Second primary cancers in patients with colorectal cancer after a curative resection

Background: Colorectal cancer (CRC) patients have a risk of developing other malignancies. Understanding the characteristics of the second primary cancers is important to establish an effective follow-up system. Methods: This study investigated 301 CRC patients to assess the risk factors for postoperative primary cancers arising from organs distinct from the colorectal area (extracolorectal cancers). The observed/expected ratio (O/E ratio) was calculated using the Osaka Cancer Registry, to determine the rate of increase of extracolorectal cancers. Results: The frequency of postoperative extracolorectal cancers was 12.6%. A logistic regression analysis showed only age to be an independent risk factor for postoperative extracolorectal cancer development. The O/E ratio of overall postoperative extracolorectal cancer was significantly higher than one (O/E ratio 2.6, P<0.01). In each organ, the frequency of lung and gastric cancers were significantly higher than one with O/E ratios of 3.2 (P<0.01) and 2.7 (P<0.05). Conclusions: The frequency of postoperative extracolorectal cancers in CRC patients was significantly higher than that in the normal population, especially for lung and gastric cancers. Clinicians should carefully follow patients for a possible recurrence of CRC and educate CRC patients with regard to the high risk of second primary cancers. © 2011 The Japanese Society of Gastroenterological Surgery.