Incidence, prevalence and distribution of bone metastases

Abstract

Metastatic bone disease is the most common malignant bone lesion seen in adults. It is the third most common metastatic site after the lung and liver (Abrams, et al., 1950). Bone metastases usually become apparent after the diagnosis of the primary tumour has been established, but in up to 22.6% of patients bone metastases are the first lesion to be detected (Conroy, et al., 1988). Whereas clinical examination, routine imaging and laboratory tests, allow rapid determination of the primary tumour in the majority, the origin of the skeletal metastasis remains unknown in about 30% of cases (Wilson, et al., 1981). The incidence and prevalence of bone metastases is difficult to determine with accuracy. The data are derived from three types of study: necropsy series, bone scintigram series and hospital data banks, and estimates show a marked variance (Galasko, 1986). At post-mortem the prevalence of bone metastases for all cancers ranges from 7 to 27% and is similar for both men and women (Copeland, 1964). The most frequent primary cancer associated with skeletal metastases in women is breast cancer and prostatic cancer in men (Table I). Bone metastases are rare in children. The rates from necropsy studies may be overestimated since patients dying in hospital with terminal metastatic disease are an unrepresentative sample. On the other hand, the rates may be underestimated since examination of the skeleton at postmortem is both difficult and time-consuming. In most series, pathologists have limited bone samples to specific locations most commonly affected by the metastatic process such as the vertebrae, pelvis, ribs or those areas found to be abnormal at previous radiography. Higher rates of bone involvement have been found in scintigraphic surveys. In one study of 1,143 patients with a nonosseous primary tumour, bone scintigraphy was abnormal in 61% of patients. Two-thirds of these patients had a primary tumour originating from breast, lung or prostate, and of these tumours there were abnormal scintigrams in more than 60% of cases (Tofe, et al., 1975). In contrast to necropsy series and clinical experience, a positive rate of approximately 50% was also seen for cola-rectal and uterine cancers (Bonnheim, et al., 1986). Bone scintigraphy is the most sensitive diagnostic test for detecting bone metastases. With conventional radiography a change of 30-50% in bone density is required before bone metastases may be identified, whereas a change of 5-10% is sufficient when using bone scintigraphy (Citrin. et al., 1977). However, false negative scans may occur when the lesion is less than 2-3 mm in diameter, is rapidly growing, or is entirely osteolytic rarely seen in metastases from solid tumours (Goris et al., 1985). Moreover bone scan abnormalities are not specific, and several benign conditions (necrosis, infections, arthritis, fractures, Paget’s disease) give rise to false-positive results. The false-positive rate is particularly high when there is only one scintigraphic abnormality.