The only thing worse than a diagnosis of cancer is discovering that the cancer was missed and treatment delayed. For some patients, that delay is the difference between a curable disease and a fatal one. The harm caused by a missed cancer diagnosis is rarely modest, and the medical and emotional consequences for the patient and family are often catastrophic.
This post addresses two questions. First, what are the most common causes of missed or delayed cancer diagnoses in the medico-legal context. Second, what does Ontario law require to prove a cancer misdiagnosis claim, with particular attention to the causation analysis that decides most of these cases.
The scale of the problem
A 2019 study published in the Journal of Healthcare Risk Management, “Missed diagnosis of cancer in primary care: Insights from malpractice claims data,” analyzed 2,155 outpatient diagnostic-error malpractice claims. Missed cancer diagnoses accounted for nearly half of those claims, with lung, colorectal, prostate, and breast cancers leading the list. Roughly three-quarters of the errors involved clinical judgment, most often the failure to order a diagnostic test or the failure to obtain a specialist consult or referral. Eighty-five percent of the errors caused high-severity harm.
Those findings are consistent with the patterns I see in Ontario practice. Cancer misdiagnosis is one of the leading sources of serious malpractice claims in this province. The cancers that most often produce these claims are the ones that most often present with non-specific symptoms in primary care, where the threshold to investigate further is the clinical judgment that goes wrong.
Three patterns of cancer misdiagnosis
Across the cancer misdiagnosis cases I see, the underlying error usually fits one of three categories.
Communication error. A test result identifies a finding that requires follow-up, but the result is not communicated to the patient or to another physician in a timely manner. The patient assumes that no news is good news. The physician’s office assumes someone else is following up. The finding sits in the chart, sometimes for years, until a later test in a different context picks up cancer that has now progressed. Communication errors are often discoverable in the records: there will be a report, a stamp, a sign-off (or its absence), and a clear point at which the system failed.
Investigative error. A patient presents with symptoms or risk factors that should have triggered a cancer-specific investigation, and the investigation is not ordered. This includes failures to refer to specialists, failures to order screening tests at appropriate intervals, and failures to act on family history or other risk factors. A common pattern: a patient with persistent rectal bleeding is treated for hemorrhoids over multiple visits without a referral for colonoscopy, and the colorectal cancer is found only after the disease has progressed.
Interpretation error. The right test is ordered and conducted, but the result is misread. This is common in radiology (a small lung nodule overlooked on a chest X-ray or CT) and in pathology (a malignant lesion called benign on biopsy). Interpretation errors are particularly serious because the patient and the treating physicians have a false sense of security and may not investigate further until much later, when the cancer has advanced.
Where the four common malpractice cancers go wrong
The 2019 study identified lung, colorectal, prostate, and breast cancers as the leading sources of malpractice claims for missed cancer diagnoses. The patterns are consistent in Ontario.
Lung cancer. Frequently a missed nodule on a chest X-ray or CT scan, particularly when the imaging is performed for an unrelated reason and the lung finding is overlooked or noted but not communicated. Smoking history, age, and persistent cough should drive a low threshold to investigate.
Colorectal cancer. Often a delay in referral for colonoscopy in patients with rectal bleeding, anaemia, or a family history of colorectal cancer. Ontario has a structured screening program, ColonCancerCheck, but the screening is only effective when symptomatic patients are referred outside the routine pathway as well.
Prostate cancer. Less commonly the subject of misdiagnosis claims because of the relatively slow progression of most prostate cancers. The cases that do arise tend to involve missed elevations in prostate-specific antigen (PSA), failure to follow up on abnormal digital rectal examination findings, or failure to refer for biopsy.
Breast cancer. Often a misread mammogram, a delay in working up a palpable lump, or a failure to act on a patient’s report of breast changes between screening intervals. Ontario’s Ontario Breast Screening Program covers routine screening; symptomatic presentations require additional clinical judgment.
