Nationwide study of cancer risk among hip replacement patients in Sweden

Background. Orthopedic implants and their fixatives contain materials with carcinogenic potential. Whether these implants are linked to subsequent can cer development remains unknown, mainly because large-scale, long-term foll ow-up data are scarce. Methods: We conducted a nationwide cohort study in S weden to examine cancer incidence among 116 727 patients who underwent hip replacement surgery during the period from 1965 through 1994. Through recor d linkage to the Swedish Cancer Register, we identified all incident cancer s through 1995 in this population (693 954 person-years of observation). Fo r each cancer type, the observed number of cases was divided by that expect ed in the general Swedish population to produce standardized incidence rati os (SIRs). Results: Relative to the general population, the cohort had no o verall cancer excess (SIR = 1.01; 95% confidence interval [CI] = 0.99 to 1. 03). However, we observed elevated SIRs for prostate cancer (SIR = 1.16; 95 % CI = 1.11 to 1.22) and melanoma (SIR = 1.15; 95% CI = 1.01 to 1.30) and a reduction in stomach cancer risk (SIR = 0.83; 95% CI = 0.75 to 0.92). Long -term follow-up (greater than or equal to 15 years) revealed an excess of m ultiple myeloma (SIR = 1.86; 95% CI = 1.01 to 3.11) and a statistically non significant increase in bladder cancer (SIR = 1.42; 95% CI = 0.98 to 1.99). There was no material increase in risk for bone or connective tissue cance r for either men or women in any follow-up period. Conclusions: In this, th e largest study to date, hip implant patients had similar rates of most typ es of cancer to those in the general population. Although the excesses of m elanoma, multiple myeloma, and prostate and bladder cancers may be due to c hance, confounding, or detection bias and should be interpreted cautiously, they warrant further investigation because of the ever-increasing use of h ip implants at younger ages.