“You have cancer.” Those are perhaps some of the scariest words a patient can ever hear. Probably the most common question a patient askes, after “can it be treated?” is “could it have been prevented?”

Delayed diagnosis of cancer can give rise to medical malpractice claims

According to the Canadian Cancer Society about 2 in 5 Canadians will develop cancer and 1 in 4 Canadians will die of cancer. The 5 year survival rate for cancer is 63% but that varies greatly depending on the type of cancer. However, generally speaking, the earlier you are diagnosed, the better your chances of surviving.

So if there are unreasonable delays in diagnosing a patient’s cancer, there may be grounds for a medical malpractice claim. However, these types of malpractice claims face a number of hurdles that malpractice lawyer, and their clients, need to be aware of.

No “loss of chance” in Canada

In the United States, if a plaintiff can show that a doctors delayed diagnosis reduced their chance of successful treatment by , say, 10% then the plaintiff’s remedy may be assessed at 10% of their potential future losses.

Not so in Canada. It is not enough for a medical malpractice plaintiff to show a loss of chance of early treatment or better outcome. Instead, the plaintiff must show on a balance of probabilities (more likely than not) that they would not have suffered the harm or loss if they had been diagnosed earlier.

As one can imagine, this can be a daunting challenge but there are ways that causation can be proved in cancer misdiagnosis cases and damages awarded.

This article will review the options that plaintiffs and their counsel have available to overcome the burden of proof and briefly explore relevant case law that provides those tools.


Any cancer misdiagnosis claim begins with an examination of the medical and legal issues of causation. In other words, can the plaintiff prove:

  1. The cancer was present;
  2. The patient would have been diagnosed at an earlier time if the doctor had met the standard of care; and
  3. that the outcome of their disease probably would have been more favourable.

In other words, it isn’t enough to show that an earlier diagnosis may have increased the chances of successful treatment or survival. The plaintiff must prove that an earlier diagnosis probably would have changed the outcome.

As the Supreme Court of Canada declared in Snell v Farrell, scientific precision is not required for causation. Furthermore, circumstantial evidence can lead to an inference of causation in cancer cases by the trier of fact.


Once an initial diagnosis for cancer has been made, oncologists classify the cancer into various “stages” to determine the extent to which the disease has progressed.

The universal staging for many cancers is called the TNM system, which considers the tumour’s size, whether there has been any local lymph node involvement and if there is evidence that the cancer has spread (metastasized) to other parts of the body. There are four stages of cancer under this system (I-IV). Often, comparison of the stages of cancer can assist in proving legal causation.


Typically, cancer is treated by removing the tumorous mass, along with treating any remaining cells through various forms of therapy (for example, chemotherapy or radiation). Cancer is considered medically “cured” if a person is free of cancer cells for a period of five years.

Statistically, the earlier the diagnosis (the earlier the cancer is identified and treated), the better the chances for recovery and a “cure”.

How are cancer claims defended?

Defence counsel usually argues that an earlier diagnosis would not have resulted in survival.

“It was already there”: A common defence is that the plaintiff’s cancer was already growing and an earlier diagnosis would not have changed the patient’s outcome. Defence counsel will use growth models, based on the so-called “doubling time” theory, to predict the inception date of the cancer in the patient and argue that the cancer was already in advanced stages at the time of the defendant’s negligence.

The flaw in this argument is that growth models are based on the presumption that cancer has a predictable rate of growth. Rate growth models use mathematical formulas to predict the time it will take for the volume or mass of cancer to double, and then work backwards to determine the inception date – the date at which the cancer appeared.

There are limitations to growth rate models:

  • They are based on studies of limited populations;
  • They assume constant growth and ignore variability in growth rates between patients and within patients; and
  • They are not proper comparators for assuming growth because they are based on measurements taken in different circumstances under different conditions.

“You were going to die anyway”: The other common defence argument in cancer misdiagnosis claims is that the biology of the disease makes it inevitable that a plaintiff was going to die from the cancer, regardless of any delays in diagnosis. The argument is based on the idea that a delay will only cause a loss of chance for a better outcome, rather than the better outcome the law requires. This would mean that the plaintiff is not entitled to recoverable damages.

The flaw in this defence is that it runs counter to the basic principles of common law that if a defendant has caused the plaintiff harm, the plaintiff is entitled to recovery compensation for that harm.

Other Considerations

Canadian courts have consistently confirmed that the burden of proof in medical malpractice claims remains on the plaintiff.

The Supreme Court of Canada has rejected lower court rulings that a plaintiff’s inability to produce evidence to prove causation mandated that a court must find causation.

However, the courts have ruled that an adverse inference of causation may be established when two criteria are met:

  • The defendant’s negligence must have undermined the plaintiff’s ability to prove causation; and
  • The plaintiff can produce at least some evidence of causation.

Statistics important evidence

Courts will permit the use of studies and statistics to fill in evidentiary gaps and medical studies may be used in these situations to draw adverse inferences.

For example, in its 2016 decision in Benhaim v St-Germain, the  Supreme Court of Canada was faced with the issue of whether a lack of early testing can create a barrier to proving causation that would warrant a rebuttable inference of causation, or an adverse inference of causation. The court found that “an adverse inference of causation may discharge the plaintiff’s burden of proving causation”. The court added that the decision to draw such an inference must be based on “an evaluation of all of the evidence”.