Screening and diagnosis

Colorectal cancer is the most prevalent cancer in Singapore with more than 1000 patients diagnosed each year¹. Current recommendations² suggest screening of asymptomatic individuals aged 50 years and above with yearly faecal occult blood testing (FOBT). This was performed in the past with the guaic-based FOBT which gives a qualitative result and requires dietary restriction.

The recent introduction of an immunochemical quantitative FOBT kit (OC-light, Eiken) that detects specific human haemoglobin or haem within the stool allows for measurement of the amount of blood in the stool and obviates the need for any dietary restrictions prior to the test.

Currently, Japan already has a mass-screening programme since 1992, using this quantitative FOBT for screening nearly 5 million people per year. The incidence of colorectal cancer in this population with FOBT positive results is between 0.15-0.2%.³ We have already begun using this new quantitative test on a routine basis in our department.

Initial evaluation showed that 6.6% of patients were FOBT positive with a cut-off level of more than 100ng/ml⁴. This new FOBT test kit had a 94.4% sensitivity in detecting pathology. The cancer detection rate was 11.1% and polyp detection rate was 22.2%. Positive FOBT results and subsequent evaluation with colonoscopy also allowed other conditions to be picked-up early, such as diverticular disease, inflammatory bowel disease and haemorrhoids.

Furthermore, polypectomy at the time of endoscopy will also lower the risk of developing subsequent colorectal cancer. We suspect that this new quantitative test will eventually be the test of choice to detect faecal occult blood.

Another recent development is that of virtual colonoscopy or computed tomographic (CT) colonography. This involves the use of an advanced multidetector spiral CT scanner to generate 2D and 3D images of the colon and rectum, as well as other abdominal and pelvic organs. It is non-invasive and a major advantage is its ability to detect unsuspected diseases outside of the colon, something that is not possible with endoscopy or barium enema. However, if there is a mucosal lesion detected in the colon, the patient will still need to undergo colonoscopy and biopsy.

Laparoscopic colorectal resections

Laparoscopic colorectal resection is gaining popularity since its introduction more than 10 years ago. The new frontier is no longer in resections for benign disease but in using laparoscopy for cancer resections and in particular laparoscopic total mesorectal excisions (TME) in rectal cancers.

Laparoscopic resection for colonic cancers has been compared to conventional midline laparotomies in 3 large-scale studies in Europe, the Unites States and United Kingdom (UK). All three showed an equivalent rate of lymph node harvesting and cancer clearance compared with the open technique, but with the added advantage of shorter hospital stay and reduced wound pain inherent to the laparoscopic approach.

The CLASICC trial (UK)⁵ , however, showed that laparoscopic rectal resections were associated with increased incidence of nerve damage and increased risk of circumferential margin involvement. The results of this study may, however, be confounded by the wide spectrum of experience in laparoscopy across multiple centres. We have undertaken many colorectal resections laparoscopically with good results and will be publishing our results in due course.

Since Heald⁶ reported on the advantages of total mesorectal resections, it has now been adopted as the standard of care for low rectal tumours. This involves removing all the mesorectum and anastomosing the descending colon to the anus in an ultralow anterior resection.

The new frontier is in performing this demanding operation laparoscopically. We have performed seven laparoscopic TME for low rectal tumours in our unit with good results thus far and will be striving to develop our expertise in this area in the future.

Polyposis registry

The Singapore Polyposis Registry was set up in 1989 and based at the Department of Colorectal Surgery, Singapore General Hospital. It was recognised by the Ministry of Health in 1990 as a national registry and has been instrumental in promoting awareness of Familial Adenomatous Polyposis (FAP) and Hereditary Non-Polyposis Colorectal Cancer (HNPCC).

Currently, there are 82 families with FAP and 92 families with HNPCC on follow-up. Genetic counselling and screening of relatives of affected probands have helped to reduce the incidence of colorectal cancer in these genetically predisposed patients.

FAP is inherited in an autosomal dominant fashion and every member of a FAP family has a 50% chance of being a FAP carrier. With a virtually 100% risk of cancer in FAP patients, it is imperative to select this high-risk group for annual endoscopic surveillance from their teens.

Identification can now be performed even before FAP carriers develop polyps in their colon by means of a blood test. This is the Protein Truncation Test, performed at our Colorectal Cancer Research Laboratory. It has a sensitivity of 75-80% and a specificity of 100% when correlated with colonoscopy findings. This presymptomatic genetic test for FAP removes the need for repeated colonoscopic surveillance in those who test negative.

In those who test positive, it increases compliance to repeated clinical surveillance and better timed prophylactic colectomies that will undoubtedly lead to decreased patient morbidity and mortality.

Laparoscopic vs open anterior resection

A/Prof Eu Kong Weng, Head and Senior Consultant
Dr Kam Ming Hian, Associate Consultant
Department of Colorectal Surgery
Singapore General Hospital

References

1.	A Seow, WP Koh, KS Chia, LM Shi, HP Lee, K Shanmugaratnam. Trends in cancer incidence in Singapore 1968-2002. Singapore Cancer Registry Report No. 6.
2.	MOH Clinical Practice Guidelines 2/2004.
3.	Saito H. Screening for colorectal cancer: current status in Japan. Dis Colon Rectum 2000 Oct; 43(10 Suppl): 578-84.
4.	Lim YK, Tang CL, Ooi BS, Ho KS, Lim JF, Eu KW. Initial experience in colorectal cancer screening using quantitative immunochemical faecal occult blood test (FOBT) in Singapore. (in print)
5.	Guillou PJ, Quirke P, Thorpe H, Walker J, Jayne DG, Smith AM, Heath RM, Brown JM; MRC CLASICC trial group. Short-term end-points of conventional versus laparoscopic-assisted surgery in patients with colorectal cancer (MRC CLASICC trial): multicentre randomised controlled trial. Lancet 2005; 365: 1718-26.
6.	Heald RJ, Husband EM, Ryall RD. The mesorectum in rectal cancer surgery – the clue to pelvic recurrence? Br J Surg 1982 Oct; 69(10): 613-6.