Nearly 1,000 patients in Ontario undergoing chemotherapy within the last year for diseases that included cancers of the breast, lung and bladder received watered-down treatment containing a lower dose of medication than was prescribed, Ontario's cancer care agency revealed Tuesday.

Seventeen patients at Windsor Regional Hospital alone have died since starting their therapy.

The defective intravenous treatment was discovered by a pharmacy technician at a Peterborough hospital late last month. The premixed cocktail of medication, shipped out to at least four hospitals in Ontario and one in New Brunswick by a Mississauga supplier, contained too high a percentage of saline solution, diluting the chemotherapy agent.

If you or one of your family members has received watered-down chemotherapy, we want to hear from you. Please email reporters Diana Zlomislic at dzlomislic@thestar.ca .

The majority of the chemo patients, 665, were being treated at London Health Sciences Centre , where the incorrect dosage had been administered since March 1, 2012.

Nearly 300 more were given the diluted medication at Windsor Regional Hospital beginning on Feb. 24, 2012. Thirty-four patients at Oshawa’s Lakeridge Health hospital, one patient at Peterborough Regional Health Centre , and 186 patients at a New Brunswick hospital were also given the watered-down chemotherapy.

All of the hospitals are in the process of contacting the affected patients or their families.

David Musyj, president and CEO of Windsor Regional Hospital, said 17 patients from his hospital have died since starting their treatment.

“I can’t imagine what (those families) will have to go through when they’re just dealing with the loss of their loved one, to be told the chemotherapy treatment was watered down,” he said. “Even though probably we’ll never know if it contributed to their deaths or not, that still will not make it less painful.”

He said some patients had more than 20 rounds of the defective chemo. Collectively, the hospital estimates the 290 patients combined received more than 1,000 treatments. The majority of the 290 patients were being treated for breast cancer.

Neil Johnson, vice-president of cancer services at London Health Sciences Centre, does not know how many patients have died over the course of the treatment.

As a pharmacist, he said the error is concerning.

“I’ve been licensed since 1998 and never seen anything like this. As a health leader, a health administer, I’ve never seen anything like this,” he said.

The liquid drug was prepared by Marchese Hospital Solutions. In a statement, spokesperson Greg Wilkinson said the company is “deeply concerned whenever any question is raised about the quality of our work.”

“We are collaborating closely with our partners to address the issues which have been raised. Our preliminary investigation of this issue leads us to be confident that we have met the quality specifications of the contract we are honoured to have been awarded.

“Following further inquiries, by our partners and Marchese, we will have more to report in a few days’ time,” he said.

The two drugs that were diluted as much as 20 per cent are cyclophosphamide, commonly used to treat breast cancer, as well as types of leukemia and lymphoma, and gemcitabine, used to treat lung and bladder cancers. Treatments typically include combining these drugs with up to three others.

Among Windsor Regional Hospital cancer patients taking both of those drugs was 27-year-old Crystal Giegerich, who died in February.

She was six months pregnant in the fall of 2011 when she was diagnosed with stage four breast cancer. Doctors waited about a month, then delivered her baby prematurely so she could begin chemotherapy.

Her husband, Rob Giegerich, a pharmacist for the past 23 years, said he has not yet heard from the hospital but is eager to find out if his wife received the defective product.

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“I’d like to have some answers as to what the effect could have been if she had received the appropriate dose,” he said. “Could it have made a difference of weeks or months?”

Giegerich said they had been hoping to get Crystal into a clinical trial run out of a medical centre in Detroit.

Dr. Carol Sawka, vice-president of clinical operations at Cancer Care Ontario , said the agency is investigating if other hospitals are affected, but is confident no others are impacted.

All Ontario hospitals involved immediately stopped using the defective treatment and have found the necessary medication to continue therapy, meaning there will be no disruptions. Windsor has found a new supplier and London is mixing the compound at its in-house pharmacy.

The hospitals are attempting to contact all past and current patients affected this week. Patient phone lines and after-hours clinics have also been set up. Windsor Regional says its oncologists will be working extra hours, seven days a week.

Dr. Leta Forbes, medical director of oncology at Lakeridge Health, said the lower doses likely had no significant impact on the effectiveness of the treatment of the 34 patients affected. None of the patients had more than two doses of the weaker treatment, and some had only one.

“It was a very minimal underdosing. The patients would not have noticed any change in side effects of the treatment, and we don’t expect there would be any change in effectiveness.”

Doctors sometimes prescribe underdosing of up to 25 per cent of a medication if the patient experiences significant side effects, Forbes added.