Missed Diagnosis or Misdiagnosis: How to Proceed with a Medical Malpractice Claim Involving Cancer Treatment

Written By: Bryan Sansom and Danika Winkel, Summer Student

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According to the Canadian Cancer Society, cancer is the leading cause of death in Canada, responsible for approximately 30% of all deaths.[1]  Unfortunately, some cancer related deaths arise out of a missed or late diagnosis which effectively delays treatment and allows unrestrained progression of the disease.

Meeting the burden of proving causation in medical negligence cases can be difficult given the complicated nature of diseases such as cancer which can be difficult to diagnose and are typically progressive.  Furthermore, it is difficult to determine how early diagnosis and intervention would have changed the patient’s outcome.

One of the risks in cancer is a missed diagnosis which, at best, leads to a delayed diagnosis. This means treatment is delayed which can then lead to a worse outcome than if the diagnosis was made sooner.

Lawsuits alleging a delayed diagnosis are often defended by the “loss of a chance” argument.  This argument is premised on the idea that the most the plaintiff can prove in court is the loss of a chance at a better prognosis. The defendant will often argue that it is not actually possible to predict whether the cancer patient would have been better off with an earlier diagnosis and earlier treatment.

In a lawsuit for delayed cancer diagnosis, the plaintiff must prove on a balance of probabilities that the delay caused or contributed to the unfavourable outcome.  In Cottrelle v Gerrard,[2] the Ontario Court of Appeal held that “[i]t is not sufficient to prove that adequate diagnosis and treatment would have afforded a chance of avoiding the unfavourable outcome unless that chance surpasses the threshold of ‘more likely than not’.”

Consequently, in order to prove causation, the plaintiff must show the following.

First, the plaintiff must show that they likely had cancer at the time of the alleged substandard care. This is a potentially difficult hurdle as there is likely no objective evidence of the cancer at the time of the substandard care (e.g., if the proper diagnostic tests been utilized the diagnosis likely would have been made).

Second, the plaintiff must also show that they would have been diagnosed in a timely fashion but for the substandard care. This will be easier to prove as many hospitals and clinics have a battery of tests and diagnostic tools that can efficiently and expeditiously facilitate a diagnosis.

Third, the plaintiff must show that they likely would have received timely treatment. This will also depend on the type and nature of the cancer, the stage of progression, and the various treatment options available to the plaintiff in the circumstances.

Finally, the plaintiff must show that timely treatment would likely have led to a better outcome. Expert opinions, clinical trials and other data relating to cancer treatment outcomes can assist in this regard.

Personal injury lawyers can help you navigate these complicated legal claims. If you or a loved hurt as a result of medical negligence, the lawyers at McLeish Orlando LLP will help you understand your options decide whether a lawsuit is appropriate in the circumstances.

[1] Cancer Statistics At a Glance – Canadian Cancer Society

[2] 178 OAC 142, 67 OR (3d) 737 [2003].

Alexis Perlman


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