Causation and the Role of Expert Evidence in Medical Malpractice Litigation: Hacopian-Armen Estate v Mahmoud, 2021 ONCA 545

Written By: Brandon Pedersen & Aidan Vining, Student-at-Law

Causation and the Role of Expert Evidence in Medical Malpractice Litigation: Hacopian-Armen Estate v Mahmoud, 2021 ONCA 545

Factual Background of the Case

A recent case from the Ontario Court of Appeal demonstrates the integral role experts play in medical malpractice litigation. In Hacopian-Armen Estate v Mahmoud, 2021 ONCA 545, a gynecologist was found to have negligently caused the death of his patient.

Ms. Hacopian-Armen died in 2011 from Stage IV uterine leiomyosarcoma (“uLMS”), an aggressive form of cancer that originates in the muscular outer layer of the uterus. Diagnosing uLMS is difficult as it has features similar to fibroids, which are fairly common benign, non-cancerous growths. Fibroids cannot be distinguished from uLMS by imaging. Instead, uLMS can be discovered by conducting an endometrial biopsy – a short and simple in-office procedure.

Ms. Hacopian-Armen’s health issues began when she was diagnosed with fibroids in 1999. In 2009, she was referred to the gynecologist for treatment.

Ms. Hacopian-Armen exhibited several risk factors for diseases of the uterus at her first meeting with the gynecologist in 2009. The risk factors included: being over 40 years old, experiencing abnormal uterine bleeding, and never having given birth. The gynecologist conducted a routine swab of Ms. Hacopian-Armen but did not perform an endometrial biopsy.

Unfortunately, Ms. Hacopian-Armen’s symptoms worsened. In April 2011, the gynecologist performed an endometrial biopsy, which revealed that Ms. Hacopian-Armen had a Stage IV cancerous tumour in her uterus. Ms. Hacopian-Armen had a hysterectomy and began chemotherapy, but it was too late. Ms. Hacopian-Armen died in August 2011, four months after the gynecologist discovered the cancerous tumour.

Ms. Hacopian-Armen’s family started a lawsuit against the gynecologist. They alleged that his failure to conduct an endometrial biopsy was negligent, in that conducting said procedure would have likely detected Ms. Hacopian-Armen’s cancer at a much earlier stage, making it likely that her death would have been prevented.

Trial Decision

Expert witnesses played a significant role in the trial decision.

The trial judge accepted Ms. Hacopian-Armen’s expert’s opinion that Ms. Hacopian-Armen likely had the cancerous uLMS at the first meeting with the gynecologist, and that had an endometrial biopsy been performed on that date, the uLMS likely would have been detected. The trial judge also found that the Ms. Hacopian-Armen’s prognosis would have been substantially improved if the uLMS had been found and treated in 2009. The cancer could have been removed from her body at that time before it had a chance to spread. The trial judge concluded that but for the gynecologist’s failure to perform the biopsy in 2009, Ms. Hacopian-Armen would probably not have died of Stage IV uLMS. The risk of uLMS was real, and it was foreseeable that if uLMS went untreated, it would likely result in serious injury or death.

Ultimately, the trial judge concluded that:

  • The gynecologist breached the standard of care that he owed to Ms. Hacopian-Armen by failing to perform an endometrial biopsy;
  • A biopsy performed at the first appointment in 2009 would have detected the uLMS, which would have greatly improved Ms. Hacopian-Armen’s prognosis; and
  • The harm that occurred to Ms. Hacopian-Armen and her family members was foreseeable and caused by the gynecologist’s failure to perform the biopsy.

Justice Brown summarized her conclusion as follows:

[156] Based on all of the evidence adduced at trial, including the medical records, the opinions and testimony of the medical experts adduced on behalf of both parties, the submissions of counsel and the case law, I find that Dr. Haider Mahmoud fell below the standard of care by failing to perform an endometrial biopsy on May 25, 2009. His notetaking fell below the standard expected of a reasonably skilled specialist in his professional field.  Further, in failing to perform an endometrial biopsy on May 25, 2009, this allowed the plaintiff’s LMS to progress to the point that the course of the disease was unable to be altered by the time it was finally diagnosed. It was foreseeable, and not too remote, that the negligence would result in the plaintiff’s final loss. I am satisfied that causation, both factual and legal, have been established.

