Abstract
Second cancer is a new cancer that occurs in someone who had a history of cancer. The incidence of cancer is on the increase in the global scene. This phenomenon constitutes huge health problems especially with comorbidity effects with other health conditions which have made the diagnosis and treatment of cancer patients a complex issue. This study determined the comorbidity of second cancer based on a retrospective study of 474 patients that received care and who were first treated of cancer, and after one year developed another cancer or cancer-free. The results revealed that the incidence of second cancer was approximately 39.5% and 41.4% of the patients had one or more other diseases (s) had second cancer. Adjusted and unadjusted odds ratio from logistic regression showed patients with a history of smoking were 3.58 more likely to develop second cancer when no adjustment was made to the model while the risk increased after adjustment. Furthermore, patients who are diagnosed with other diseases are 1.56 more likely to develop second cancer than cancer patients without other diseases. Based on the area under the characteristics curve, logistic regression effectively distinguished between the two groups of patients considered. This study reveals the significant influences of comorbidity and smoking on the incidence of second cancer. Therefore, it could be used to formulate policies on controlling tobacco smoking and to create health awareness on the effect of a clinical factor on second cancer and other health conditions within the study area and its environs.

Key words: Sensitivity; Specificity; Odd Ratio; Comorbidity; Cancer; Nigeria.