Mortality in cancer patients with a history of cutaneous squamous cell carcinoma - a nationwide population-based cohort study

We used Danish medical databases, which cover the entire Danish population of 5.6 million inhabitants and linked them using the unique personal identification number assigned to all Danish residents. From 1982 through 2003, we identified 745 index cancer patients with and 79,143 without previous cutaneous SCC. Using Cox proportional hazards regression, we calculated adjusted mortality rate ratios (MRRs) with 95% confidence intervals (CIs).Overall, previous SCC was associated with an increased mortality of cancer (MRR 1.13, 95% CI: 1.04-1.23). When examining index cancers separately, increased MRRs were found for cancer of the lung (MRR 1.23, 95% CI: 1.05-1.43), colon (MRR 1.13, 95% CI: 0.92-1.40), rectum (MRR 1.29, 95% CI: 1.00-1.67), breast (MRR 1.09, 95% CI: 0.82-1.43), and NHL (MRR 1.09, 95% CI: 0.81-1.47), but not for prostate cancer (MRR 0.99, 95% CI: 0.83-1.18).Our results suggest that previous cutaneous SCC is associated with poor prognosis of some cancers. This finding stresses the importance of adherence to the existing recommendations of screening, diagnosis, and treatment of cancer in patients with a history of SCC.Non-melanoma skin cancer (NMSC)--basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) [1]--is associated with an increased risk of developing both subsequent NMSC [2] and other malignancies compared with the general population [3-5]. Common risk factors have been proposed as the cause, for example, ultraviolet radiation (UVR) and immune incompetence [6,7]. In particular, cutaneous SCC is known to be associated with immunosuppression [6,8,9], but whether it is a reliable marker for reduced immune competence that could explain these findings is unknown. Overall, five studies have found higher mortality rates in cancer patients with previous SCC [4,10-13], which also could be explained by reduced immune competence. None of the studies, however, included information on important factors such as cancer treatments and comorbidity. Therefore,