In August 2024, Paul Cahill settled a medical malpractice claim on behalf of a woman in her 60s whose colorectal cancer diagnosis was delayed by approximately three years. The patient had had a normal colonoscopy at the start of the relevant period. In the years that followed, she developed persistent rectal bleeding and abdominal discomfort. She reported these symptoms to her family physician. She also reminded the family physician of her family history of colon cancer. Despite the combination of symptoms and family history, no further diagnostic testing was ordered and no specialist referral was made. Three years passed. When the patient was eventually referred for a repeat colonoscopy, the procedure revealed advanced colon cancer with large lesions. Subsequent staging investigations confirmed advanced disease. Treatment required chemotherapy, radiation therapy, and multiple surgeries. The case settled before trial. The terms are confidential.
This case is doctrinally useful as an illustration of two recurring themes in primary-care medical malpractice litigation. The first is the role of family history in calibrating the standard of care: a patient with a known family history of a serious disease is owed a different level of vigilance than a patient with no such history. The second is the cost of reassurance from a single prior negative test: a “normal colonoscopy” three years ago is not a guarantee that nothing has developed in the interim, particularly where new symptoms emerge in a patient at elevated baseline risk. The combination of new symptoms and a known family history of the same disease should prompt action, not deferral.
The clinical context
Colorectal cancer is one of the most common cancers in Canada and one of the leading causes of cancer death. The Canadian Cancer Society’s published surveillance data places colorectal cancer among the top three cancers in both incidence and mortality for both men and women. The disease has a substantially better prognosis when diagnosed at an early stage. Five-year survival is in the 90 percent range for Stage I disease, falls to roughly 70 to 80 percent for Stage II, drops to 50 to 70 percent for Stage III, and falls to approximately 10 to 15 percent for Stage IV (metastatic) disease. These figures are consensus oncological statistics drawn from Canadian Cancer Society reporting and the Ontario cancer registry; they reflect the general population and should not be applied to any particular patient without qualification.
The diagnostic system in Ontario for colorectal cancer is built on two tracks: population-level screening for average-risk patients and clinical investigation for symptomatic or high-risk patients.
The screening track operates through Ontario Health’s ColonCancerCheck program. At the time of the events giving rise to this claim, the program offered a fecal immunochemical test (FIT) every two years from age 50 to 74 to average-risk patients. The FIT detects occult blood in the stool, and a positive result triggers a follow-up colonoscopy within eight weeks. For people considered at increased risk because of family history (one or more first-degree relatives diagnosed with colorectal cancer), the program recommended colonoscopy rather than FIT, starting at age 50 or ten years before the age of diagnosis of the youngest affected relative, whichever was earlier. Patients with hereditary syndromes (Lynch syndrome, familial adenomatous polyposis) follow a separate, more intensive surveillance pathway through the High Risk Ontario Breast Screening Program’s equivalent for colorectal cancer.
In May 2026, Ontario announced revisions to ColonCancerCheck effective July 2026. The average-risk FIT starting age is being lowered from 50 to 45, and the family-history pathways are being recalibrated: patients with a first-degree relative diagnosed under age 60 are eligible for colonoscopy starting at age 40 or ten years before the age of diagnosis (whichever is earlier), with a five-year interval, while patients with a first-degree relative diagnosed at age 60 or over move to FIT every two years starting at age 45 (rather than colonoscopy). These changes are being phased in. The historical structure (FIT from 50 for average risk, colonoscopy from 50 or 10 years earlier for first-degree family history) was the structure in place at the time of the events in this case and is the structure against which the standard of care for the relevant period would be assessed.
The screening program is the appropriate diagnostic pathway for asymptomatic patients regardless of which structure is in force.
The clinical investigation track operates separately and is the appropriate pathway for symptomatic patients regardless of screening status. The published guidance, including the Canadian Association of Gastroenterology guidelines and the various Cancer Care Ontario clinical pathways, identifies a set of “red flag” symptoms that warrant prompt investigation rather than reliance on the screening schedule. These red flag symptoms include rectal bleeding, change in bowel habits, unintentional weight loss, persistent abdominal pain, iron deficiency anemia, and a palpable abdominal mass. The presence of any of these symptoms in an adult patient generally triggers a workup that begins with a clinical assessment by the family physician and proceeds, in most cases, to colonoscopy by a gastroenterologist or general surgeon.
A particularly important clinical concept in the present case is the interval cancer: a colorectal cancer diagnosed in the period between a negative screening colonoscopy and the next scheduled screening interval. Interval cancers are a recognized clinical phenomenon. They can arise from lesions that were present but missed at the prior colonoscopy (because of incomplete bowel preparation, technical difficulty visualizing certain colon segments, or operator dependence), from polyps that were incompletely removed, or from rapidly growing tumours that develop de novo between examinations. The published gastroenterology literature on interval cancers identifies the rate at roughly three to nine percent of colorectal cancers diagnosed in screened populations, depending on the definition and the screening interval. The clinical implication is that a normal colonoscopy is not a guarantee that the patient is cancer-free for the full screening interval. A patient who develops symptoms in the period between scheduled colonoscopies requires evaluation as a symptomatic patient, not reassurance based on the prior normal study.
