Organ transplant recipients are at increased risk of a wide range of malignancies, especially cutaneous squamous cell carcinomas (SCC). Few previous population-based studies have quantified and compared cancer risks according to graft type and with long-term follow-up. Using nationwide Swedish registers, we identified 10,476 recipients transplanted from 1970 to 2008 and followed them for cancer occurrence. Relative risks of cancer in comparison with the general population were expressed as standardized incidence ratios (SIR) and within the transplanted cohort as incidence rate ratios (IRR). During a total follow-up of 93,432 person-years, patients were diagnosed with 1,175 cancers excluding SCC, and with 2,231 SCC, SIR(cancer excl SCC) 2.4 (95% CI, 2.2-2.5); SIR(SCC) 121 (95% CI, 116-127). Cancer risks were most increased among heart and/or lung recipients SIR(cancer excl SCC) 3.3 (95% CI, 2.8-4.0); SIR(SCC) 198 (95% CI, 174-224), followed by kidney SIR(cancer excl SCC) 2.3 (95% CI, 2.1-2.4); SIR(SCC) 121 (95% CI, 116-127) and liver recipients SIR(cancer excl SCC) 2.3 (95% CI, 1.9-2.8); SIR(SCC) 32 (95% CI, 24-42). During follow-up, risk of cancer excluding SCC remained stable while risk of SCC tripled over 20 years irrespective of graft type, partly due to a subgroup of patients developing new SCCs at a rapidly increasing rate. In summary, post-transplant cancer risk varied by transplanted organ and by cancer site, with the bulk of the excess risk driven by an exceptionally high and accelerating risk of SCC. These findings underscore the importance of regular skin screening in organ transplant recipients.
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