CANCER RISK FROM ORTHOPEDIC PROSTHESES

Permanent replacement of joints damaged by fracture or arthritis has b ecome common over the last 50 years. Vigilance over possible long-term adverse effects of metal prostheses is required. Some of the metal co mponents are potentially carcinogenic. Prolonged contact of metal allo ys with body fluids results in gradual corrosion of even the most iner t metals. Three cohost studies of persons with a hip prosthesis have b een reported; they provide direct, quantitative observations of cancer risk in a human population with hip prosthesis. The design and the re sults of these studies are similar. Combining the results sharpens the precision of risk estimates. Collectively, the studies examined cance r risk in 40,945 patients followed up for a mean 8.5 years after hip r eplacement. Overall, the relative risk of cancer was 1.02 (95 percent CI 1.00 to 1.05). There was an 8 percent excess of haemopoietic malign ancy (leukaemia and lymphoma), with a total of 347 cases observed (RR 1.08, 95 percent CI 0.97 to 1.20). Significant deficits of cancers of the breast and large bowel were seen in the two smaller studies, but c ombined results from all three studies suggest the relative risk is cl ose to unity. Cancer risk in the first 10 years after hip replacement was not different from that expected, but there was an excess of borde rline statistical significance 10 or more years after surgery, with a relative risk of 1.08 (95 percent CI 1.00 to 1.13) based on 1,005 case s. All three studies were well-designed and executed. Their results ar e not alarming, but give no cause for complacency, since the number of patients with a prosthesis and the length of time they live with the prosthesis will increase. A register of malignancy complicating joint prosthesis would not help quantify any risk. Instead, a large cohort s tudy of patients with joint prostheses is needed, including informatio n on the type and composition of the prosthesis and on potential confo unding exposures for each patient. Measures of corrosion in cancer cas es and of tissue levels of relevant metal ions in cases and controls ( prosthesis but no cancer) matched for age, sex, and time since inserti on would be valuable. Such a study could be done internationally, usin g orthopedic units with good clinical records for 10 to 15 years in ar eas with long-term cancer registration.