Incidence and pattern of second primary cancer in patients diagnosed with primary cancer

The long survival of patients with primary cancer increases the chance of such patients developing second primary cancer (SPC). The development of SPC in cancer survivors exerts a large psychological, social and economic burden on patients and their families. The aim of the present study was to assess the risk of cancer survivors developing SPC. The study included patients who had been diagnosed with a first primary cancer in five organs (stomach, colorectum, lung, breast and thyroid), which are the five most common sites of cancer in patients from Korea, at the regional cancer center in Jeonbuk National University Hospital between January 2007 and December 2009. The standardized incidence ratio (SIR) of SPC according to sex and site was calculated from 5,209 patients who were followed up to September 2017. General incidence was acquired from the National Cancer Registry of Republic of Korea. SPC occurred in 6.2% (323/5,209) of patients, and the incidence of SPC among the five major types of cancer was in the order of breast (8.8%, 46/524), colorectum (8.6%, 86/1,003), gastric (6.6%, 89/1,358), thyroid (4.7%, 67/1,437) and lung cancer (3.9%, 35/887). When all SPC sites were included, the SIRs of SPC in patients with colorectal cancer and breast cancer were >1.0 (1.21 and 1.66, respectively). Breast cancer and thyroid cancer exhibited a high site relationship (P<0.05), and colorectal cancer had a high site relationship with gastric cancer (P<0.05). The present study analyzed the incidence and pattern of SPC in patients with cancer who were diagnosed with primary carcinoma in five organs. The results of the study may be useful for effective follow-up and early detection of SPC in patients with cancer.