Many Canadian women with breast cancer are already getting the best chemotherapy treatment available, according to an international study that compared three different drug combinations.

AC/T, a chemotherapy regimen commonly used in breast cancer patients, is significantly less successful at preventing cancer from recurring than another Canadian-developed combination, the study suggests.

While the findings will serve to fine-tune treatment rather than stake out new ground, they should help lead to more women being offered the more effective combination of chemo drugs, oncologists said.

The researchers, from Canada and the United States, reported their findings Sunday at a major breast cancer conference in San Antonio, Texas.

The women being studied — 2,104 in Canada and the United States — had undergone surgery to remove a breast cancer tumour and were getting chemotherapy to lower the risk their cancer would come back. The women, aged 60 and younger, all had cancer that had spread into their lymph nodes or tumours that had characteristics suggesting the cancer would likely spread.

Women received one of three treatments

The study set out to test an experimental chemo regimen against two established chemo combinations, as well as assessing the two commonly used treatments against each other.

The women received one of the three treatments:

• One, called AC/T, consists of treatment by the drugs doxorubicin and cyclophosphamide followed by paclitaxel. This combination is commonly used in the United States but is less frequently used in Canada. 
• The Canadian-developed regiment is called CEF, short for cyclophosphamide, epirubicin and fluorouracil. It is commonly used in this country.
• The experimental combination, called EC/T, involved a shorter, concentrated course of epirubicin and cyclophosphamide followed by paclitaxel.

The study suggests that for every 100 women who received the experimental combination or the Canadian-developed regimen, 10 would have had a recurrence.

But the chance of the disease recurring jumps for women on the AC/T regimen. The study suggests 15 of every 100 women treated would have seen their cancer come back.

On Monday, Canadian oncologists discussed the AC/T findings.

"Clearly we won't be using that in the future unless there's other reasons that might make it appropriate for an individual," Dr. Sandy Paterson of the Alberta Cancer Board told CBC News.

Major differences at 30 months, researchers say

After an average of only 30 months followup, a difference was already clear, the researchers said.

At that point, 70 women on EC/T and 79 on CEF had had a recurrence and 112 on AC/T saw their cancer return.

It will be important to follow the women to see whether there is a difference in death rates due to breast cancer among the three groups, oncologists said.

About 22 per cent of invasive breast cancer cases in Canada are similar to those in the study, according to the Canadian Cancer Society.

N.B. woman 'didn't even hesitate' to join study

Kristina Cusack of Summerville, N.B., was one of them.

Cusack, 34, was diagnosed with breast cancer two years ago. Her oncologist, Dr. Margot Burnell of Saint John Regional Hospital, asked whether Cusack would be willing to take part in a study.

"I had a daughter at home and I'm just thinking if I can change it so that 20 years down the road she doesn't even have to think about this or any of her friends have to think about this, then that's a good thing," Cusask said. 

Cusack was given the Canadian-developed regimen. Two years out, she has not had a recurrence.

AC/T still good regimen: lead researcher

It is too soon to say whether EC/T or CEF is more effective, said Burnell, the lead researcher.

Unlike the study's other lead investigator, Dr. Mark Levine, an oncologist at McMaster University in Hamilton, Burnell said she thought AC/T would continue to be widely used because of its lesser side-effects.

The researchers will continue to follow the study participants to try to tease out an answer to that question as well as to see if there was a survival advantage to either combination.

The study was funded by the Canadian Cancer Society, the Canadian and American National Cancer Institutes and drug makers Pfizer, Bristol-Myers Squibb, Amgen, Janssen Ortho and Ortho Biotech.

With files from the Canadian Press