Appellate Decision

The gynecologist challenged the trial decision based on alleged errors in the trial judge’s conclusions on legal and factual causation.

Legal Causation

The gynecologist argued that the trial judge relied on retrospective reasoning and the benefit of hindsight in determining causation. It was argued that the trial judge erred by asking whether it was foreseeable that the presence of uLMS, if untreated, would lead to serious injury or harm. Rather, the gynecologist argued that the proper questions to be asked were whether it was foreseeable to a reasonable gynecologist that (a) Ms. Hacopian-Armen had uLMS in 2009; (b) an endometrial biopsy would have diagnosed the uLMS; and (c) not performing an endometrial biopsy could lead to a delayed diagnosis of uLMS. This is because, the gynecologist argued, uLMS is a rare form of cancer and the harm was too remote and unforeseeable.

The gynecologist argued that the trial judge’s retrospective approach to causation would create a dangerous precedent and force physicians to order unnecessary tests to avoid the risk of missing unforeseeable diseases.

The unanimous panel at the Court of Appeal agreed that the trial judge inappropriately blended her factual and legal analysis with hindsight. However, the Court held that it did not matter that the gynecologist did not know that Ms. Hacopian-Armen had uLMS in 2009. What mattered was the combination of risk factors being presented by Ms. Hacopian-Armen at the time. Due to her age, the fact that she had not had a child, and the symptoms she was having, an endometrial biopsy was required and it was reasonably foreseeable that the failure to conduct one would preclude detection of uterine diseases which would cause serious harm if left untreated.

The Court stated that it is sufficient that the harm suffered is of a kind, type or class that was reasonably foreseeable as a result of the gynecologist’s negligence. By failing to conduct a biopsy that would have detected cancers of the same class or kind as uLMS (including uLMS itself), it was foreseeable that uLMS or other cancers of that kind would go undetected, resulting in injury to Ms. Hacopian-Armen.

The Court also rejected the argument that this case would result in doctors ordering unneeded tests. In this case, due to Ms. Hacopian-Armen’ symptoms and risk factors, a biopsy was actually necessary and ought to have been performed by a competent gynecologist.

The Court therefore rejected this ground of the gynecologist’s appeal and upheld legal causation.

Factual Causation

The gynecologist also argued that the judge erred in finding that but for his negligence, the injury would not have occurred. Specifically, the gynecologist argued that the trial judge erred in (a) finding that uLMS was likely present at the first meeting in 2009, and (b) in finding that an endometrial biopsy would have likely detected uLMS in 2009.

The Court determined that the standard of review applicable to this case was one of palpable and overriding error, as negligence matters involve questions of mixed law and fact. The trial judge’s treatment of expert evidence was therefore given deference.

The trial judge explicitly found Ms. Hacopian-Armen’s experts to be more reliable than those of the gynecologist. Two experts testified on behalf of Ms. Hacopian-Armen that uLMS was likely present in 2009 when Ms. Hacopian-Armen was first examined by the gynecologist. The trial judge accepted this evidence and rejected the gynecologist expert’s opinion that there was no proof of uLMS being present in 2009. The Court of Appeal found no error with the trial judge’s acceptance and rejection of expert evidence.

The Court of Appeal also found no error with the trial judge’s acceptance of Ms. Hacopian-Armen’s expert opinion that uLMS likely would have been detected had a biopsy been conducted in 2009. When there are conflicting expert opinions presented by the parties, a trial judge is entitled to accept one side’s expert opinion over the other. The trial judge found Ms. Hacopian-Armen’s experts to be “forthright, impartial and consistent” whereas the gynecologist’s experts were described as “less than forthright” and “argumentative.” The trial judge found Ms. Hacopian-Armen’s experts to be more credible and thus accepted their evidence over the gynecologist’s experts.


The appeal was ultimately dismissed, and the trial judge’s finding of liability on the gynecologist was upheld.

Why This Matters

This case demonstrates the significant role experts play in medical malpractice litigation. Due to the technical and complex nature of these cases, judges rely heavily on expert evidence to inform their opinion and ultimate decision of a case. For this reason, it is important that you obtain an experienced personal injury lawyer that is familiar with dealing with experts and complicated cases. Obtaining the right expert for your case and obtaining the best evidence from that expert can be the difference between winning and losing a case.

If you or a loved one have been injured, please contact McLeish Orlando Lawyers LLP.

Alexis Perlman


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