Colorectal cancers usually metastasise to the liver, lung or central lymph nodes. If detected preoperatively, the disease at these distant sites may be potentially resected during surgery for the primary tumour as part of a synchronous resection. It may also be resected at subsequent surgeries as part of an interval or staged approach.
Patients with early colorectal cancers often do not have any symptoms. This highlights the importance of colorectal screening (which is discussed below) to detect these tumours in their early stages where treatment has a much better success rate. Symptoms of colorectal cancer may vary depending on the location of the tumour. Rectal tumours may present with fresh per-rectal bleeding, tenesmus or passage of per-rectal mucus. Left sided tumours may cause a change in bowel habit (constipation/diarrhoea), change in stool-calibre, per-rectal bleeding and abdominal bloatedness. Patients with right-sided tumours may present with iron-deficiency anaemia.
If the colorectal cancer obstructs, this would lead to features of intestinal obstruction such as gross abdominal distension, obstipation and vomiting. Abdominal pain in this setting may be a sign of impending perforation especially when there is a closed loop obstruction arising as a result of a competent ileocaecal valve. If the cancer perforates, this would lead to signs of generalised peritonitis in the case of free perforation, or signs of sepsis and localised tenderness in the case of a localised sealed perforation. Colorectal cancers seldom present with massive per-rectal bleeding. In cases of advanced colorectal cancer, the patients may experience anorexia, weight-loss, cachexia and systemic symptoms depending on the site(s) of distant metastases.
Approach to management
A general approach to a patient suspected of having colorectal cancer would initially centre on investigations aimed at confirming or refuting the diagnosis of colorectal cancer. This is usually achieved by doing a colonoscopy. If a tumour is seen, this would be biopsied to obtain histological confirmation of the diagnosis. A complete colonoscopy would also be important to exclude other synchronous tumours which can occur in almost 4% of patients diagnosed with colorectal cancer.2 Having confirmed the diagnosis of colorectal cancer, the next step would be to stage the cancer preoperatively by doing a computerised tomography (CT) scan. This would assess the local extent of the tumour, including its size, and more importantly, whether it has invaded into the adjacent structures and organs, and whether there are any local complications such as a sealed perforation. The scan would also assess the extent of regional and distant disease by looking for evidence of regional lymphadenopathy or tumour deposits in other organs such as the liver or lungs. In the case of low rectal cancers below the level of the peritoneal reflection, the local extent is better assessed by a separate magnetic resonance imaging (MRI) scan or endoscopic rectal ultrasound scan. Such detailed preoperative investigations would allow optimal planning and individual tailoring of the patients’ subsequent treatment. A preoperative carcinoembryonic antigen (CEA) level should be obtained as a baseline to facilitate a more meaningful postoperative CEA level surveillance.
The management of colorectal cancer is best achieved by a multidisciplinary approach involving oncologists, radiologists, pathologists, gastroenterologists and surgeons. Advances in radiotherapy, chemotherapy and targeted immunotherapy have greatly contributed to the treatment of colorectal cancer in the adjuvant and neoadjuvant settings. However, surgery with strict attention to operative technique and oncological principles, have remained the primary curative modality for this cancer. Technical and technological advances have also permitted an increasingly minimally-invasive surgical approach to remove the cancer. Compared to a decade ago, laparoscopic colorectal surgery is now often routinely offered to patients with colorectal cancer in its earlier stages. More recently, robotic-assisted surgery have also facilitated resection of low rectal cancers where the increased manoeuvrability of the robot aids the surgeon in dissecting the tumour within the narrow confines of the pelvis, especially in males. Open surgery still has a place in treating larger, more locally-advanced colorectal tumours, as well as obstructed tumours where gross bowel dilatation precludes minimally invasive approaches.
Whether a colorectal tumour is removed via a minimally invasive method or an open surgery, the principles of surgical resection remains the same. At any point where minimally invasive surgery would compromise such principles, an open approach should be adopted instead. Surgical oncological principles centre on achieving complete resection of the primary tumour with clear surgical margins. This involves dissection along embryological planes and en-bloc removal of any organ or structures that may be invaded by the primary tumour, such as the urinary tract, adjacent bowel and the abdominal wall. Another hallmark of oncological resection is the en-bloc removal of the regional lymph nodes draining the tumour. This is achieved by dividing the surgical specimen at the origin of the primary vessel supplying the portion of the colorectum in which the tumour is located. After surgical removal, the apical lymph nodes should be tagged for identification by the pathologist and a minimum of 12 lymph nodes should be examined. Historically, patients with distant metastatic disease had been considered incurable and subjected to palliative treatment due to the poor prognosis in this group of individuals. More recently, with the advent of improved surgical techniques, better perioperative care and advance in adjuvant therapies, patients who had previously been considered incurable are now being considered for more aggressive surgical and adjuvant therapy with an intention to achieve cure. Colorectal cancers usually metastasise to the liver, lung or central lymph nodes. If detected preoperatively, the disease at these distant sites may be potentially resected during surgery for the primary tumour as part of a synchronous resection. It may also be resected at subsequent surgeries as part of an interval or staged approach. Following surgical resection of the tumour, the specimen would be carefully examined and staged by the pathologist. This would enable subsequent stratification of these patients to help decide the necessity for subsequent adjuvant therapy. Following treatment, these patients require close clinical follow-up to enable any disease recurrence or metachronous tumours to be detected and treated early to maximise outcome. Most surveillance protocols span a minimum of 5 years. The optimal surveillance regime is still controversial, but the recommended surveillance protocols by the various major task force groups share important similarities and principles of surveillance [Table 1].3 For most surgeons in Singapore, postoperative surveillance would consist of regular monitoring of the CEA, CT scans, as well as colonoscopy.
