Kate Warner, a 74-year-old breast cancer patient whose five rounds of chemotherapy ended last June, fears she will have to go back for more treatment after learning she received an underdose of her cancer drug.

"I am just getting ready to get my first haircut after growing for five months," the Windsor resident told CBC News. "I just don't want to lose it again."

But Warner, who doctors said responded well to the treatment, recently received the disturbing news that is arriving at hundreds of other homes — that some patients received watered down chemotherapy.

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Kate Warner hopes she doesn't have to go back for more chemotherapy. (CBC)

"I was surprised by a knock at the door with a hand-delivered letter from the cancer clinic, which threw me for a loop because when it is hand delivered I know it's important and scary," Warner said.

"It is unsettling. Then when I found out there were 1,000 people in Ontario alone that got the same letter, it's very depressing.

Patients in the Ontario communities of Oshawa, Peterborough, London and Windsor, as well as Saint John, N.B., were given lower than intended doses of cyclophosphamide and gemcitabine. The chemotherapy is part of a regime for breast and lung cancer as well as lymphoma and leukemia.

Doctors have been reassuring patients that any health consequences are unlikely. But Warner said she has many questions for her oncologist tomorrow, chiefly whether she'll need more chemotherapy.

The premixed bags contained too much saline solution, which diluted the chemotherapy agent.

"Our understanding is from the hospitals this drug may have been up to 20 per cent under the dose expected and hypothetically, one would imagine if only one dose was delivered at three per cent less than intended of a 12-dose regimen it would be very unlikely to have any impact, but it is difficult to speculate beyond that because of the unique circumstances of each patient," Dr. Carol Sawka, vice-president of clinical operations at Cancer Care Ontario, said in an interview today.

A pharmacy technician in Peterborough identified the error when an IV bag seemed too full.

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Dr. Carol Sawka of Cancer Care Ontario said all four Ontario hospitals immediately removed the medications received from the drug manufacturer when the problem was discovered late last month. (CBC)

"[In] the bag that they were using, the solution that had been provided by the supplier seemed to be a little bit larger than the other ones and so through some inquiry and due diligence on their part they felt that there was an issue and then they notified us because they knew that we were also using it and from there we all commenced to try and investigate what was actually happening," said Neil Johnson, vice-president of cancer care at London Health Sciences Centre.

The Institute for Safe Medication Practices Canada, an independent not-for-profit agency, said the source of the overdilution problem is the common manufacturing practice of including excess or overfill volume in commercially available IV bags.

"An opportunity exists to create and implement a national standard for labelling overfill," the institute said in a release Wednesday.

The labelling standard would make it clear to pharmacists, pharmacy technicians and nurses using the bags when there is overfill and by how much.

Politicians in Ontario are also discussing the situation for cancer patients.

"It's a very worrisome situation, obviously most worrisome for the patients and their families involved, and we will work to find out how this happened," said Ontario Premier Kathleen Wynne.

Questions have been raised about the impact the lower than intended doses of the chemotherapy drugs might have had on cancer patients.

Seeking answers

Cancer Care Ontario said the drugs, cyclophosphamide and gemcitabine, were watered down an estimated three to 20 per cent. The diluted chemotherapy was given to patients for at least a year in some of the hospitals.

Marchese Hospital Solutions, of Hamilton, Ont., said in a statement on its website Wednesday that it deeply regrets the uncertainty regarding chemotherapy solutions it supplied to hospitals in Ontario and New Brunswick.

"We must emphasize, despite some media characterizations to the contrary, there was never any question of a 'defective' medication. 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 labelling," the company said.

"We need to understand how assumptions about product use, which were not consistent with the contractually supplied preparation and labelling led to this issue."

Dr. John Dornan, chief of staff at Horizon Health Network's Saint John zone in New Brunswick, said the 186 patients who received the product in that province are being contacted.

"We have not seen any problems that we believe at this point in time are related to a dilution of the drug," Dornan said. He speculated an error in communication between the hospital and Marchese could have occurred and is under investigation.

Meanwhile on Wednesday, the law firm Sutts, Strosberg LLP and Siskinds LLP announced a class-action lawsuit to promote patient safety and monitoring of chemotherapy delivery.

The Canadian Breast Cancer Network also said it is vital for patients to be informed of the impact of diluted medications on their treatment outcomes and that adequate measures are taken to ensure the errors don't occur again.

With files from CBC's Kelly Crowe and Amina Zafar