Therapy of Colon Carcinoma: An Oncology Perspective

Abstract

r Piotr Czaykowski is an Assistant Professor and MedicalOncologist, Department of Medical Oncology andHaematology, CancerCare Manitoba, Winnipeg.PA: As gastroenterologists we are often thephysicians that make the diagnosis of coloncancer…It seems that decisions about postop-erative therapy are based on this assessment. Isthis ideal at the present time?PC:There is no question that a medical oncolo-gist’s recommendation regarding the need for sys-temic therapy is heavily dependent on thestaging information gleaned in the initialworkup. We look for the following crucial ele-ments: Is the cancer localized? If localized, is itrectal or colon cancer? If localized, what is thestatus of the parameters that are linked with therisk of recurrence after surgery? If not localized,what is the extent of metastatic disease?Most commonly, the first investigation is anendoscopic evaluation of the cancer, and fre-quently this is performed by a gastroenterologist.This not only allows for confirmation of malig-nancy, but also proves crucial in helping medicaland radiation oncologists determine the need forradiotherapy in distal large bowel tumours.Although the definition of where the rectum ends and the sig-moid begins remains controversial, clinical trials commonlydefine the rectum as being the distal 12 cm to 15 cm of the largebowel, and most of us use that as our day-to-day reference point.If I start cursing in clinic, it is usually because I have an endo-scopic report that says rectal cancer (without any measurement),an operative note that calls the tumor rectosigmoid, and a com-puted tomography scan that calls it sigmoid. Because we only useradiotherapy routinely for rectal cancers, this question of locationbecomes an important one – so an explicit statement by theendoscopist of the location of the tumour is of great consequence.It is also helpful in advanced cancers to have some indication ofthe patency of the lumen.Even in this day and age, a surprising number of patientsundergo a primary bowel resection without adequate staging.This leads to some unnecessary surprises, and occasionally leadsto poor intraoperative choices. There appears to be an emergingconsensus that patients with extensive metastatic disease withrelatively asymptomatic primary tumours are probably best servedby commencing chemotherapy as soon as possible, and worryingabout the primary tumour later, if symptoms necessitate (1).Thus, the key staging investigations, often initiated by the gas-troenterologist, ideally should be done before resection of the pri-mary tumour, and should include chest imaging and a computedtomography scan of the abdomen and pelvis. A preoperative car-cinoembryonic antigen test (CEA) is helpful, primarily as a prog-nostic indicator (2). Because I am focusing on colon cancer, I willnot address the role of magnetic resonanceimaging and endoscopic ultrasound in stagingrectal cancer.When the patient does undergo surgery, gen-erally for apparently localized disease, it isimportant that the surgeon confirm that thereare no obvious metastases (and reports on this),and that he or she focuses on harvesting an ade-quate number of lymph nodes. It has been rec-ognized for some time that insufficient nodalsampling leads to under-staging; the exact num-ber of nodes necessary for accurate nodal stagingremains controversial but many centres use 12 asthe magic number. Clearly, finding an adequatenumber of nodes depends to some extent on thesurgeon, but it is also heavily reliant on thepathology team. Even if positive nodes are iden-tified, it appears to be important to remove asmany as possible, because there are now somedata that suggest the number and ratio of posi-tive nodes are also important in prognosis (3,4).Currently, there are no recommendationsfor the routine use of positron emission tomography scanningin apparently localized colon cancer. Those centres that haveready access most commonly use this modality for trying todetermine if a patient with metastatic disease can be consid-ered for resection of the metastases with curative intent.Similarly, the use of other tumour markers (for example CA19-9) and the use of molecular profiling (eg, looking formicrosatellite instability or for overexpression of vascularendothelial growth factor or epidermal growth factor) remainsthe domain of clinical trials for the most part.A problem across most of Canada is that there are often exces-sive delays in getting the patient through the whole process ofdiagnosis and treatment. In a recent review of 93 Manitobapatients with stage III colon cancer who received adjuvantchemotherapy, we found that of the 58 identified as having coloncancer before surgery, the median time from diagnosis to surgerywas 24 days, with 40% of patients waiting more than four weeks.After surgery, the median wait to start adjuvant chemotherapywas 55 days, with approximately one-third of this time reflectinga delay in referral to medical oncology.PA:Can you update us on the optimal oncology treatments forcolon cancer in Canada?PC: Although there are some minor variations amongprovinces, most seem to adhere to very similar standards. Because