Any patients with suspicious symptoms should undergo colonoscopy, and these cases are not considered under screening. Screening applies to asymptomatic individuals who would otherwise not have sought any form of medical attention. Most colorectal cancers are adenocarcinomas and many of these cancers arise via the adenoma-carcinoma pathway where a small sub-centimetre polyp progresses through a series of changes that brings it from an early adenoma to a late adenoma, and finally developing into a cancer. This process may take approximately ten years. This long pre-malignant period makes this an ideal cancer for screening, where detection and removal of adenomatous polyps may prevent colorectal cancer and reduce mortality. The Ministry of Health Clinical Practice Guidelines (2010) summarises colorectal cancer screening in Singapore. The guidelines divide individuals into 3 groups [Table 2]: average-risk, increased-risk and very high-risk individuals.
Average-risk individuals are asymptomatic individuals without any family history of colorectal cancer. For this group, screening should begin from the age of 50 years. The two screening modalities of choice in this group would include colonoscopy or faecal occult blood testing. Faecal testing may utilise the traditional Guaiac-based tests or the more specific and sensitive faecal immunochemical test (FIT). If chosen, faecal testing should be done annually and if positive, the patient should undergo colonoscopy. Colonoscopy is the current gold standard in colorectal evaluation, and it is both diagnostic as well as therapeutic when utilised to remove polyps. When an average-risk individual above the age of 50 has a normal colonoscopy, the next test may be done within 10 years provided the patient remains asymptomatic. Increased-risk individuals are those with a family history of colorectal cancer or polyps, especially if they are first-degree relatives who were diagnosed below the age of 60 years or if there are more than one first degree relative. These individuals should undergo 5-yearly colonoscopies from the age of 40 years or 10 years younger than the youngest affected family member. Increased-risk individuals also include those who have a personal history of polyps. These patients should undergo colonoscopy within 3 to 5 years depending on whether they had low-risk (e.g. single subcentimetre tubular adenoma with low-grade dysplasia) or high-risk polyps (e.g. multiple polyps, more than 1cm, villous, high-grade dysplasia). Very high-risk individuals are those with familial adenomatous polyposis (FAP) syndrome, hereditary non-polyposis colorectal cancer (HNPCC) syndrome and inflammatory bowel disease (IBD). These individuals require frequent endoscopic evaluation from an earlier age. Faecal testing is not applicable for increased-risk and very high-risk groups, where colonoscopy is recommended. The use of CEA as a mode of colorectal screening is also not recommended due to its low sensitivity and specificity in this respect. Although a raised CEA detected during regular health screening may prompt investigations which may detect a colorectal cancer, a normal preoperative CEA level is quite commonly found even in patients with colorectal cancer. Hence, a normal CEA level at general health screening may lead to a false sense of security with respect to colorectal cancer. In summary, colorectal cancer is the most common cancer in Singapore. In its early stages, it may not cause any symptoms. Therefore, colorectal cancer screening aims to detect patients with this disease in its early stages where treatment has a much higher success rate. Furthermore, the removal of precancerous polyps during colonoscopic screening can prevent the future progression to cancer. Hence, it is hoped that with increased public awareness of the disease, more can be done to improve the outcome and survival of our patients.
1 National Registry of Diseases. Trends in cancer incidencein Singapore 2010-2014. Singapore Cancer Registry Interim Report. Singapore Cancer Registry.
2 Prevalence and prognosis of synchronous colorectal cancer: a Dutch population-based study. Mulder SA, Kranse R, Damhuis RA, etal. Cancer Epidemiol. 2011 Oct; 35(5):442-7
3 The Role of Postoperative Surveillance in Colorectal Cancer. Hammond K, Margolin DA. Clin Colon Rectal Surg. 2007 Aug; 20(3): 249-54 Clinical Oncology.
This article was first published in the Dec 2016 edition of MG Singapore Magazine. For more information on colon health, you can make an appointment with Dr Kevin Kaity Sng, head over to GetDoc.
by Hridya Anand
A biochemist by education who could never put what she studied to good use, finally found GetDoc as a medium to do what she loved - bring information to people using a forum that is dedicated to all things medical. View all articles by Hridya Anand.