Abstract
IMPORTANCE: Cutaneous squamous cell carcinoma (cSCC) may occur with multiple primary tumors, metastasize, and cause death both in immunocompetent and immunosuppressed patients. OBJECTIVE: To study the rates of second cSCC, metastasis, and death from cSCC in patients with and without organ transplant-associated immunosuppressive treatment. DESIGN, SETTING, AND PARTICIPANTS: This population-based, nationwide cohort study used Cancer Registry of Norway data from 47 992 individuals diagnosed with cSCC at 18 years or older between January 1, 1968, and December 31, 2020. Data were analyzed between November 24, 2021, and November 15, 2022. EXPOSURES: Receipt of a solid organ transplant at Oslo University Hospital between 1968 and 2012 followed by long-term immunosuppressive treatment. MAIN OUTCOMES AND MEASURES: Absolute rates of second cSCC, metastasis, and death from cSCC were calculated per 1000 person-years with 95% CIs. Hazard ratios (HRs) estimated using Cox proportional hazard regression were adjusted for age, sex, and year of first cSCC diagnosis. RESULTS: The study cohort comprised 1208 organ transplant recipients (OTRs) (median age, 66 years [range, 27-89 years]; 882 men [73.0%] and 326 women [27.0%]) and 46 784 non-OTRs (median age, 79 years [range, 18-106 years]; 25 406 men [54.3%] and 21 378 women [45.7%]). The rate of a second cSCC per 1000 person-years was 30.9 (95% CI, 30.2-31.6) in non-OTRs and 250.6 (95% CI, 232.2-270.1) in OTRs, with OTRs having a 4.3-fold increased rate in the adjusted analysis. The metastasis rate per 1000 person-years was 2.8 (95% CI, 2.6-3.0) in non-OTRs and 4.8 (95% CI, 3.4-6.7) in OTRs, with OTRs having a 1.5-fold increased rate in the adjusted analysis. A total of 30 451 deaths were observed, of which 29 895 (98.2%) were from causes other than cSCC. Death from cSCC was observed in 516 non-OTRs (1.1%) and 40 OTRs (3.3%). The rate of death from cSCC per 1000 person-years was 1.7 (95% CI, 1.5-1.8) in non-OTRs and 5.4 (95% CI, 3.9-7.4) in OTRs, with OTRs having a 5.5-fold increased rate in the adjusted analysis. CONCLUSIONS AND RELEVANCE: In this cohort study, OTRs with cSCC had significantly higher rates of second cSCC, metastasis, and death from cSCC than non-OTRs with cSCC, although most patients with cSCC in both groups died from causes other than cSCC. These findings are relevant for the planning of follow-up of patients with cSCC and for skin cancer services.