What proving a cancer misdiagnosis claim requires
The legal framework for a cancer misdiagnosis claim is the same as for any medical malpractice claim. The plaintiff must prove three things:
- The care fell below the standard a reasonable practitioner would have provided in the circumstances (breach of the standard of care)
- The substandard care caused a worse outcome than would have occurred with reasonable care (causation)
- The worse outcome produced compensable harm (damages)
Standard of care is usually the most straightforward element. Communication errors are often clearly documented in the records. Investigative errors require an expert (usually a family physician or specialist) to opine on whether the failure to investigate met the standard of practice at the time. Interpretation errors require an expert in the relevant subspecialty (radiology, pathology, cytology) to review the imaging or specimens and opine on whether the interpretation was reasonable.
Damages, where they exist, are also usually demonstrable. Earlier-stage cancer treatment is generally less aggressive, less morbid, and more likely to result in cure. Later-stage treatment is more aggressive, more morbid, and less likely to result in cure. Where the cancer has been allowed to progress, the additional treatment burden, the deterioration in quality of life, and the loss of life expectancy can be quantified.
The hard element in cancer cases is causation.
The causation challenge in cancer cases
In Canadian medical malpractice law, causation must be proven on a balance of probabilities. The plaintiff has to show that, more likely than not, earlier diagnosis would have produced a better outcome. The Supreme Court of Canada confirmed in Laferriere v Lawson, [1991] 1 SCR 541, a cancer misdiagnosis case, that loss of chance is not generally recoverable in medical negligence. The plaintiff cannot recover simply by showing that the negligence reduced their chance of a good outcome from, say, forty percent to twenty percent. They must show that the better outcome was more likely than not.
This has powerful implications for cancer misdiagnosis cases.
Where a patient’s cancer was, at the time it should have been diagnosed, at a stage with a high cure rate (early-stage colorectal, early-stage breast, early-stage melanoma), and where the delay allowed it to progress to a stage with a poor cure rate, the causation case is often strong. The patient was probably going to live; now they are probably not, or have lost years of life expectancy. That difference is recoverable.
Where the patient’s cancer was already advanced at the time it should have been diagnosed (some pancreatic cancers, some advanced lung cancers, some aggressive lymphomas), the causation case is much harder. If the five-year survival rate at the earliest reasonable point of diagnosis was already below fifty percent, the plaintiff may not be able to show that earlier treatment would more probably than not have produced a better outcome. The claim can fail on causation even where the breach is clear.
The causation analysis in any individual cancer case requires expert evidence from an oncologist. The analytical chain is:
- What stage and grade would the cancer have been at the time it should have been diagnosed?
- What treatment would have been available at that stage?
- What outcome would that treatment more probably than not have produced?
- How does that probable outcome compare with the actual outcome the patient experienced?
Where each step in that chain holds up to expert scrutiny, the case is viable. Where one step is weak, the case will likely not succeed.
Why this matters
For patients and families. A missed or delayed cancer diagnosis is a serious matter. Whether it supports a successful malpractice claim depends, more than anything, on the stage of the cancer at the point it should have been diagnosed and on whether earlier treatment would more probably than not have produced a better outcome. That is an oncologist’s question as much as a lawyer’s question. The first step is to obtain a complete copy of the medical records, including all imaging and pathology, and to seek legal advice from a lawyer experienced in this area. For more on obtaining records under PHIPA, see How to Get Your Medical Records in Ontario.
For families of patients who have died. The estate of a patient who has died from a delayed cancer diagnosis can pursue a malpractice claim on behalf of the estate and family members. The limitations analysis can be complex, particularly where the diagnostic error occurred years before death. Acting promptly, even while the family is still grieving, gives counsel the time needed to assemble the records and obtain expert input before the limitation period runs out.
For prospective claimants generally. The threshold question is whether the case is one where the cancer was at a treatable stage at the point a reasonable practitioner should have diagnosed it. If yes, the claim may be viable. If the cancer was already advanced at the earliest reasonable point of diagnosis, the claim is much more difficult. An honest assessment by experienced counsel, supported by oncology input, will often turn on this analysis.
For more on the threshold considerations in any malpractice claim, see Can I Sue for Medical Malpractice in Ontario? For an overview of the legal process, see Suing for Medical Malpractice in Ontario: What You Need to Know. For the Misdiagnosis practice page, see the linked overview.
The first conversation is free and strictly confidential. The earlier we look at the records, the better.
