Aim: Colorectal cancer (CRC) is a major cause of cancer death in New Zealand. Incidence and mortality rates are regularly reported but more detailed information concerning the epidemiology of the disease is not readily available. The aim of this study is to describe the epidemiology of colorectal cancer, with particular reference to gender; subsite distribution; stage at diagnosis; tumour grade; the contribution of recognisable aetiological factors; and the resection rate and type of surgery performed for rectal cancer.
Methods: All 2272 pathology reports of colorectal cancer submitted to the National Cancer Registry for the year 2000 were reviewed and restaged according to the classical Dukes system. Age, gender, stage, subsite distribution, differentiation, tumour type, associated pathology and type of rectal cancer specimen were recorded.
Results: The gender ratio for all cases was equal. One third of resected cancers were in the rectum, one third in the left colon and one third were proximal to the splenic flexure. Men had more rectal cancer (M:F 1.6:1) and women more colon cancer (0.9:1). Right-sided cancers were of significantly higher grade than left-sided cancers. The proportion of right-sided cancers increased with advancing age in both men and women. Three per cent of patients had synchronous tumours and 0.2% of patients had phenotypic features of familial adenomatous polyposis (FAP). Fourteen per cent of patients were Dukes stage A at diagnosis, 43% stage B and 43% stage C. Rectal cancers were more likely to be stage A than colon cancers (odds ratio 1.6). Stage and grade of CRC were significantly associated. Ninety one per cent of cancers were resected; 29% of patients with rectal cancer had an abdominoperineal resection and 6% a local excision.
Conclusions: The current stage distribution of CRC is in keeping with a predominantly unscreened population. The subsite distribution of cancer and its relationship to age and gender are similar to other high-risk countries; however, its relationship to grade of tumour has not previously been reported. An abdominoperineal resection rate of 29% reflects the mix of specialised colorectal and general surgical units treating rectal cancer in New Zealand and is in line with or better than recent overseas data that reflect national or regional practice.