Second primary colorectal cancer in the era of prevalent screening and imaging

BackgroundOncology literature is increasingly recognizing prevalence of second primary cancers including several longitudinal studies showing an increased risk of colorectal cancer following a prostate cancer diagnosis. A retrospective study was conducted to examine the relationship between prior prostate cancer diagnoses and subsequent colorectal cancer diagnoses. MethodsA multi-centre prospective colorectal cancer registry was queried for patients with a prior history of prostate, breast or lung cancer. Characteristics of these patients were compared to patients with colorectal cancer and no prior cancer history. ResultsOf 4660 cases of colorectal cancer diagnosed between 1998 and 2011, 2665 (57.2%) were male, median age was 68 years. For patients with a history of prostate cancer (n = 111), breast cancer (n = 61) and lung cancer (n = 23), the great majority of subsequent colorectal cancer diagnoses occurred in the initial 2 to 4 years after the first cancer diagnosis. This was accompanied by an increased rate of asymptomatic colorectal cancer at presentation, due to both screen detected and incidental cancer diagnoses. There was no clear relationship between any prostate cancer treatment and subsequent colorectal cancer risk, location or timing. DiscussionIn the modern era, there is an increased rate of colorectal cancer diagnosis in years shortly following another common cancer history. This is consistently seen across different primary tumour streams including prostate, breast and lung cancers and in part contributed by screen detected and incidental colorectal cancer diagnoses. Future studies should consider this potential confounding factor when asserting an increased rate of colorectal cancer as a second primary cancer.