Nonmelanoma skin cancers and risk of subsequent malignancies: a cancer registry-based study in Bulgaria.

Analysis of new primary tumors following nonmelanoma skin cancers (NMSC) has a public health and risk assessment interest, as well as potential implications for etiologic inference. The aim of this study is to evaluate the risk of the second primary tumors occurrence after NMSC development. A cohort of 2620 cases (1335 males and 1285 females) with nonmelanoma skin cancers registered in Bulgarian National Cancer Registry in 1993 was examined. The follow-up period represented a total of 15,856 person-years at risk. Over this period 128 (83 in men, 45 in women) new secondary tumors were established. After NMSC appearance, both genders show higher risk for the second primary tumors occurrence. This risk is greater for men. For both sexes after NMSC development there is increased risk for occurrence of second primary cancers of head and neck, thyroid, lung, larynx, bladder, colon, as well as cutaneous malignant melanoma, non-Hodgkin's lymphoma and leukemias. The results of considering only basal cell carcinomas show an elevated risk in patients of both sexes for appearance of second primary tumors of head and neck, bladder, larynx, lung and colon as well as non-Hodgkin's lymphoma and cutaneous malignant melanoma. The results of considering only squamous cell carcinomas show an increased risk in persons of both sexes for development of second primary cancers of head and neck, skin, thyroid, lung, stomach, as well as leukemias, non-Hodgkin's lymphoma and cutaneous malignant melanoma. The association between NMSC and subsequent increased risk for appearance of second primary skin and visceral tumors determine the necessity of monitoring the patients with NMSC.