plexus.
Specific sites are the vertebral column or spine, the skull and skull base as the temporal bone, ribs , the extremities (long bones) especially the proximal femur and the bones in the hand and foot (acral). The chance of metastatic cancers occurring has increased with the progress in management. The skeletal metastases rates have reached 70%. If the five primary cancers of breast, prostate, lung, kidney and thyroid are considered, this figure becomes 85% (Jacofsky, 2004, p. 21). The lifetime risk of developing cancer for a male in US is 1 in 2 while it is 1 in 3 for a female.
1437180 new cancer cases are expected to have been diagnosed in 2008. Diagnostic Methods Radiologic appearance Radiographs are the first step in the imaging for diagnosis (Jacofsky et al, 2004, p. 22). Further interpretations with the technetium bone scan may be based on the radiographic image as the technetium scans may not distinguish between malignant and non malignant abnormalities. The same non malignant features which are difficult to diagnose in the scan will be well differentiated in the radiographic image. However it is not foolproof in that 40% of lesions would be missed. A lesion of 1.
5 cm or less may also have to be watched. Metastatic bone cancers are classified by their radiologic appearance into osteolytic and osteoblastic. Metastasis has both the processes of bone destruction and bone formation. All the primary tumors which metastasize to bone produce osteolytic lesions except for the prostate. Some show a mixture of lesions. 15% of the breast cancer bone metastasis show osteoblastic lesions which imply disorganized new bone formation (Guise, 1998). Physiologically the most important factor in the metastasis is the stimulation of bone cells by the tumor cells.
Bone scans and radiographs assist in making the diagnosis. Biochemical markers show the increased bone resorption and formation (Fontana, 2000). Scintigraphic bone scans which use radionuclide complexes with bone-seeking bisphosphonates are useful for localizing osteoblastic metastases (Berruti, 2002). Primary sarcomas are characterized by periosteal reactions with Codman’s triangle and sunburst reaction. Primary sarcoma must not be misdiagnosed for a metastasis as the correct diagnosis will be determining the loss or salvage of a limb (Jacofsky, 2004, p.
22). Biochemical markers in radiological diagnosis Bone matrix has Type I collagen as a major component. Soluble pro-peptide fragments are released when the collagen is biosynthesized by the osteoblast (Clines, 2005, p. 158). These fragments are the markers of new bone formation and osteoblastic activity. Osteoclastic activity produces fragments from cross-linked collagen which are also markers of bone destruction. Monitoring active bone remodeling and the patient’s response to treatment are done by using the biochemical markers.
Bone formation is marked by bone-specific alkaline phosphatase and serum procollagen I amino-terminal propeptide (PINP) and bone resorption by urinary collagen cross-linked N-telopeptide (NTX), collagen I carboxy-terminal telopeptide (CTX), pyridinolines (PYD), and deoxypyridinolines (DPYD). Prostate cancer metastasis shows an increase in both markers (Clines, 2005, p. 158). Adjuvant therapy and chemotherapy could also produce an increase in the markers of resorption and must be remembered when the diagnosis is made and the possibility of metastasis is being investigated.
Technetium Bone Scan The work-up of a patient with known primary cancer with suspected metastatic disease of the bone would require the use of the Technetium scan (Jacofsky, 2004, p. 23). Radioisotope tracer Tc 99m methylene diphosphonate uptake by the tumor cells is noted in the scan. Singular lesions may have to be confirmed as only 50% would be metastatic even in a known patient with primary cancer. Benign lesions like enchondromas, stress fractures and enostoses would have to be ruled out. Multiple polyostotic uptake of tracer indicates metastatic disease.
A follow-up biopsy would be useful. False negative results are seen with multiple myeloma, lymphoma, leukemia and other associated illnesses. Routine bone scanning may not be necessary. Bone pain may be an indication. When the uptake is diffuse as a in a diffuse metastatic disease, the absence of renal uptake would confirm the ‘superscan’ result (Jacofsky, 2004, p. 24). CT Scan or Computed Tomographic Scan allows good detail of osseous images. Subtle cortical irregularities may be evident. MRI or Magnetic resonance imaging is useful when the bone scan is negative but the patient has symptoms.
MRI is more sensitive than the bone scan for detection of metastases. The extent of involvement of the spinal cord and nerve root compression is best observed in the MRI. Extent of marrow involvement may be determined by MRI before palliative therapy (Jacofsky, 2004, p. 25). PET or Positron Emission Tomography is especially useful in malignancies like thyroid cancer. The fluorodeoxy glucose causes a high sensitivity and specificity. Results of the PET may be positive when all other imaging procedures are negative in thyroid cancer. This modality is being improved.