Incidence Differences Between First Primary Cancers and Second Primary Cancers Following Skin Squamous Cell Carcinoma as Etiological Clues.

The incidence ranking of SPCs after skin cancers largely follows the incidence ranking of FPCs indicating that overall skin SCC does not greatly interfere with the intrinsic carcinogenic process. The main deviations in incidence between FPC and SPC appeared to be due to shared risk factors or immunological processes promoting immune responsive cancer types.