Dr. Lillian Siu


A clinical trial is a research study that tests new ways to prevent, detect or treat cancer. Our aim is to test new therapies to improve outcomes for patients and to determine if the new treatment is superior to the standard of care. Other trials focus on preventing and diagnosing the disease. Princess Margaret Cancer Centre also conducts supportive care clinical trials to explore ways to improve quality of life for cancer patients.

The Princess Margaret has one of the world's largest and most highly skilled cancer clinical trials programs. With 700 active clinical trials and more than 200 investigators, The Princess Margaret is leading the way in drug discovery and research.

The traditional model of drug development follows a stepwise approach from Phase 1 to Phase 2 to Phase 3 trials. Some newer study designs are also being used, including: seamless clinical trials (that go from Phase 1 to 2 to 3 within one large study often involving hundreds to thousands of patients), basket studies (matching a new drug to different cancer types that share the same genomic abnormality or mutation) and umbrella studies (which match different new drugs to different genomic mutations within one cancer type).

“For every new drug we need to understand how safe and effective it is and whether it can replace the standard of care.”

– Dr. Lillian Siu, Co-Director, Tumour Immunotherapy Program, Director of Phase 1 Clinical Trials Program

Types of Clinical Trials
  • Drug Trials
  • Radiation Trials
  • Surgical Trials
  • Medical Device Trials
  • Combination Trials (i.e. radiation + drugs)
  • Adoptive Cell Therapy Trials (i.e. CAR T-cells)
  • Trials that explore quality of life and symptom control
SAFETY: Our Top Priority

Participating in a clinical trial allows a patient to access drugs or therapies that are not part of a standard course of treatment.

“People who participate in the trials are the heroes who help develop new drugs and treatments for the future,” says Susanna Sellmann, who oversees operations in the Cancer Clinical Research Unit (CCRU).

There are also risks. Trials adhere to regulatory guidelines before they start and our cancer experts review patient safety throughout every step of a trial. Our quality assurance group performs reviews on trials and all research protocols are reviewed by a Research Ethics Board at University Health Network (UHN) or through Clinical Trials Ontario.


It is essential patients understand they are participating in a research study that is completely voluntary and they can withdraw at any time, without affecting their future relationship with care providers.


Patients must have a doctor's referral and meet required criteria.


Clinical trials have both known and unknown potential risks. Side effects from treatment are possible. That is why frequent testing and monitoring are necessary, along with doctor visits.

  • What are the risks and benefits?
  • Are there additional tests or visits required?
  • What is the time commitment required?
  • What is the length of the trial?
  • How will health information be kept private?
  • What are the alternative treatments?

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