Therapy of Colon Carcinoma: An Oncology Perspective
Can J Gastroenterol
Therapy of colon carcinoma: An oncology perspective
Piotr M Czaykowski MSc FRCPC 0
Paul C Adams FRCPC 0
Editor-in-Chief 0
0 Dr Piotr Czaykowski is an Assistant Professor and Medical Oncologist, Department of Medical Oncology and Haematology, CancerCare Manitoba , Winnipeg
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DOncologist, Department of Medical Oncology and
r Piotr Czaykowski is an Assistant Professor and Medical
Haematology, CancerCare Manitoba, Winnipeg.
PA: As gastroenterologists we are often the
physicians that make the diagnosis of colon
cancer…It seems that decisions about
postoperative therapy are based on this assessment. Is
this ideal at the present time?
PC: There is no question that a medical
oncologist’s recommendation regarding the need for
systemic therapy is heavily dependent on the
staging information gleaned in the initial
workup. We look for the following crucial
elements: Is the cancer localized? If localized, is it
rectal or colon cancer? If localized, what is the
status of the parameters that are linked with the
risk of recurrence after surgery? If not localized,
what is the extent of metastatic disease?
Most commonly, the first investigation is an
endoscopic evaluation of the cancer, and
frequently this is performed by a gastroenterologist.
This not only allows for confirmation of
malignancy, but also proves crucial in helping medical
and radiation oncologists determine the need for
radiotherapy in distal large bowel tumours.
Although the definition of where the rectum ends and the
sigmoid begins remains controversial, clinical trials commonly
define the rectum as being the distal 12 cm to 15 cm of the large
bowel, 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
endoscopic report that says rectal cancer (without any measurement),
an operative note that calls the tumor rectosigmoid, and a
computed tomography scan that calls it sigmoid. Because we only use
radiotherapy routinely for rectal cancers, this question of location
becomes an important one – so an explicit statement by the
endoscopist of the location of the tumour is of great consequence.
It is also helpful in advanced cancers to have some indication of
the patency of the lumen.
Even in this day and age, a surprising number of patients
undergo a primary bowel resection without adequate staging.
This leads to some unnecessary surprises, and occasionally leads
to poor intraoperative choices. There appears to be an emerging
consensus that patients with extensive metastatic disease with
relatively asymptomatic primary tumours are probably best served
by commencing chemotherapy as soon as possible, and worrying
about the primary tumour later, if symptoms necessitate (
1
).
Thus, the key staging investigations, often initiated by the
gastroenterologist, ideally should be done before resection of the
primary tumour, and should include chest imaging and a computed
tomography scan of the abdomen and pelvis. A preoperative
carcinoembryonic antigen test (CEA) is helpful, primarily as a
prognostic indicator (
2
). Because I am focusing on colon cancer, I will
not address the role of magnetic resonance
imaging and endoscopic ultrasound in staging
rectal cancer.
When the patient does undergo surgery,
generally for apparently localized disease, it is
important that the surgeon confirm that there
are no obvious metastases (and reports on this),
and that he or she focuses on harvesting an
adequate number of lymph nodes. It has been
recognized for some time that insufficient nodal
sampling leads to under-staging; the exact
number of nodes necessary for accurate nodal staging
remains controversial but many centres use 12 as
the magic number. Clearly, finding an adequate
number of nodes depends to some extent on the
surgeon, but it is also heavily reliant on the
pathology team. Even if positive nodes are
identified, it appears to be important to remove as
many as possible, because there are now some
data that suggest the number and ratio of
positive nodes are also important in prognosis (
3,4
).
Currently, there are no recommendations
for the routine use of positron emission tomography scanning
in apparently localized colon cancer. Those centres that have
ready access most commonly use this modality for trying to
determine if a patient with metastatic disease can be
considered for resection of the metastases with curative intent.
Similarly, the use of other tumour markers (for example CA
19-9) and the use of molecular profiling (eg, looking for
microsatellite instability or for overexpression of vascular
endothelial growth factor or epidermal growth factor) remains
the domain of clinical trials for the most part.
A problem across most of Canada is that there are often
excessive delays in getting the patient through the whole process of
diagnosis and treatment. In a recent review of 93 Manitoba
patients with stage III colon cancer who received adjuvant
chemotherapy, we (...truncated)