The patient and the breach
The patient was a woman in her 60s. Several years before the relevant events, she had undergone a colonoscopy that was reported as normal. She had a known family history of colon cancer. Her family physician was aware of this history.
In the years following the normal colonoscopy, she developed symptoms. The symptoms included persistent rectal bleeding (bloody stools) and abdominal discomfort. She reported both to her family physician. Her family physician was also reminded of the family history of colon cancer at the relevant time.
The family physician did not order further diagnostic testing. The family physician did not refer the patient to a gastroenterologist or general surgeon for repeat colonoscopy. The family physician did not order a FIT, a CT colonography, or any other investigation that might have identified the developing cancer. The patient continued under the care of the family physician with no investigation of the symptoms for approximately three years.
When the patient was eventually referred for a repeat colonoscopy, the procedure revealed advanced colorectal cancer with large lesions. Subsequent staging investigations confirmed the advanced nature of the disease. The treatment required was correspondingly intensive: chemotherapy, radiation therapy, and multiple surgeries.
The standard of care for primary-care evaluation of rectal bleeding
The standard of care for primary-care evaluation of rectal bleeding is a matter on which expert evidence from a Canadian family physician of equivalent training and experience is required in litigation. Description here is general background and should not be taken as a substitute for that evidence in any particular case. With that caveat, the general consensus in Canadian family practice can be sketched.
Rectal bleeding in an adult patient is a recognized red flag symptom. The family physician’s task on encountering rectal bleeding includes a clinical assessment (a focused history, a physical examination including abdominal examination and digital rectal examination, and consideration of the patient’s risk factors), and a decision about further investigation. For a patient under 50 with mild bleeding consistent with a benign anorectal cause and no other concerning features, conservative management with a defined plan for follow-up if symptoms persist may be appropriate. For a patient over 50, or for a patient with a family history of colorectal cancer, or for a patient whose bleeding persists despite empirical treatment for benign causes, the threshold for further investigation is substantially lower. The published Cancer Care Ontario clinical pathways and the various Canadian gastroenterology guidelines support the proposition that a patient over 50 with persistent rectal bleeding and a family history of colorectal cancer should be referred for colonoscopy without delay.
The family history element is doctrinally significant. A first-degree family history of colorectal cancer roughly doubles a patient’s baseline lifetime risk. Multiple first-degree relatives with the disease, or relatives diagnosed at a young age, raise the risk further. A family physician aware of a patient’s family history of colorectal cancer is not in a position to attribute new GI symptoms to a benign cause without investigation; the family history is a clinical fact that elevates the index of suspicion and lowers the threshold for referral. The published guidance on screening for high-risk patients recognizes this by recommending colonoscopy rather than FIT for first-degree relatives of colorectal cancer patients. The same principle that drives the screening pathway applies to the diagnostic pathway: where the patient has known elevated risk, the workup of symptoms should reflect that risk.
The three-year period of unexplained symptoms in this case, in a patient with a known family history of colorectal cancer, fell outside the general consensus on the standard of care. The expert evidence at trial would have identified the specific points at which the family physician’s response fell short and would have addressed whether earlier referral would have produced an earlier diagnosis and a different treatment trajectory.
The legal framework
A medical malpractice claim arising from a delayed colorectal cancer diagnosis in Ontario is analyzed under the four elements of the standard negligence framework: duty of care, breach of the standard of care, damages, and causation.
Duty of care. The duty of care owed by a family physician to a patient in an ongoing primary-care relationship extends to the investigation of new symptoms, the maintenance of awareness of the patient’s risk factors (including family history), and the timely referral for specialist assessment when the clinical picture requires it. This element is not typically contested in cases of this type.
Standard of care. The standard of care was discussed in the preceding section. The expert evidence would have addressed the specific question of whether a reasonable Canadian family physician of equivalent training and experience would have ordered further investigation or referred for colonoscopy at the point when the patient first reported the combination of symptoms and family history. The expert evidence would also have addressed whether the continuation of the patient’s care over the three-year period without investigation fell below the standard.
Damages. The damages in this case were substantial, even without a death claim. The treatment burden imposed by an advanced colorectal cancer diagnosis (chemotherapy, radiation therapy, and multiple surgeries) is significant. The recovery from extensive abdominal surgery in a patient in her 60s carries its own consequences. The risk of recurrence after treatment for advanced disease is elevated relative to early-stage disease; the published five-year survival data described above is reflected in the prognosis the patient was given at the time of diagnosis. The economic losses include the past and future medical costs, the past and future losses of income or housekeeping capacity, the costs of future care needs as the patient ages with the consequences of her treatment, and pain and suffering. The case was a non-fatal claim, so there were no Family Law Act dependency claims of the type that would have applied in a wrongful-death case, but the damages remained meaningful.
