How and why more than 1,000 people received diluted chemotherapy will be the focus of a third-party investigation in Ontario.

Ontario Premier Kathleen Wynne announced the investigation Thursday in Toronto as 1,176 people in her province and in New Brunswick were told they had received diluted chemotherapy, leaving them worried, angry and searching for answers.

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Ontario Premier Kathleen Wynne, left, and Health Minister Deb Matthews announced an independent third-party investigation into chemotherapy errors on Thursday while touring a breast cancer research centre. (Frank Gunn/Canadian Press)

"[Ontario Health Minister Deb Matthews] is pulling together all of the people who are necessary to figure out what happened, to get to the bottom of it, to understand how this happened and whether there's something systematic that needs to be addressed," Wynne told a news conference at the official opening  the Louise Temerty Breast Cancer Centre at the Sunnybrook Health Sciences Centre in Toronto.

Matthews acknowledged there are also questions about whether privatization of chemotherapy preparation played any role.

In a letter released to reporters, Matthews said her office became aware of the underdosing on March 30.

Cancer Care Ontario doesn't have a count of how many hospitals mix chemotherapy themselves or outsource the service, said Dr. Carol Sawka, an oncologist and vice-president of clinical programs and quality initiatives at the agency.

Whenever patients systematically receive more or less chemotherapy than prescribed it's of concern, said Dr. Tony Fields, a professor of medical oncology at the University of Alberta in Edmonton.

Fields supports the Institute of Safe Medications Canada's call for a national standard to clearly label overfill — the source of the overdilution issue.

Commercially available IV bags often include an excess volume of saline solution that pharmacy technicians, pharmacists, doctors and nurses need to take into account when delivering the medicine.

Matthews said Health Canada, the Ontario College of Pharmacists, hospital leaders and Cancer Care Ontario are all looking into how the problem happened.

"Health Canada, in conjunction with the Ontario College of Pharmacists, visited [Hamilton, Ont-based supplier] Marchese Healthcare Solutions to look at their operations," a department spokesperson said in an email.

Patients were given doses of cyclophosphamide and gemcitabine that were lower than prescribed. The chemotherapy is part of a regime for breast and lung cancer as well as lymphoma and leukemia.

The commercially available premixed IV bags contained too much saline solution, which diluted the chemotherapy agent. One way the overdilution problem could occur is if excess or overfill volume is added to the premixed bags supplied to hospitals without clearly indicating how much overfill is present.

Doctors have been reassuring patients that any health consequences are unlikely.

Cancer recurrence worries

Tina Wells of Kingsville, Ont., is meeting with her oncologist today after learning she has been receiving diluted chemotherapy since February. Following a double mastectomy, Wells said cancer was found in her lymph nodes and she's continuing treatment as a precaution.

"I think that when something like this happens, it is unacceptable," Wells said in an interview. "Like I said, there should have been many checks so that this would not happen. Number 1 is, take responsibility for it."

Wells said she has joined a class-action lawsuit announced on Wednesday by the law firms Sutts, Strosberg LLP and Siskinds LLP to promote patient safety and monitoring of chemotherapy delivery.

Wells is worried that her chance of a recurrence of cancer has increased because of the error and if so, she wants to be compensated by the supplier.

"This issue involves only the volume and concentration of a high quality preparation, and those exist within very narrow boundaries of variation. Those variations were the result of the use of our preparation, which according to our current understanding was not consistent with the contract, the preparation or its labeling," Marita Zaffiro, the president of Marchese Hospital Solutions, said in a statement.

Lawyer Sabrina Lombardi of Siskinds in London, Ont. called the company's response all the more reason for a lawsuit.

"They're not stepping forward and acknowledging the error and the impact that it's having," Lombardi said. "We need to find out exactly what happened and that's what we hope to do through our investigations and as this litigation progresses."

Marchese was awarded a contract to supply sterile compounding services to hospitals.

Medbuy is a London, Ont.-based company that works with hospitals to reduce the cost of health-care supplies, such as the chemotherapy mixtures from Marchese.

"At this time, our concern is, first and foremost, patient welfare. Our member hospitals are concentrating their resources on assessing the impact of the situation — and providing the necessary care and support to their patients. We will provide such assistance as we can to our member hospitals," Medbuy said in a statement.

"Medbuy is currently investigating the situation, in collaboration with our member hospitals and the contracted supplier."

With files from CBC's Melanie Glanz and Amina Zafar