Causation. The causation analysis in a delayed-cancer-diagnosis case where the patient survives but with a more advanced cancer at diagnosis than would have been the case with timely investigation is doctrinally interesting. The plaintiff is not establishing that the patient would have lived but for the breach (because the patient is alive). The plaintiff is establishing, on the balance of probabilities, that the patient would have had a different disease course but for the breach. The different disease course typically involves an earlier stage at diagnosis, a less intensive treatment regimen, a lower recurrence risk, a better five-year prognosis, and reduced pain and suffering.
The framework remains the “but for” test from Clements v Clements, 2012 SCC 32. The Supreme Court of Canada’s dicta in Laferrière v Lawson, [1991] 1 SCR 541, on the use of statistical evidence (the court is not paralyzed by statistical abstraction) and on the rejection of loss of chance as a compensable theory remain controlling. The Ontario Court of Appeal’s reasoning in Hacopian-Armen Estate v Mahmoud, 2021 ONCA 545, on the “same class or kind” foreseeability analysis and on the limits of the Goodwin v Olupona evidentiary-gap principle, applies in the delayed-colorectal-cancer-diagnosis context as it does in the delayed-uterine-cancer-diagnosis context.
The plaintiff’s case on causation would have rested on expert oncological evidence that the cancer was likely at an earlier stage at the time the family physician first encountered the symptoms, that timely investigation would have produced an earlier diagnosis, and that the earlier diagnosis would have permitted a less intensive treatment regimen with a better prognosis. The defence position would have explored whether each step in the counterfactual could be established on the balance of probabilities, drawing on the same kinds of statistical and clinical considerations that are familiar from cancer-misdiagnosis litigation generally.
The resolution
The matter resolved by settlement in August 2024. The settlement was reached before trial. The terms are confidential. The settlement reflects both parties’ assessment of the strengths and weaknesses of the standard-of-care, causation, and damages evidence, weighed against the risks and costs of trial.
Why this matters
For patients with a known family history of colorectal cancer, the lesson is that family history is a clinical fact that matters across the patient’s lifetime, not just at the time of an initial intake. A family physician who is aware of a family history of colorectal cancer at intake should remain aware of it when new GI symptoms emerge years later. The patient is entitled to expect that the family history will be taken into account in the workup of those symptoms. If the workup proceeds as if the patient were at average risk, the patient should ask whether the family history has been factored in. A second opinion is appropriate where it has not.
For patients who have had a normal colonoscopy and subsequently develop concerning symptoms, the lesson is that the normal colonoscopy does not foreclose investigation. The published gastroenterology literature recognizes interval cancers as a real clinical phenomenon. Symptoms that develop between scheduled colonoscopies require evaluation as new symptoms, not reassurance based on the prior normal result. Red flag symptoms (persistent rectal bleeding, change in bowel habits, weight loss, persistent abdominal pain, iron deficiency anemia) warrant prompt investigation regardless of how recently the prior colonoscopy was performed.
For family physicians, the case illustrates two related risks. The first is the risk of anchoring on a prior negative test. A normal colonoscopy three years ago does not establish that current symptoms have a benign cause; the symptoms still need to be evaluated on their merits. The second is the risk of underweighting family history once it has been recorded. A family history of cancer at intake does not become less relevant over time; if anything, it becomes more relevant as the patient enters the age range in which the family member was diagnosed.
For the broader practice of medical malpractice litigation in Ontario, the case joins the cancer-misdiagnosis sub-cluster in the notable-cases library. Other entries include the trial victory in Hacopian-Armen v Mahmoud (uterine leiomyosarcoma, where the breach was a failure to perform an endometrial biopsy), the appeal in the same matter (where the Court of Appeal clarified the foreseeability analysis), the hepatitis B liver cancer surveillance settlement (where the breach was a long-term surveillance failure in a known high-risk patient), and the delayed breast cancer diagnosis settlement (where the breach was a missed opportunity to investigate in a young symptomatic patient). The four cases together illustrate the recurring patterns of cancer-misdiagnosis litigation in Ontario: failure to perform an indicated diagnostic test (Hacopian-Armen), failure to maintain a surveillance schedule for a known high-risk patient (hepatitis B), failure to investigate symptoms in a younger patient (breast cancer), and failure to integrate family history into the workup of new symptoms (this case). For a more general overview, the firm’s blog post on common causes of cancer misdiagnosis is a useful starting point.
For prospective clients who have experienced a delayed colorectal cancer diagnosis, the threshold question is whether the diagnostic system functioned as it should have given the patient’s risk profile. The records of the primary-care visits, the imaging and laboratory reports, the referral history, and the timing of investigations are the starting points. The two-year limitation period in Ontario runs from the date the patient knew or ought to have known that the delayed diagnosis was the result of an act or omission of the defendant.
Settlement Date: August 2024
Settlement Type: Confidential settlement before trial
Defendant: Family physician (not named)
Counsel for the plaintiff: Paul J. Cahill
