Study raises concerns about alternative therapies for breast cancer
Women with breast cancer who take mega-doses of vitamins and minerals
to help battle their disease may be doing more harm than good, suggests
a study led by a UVic researcher.
The study, recently published in the international journal, Breast Cancer
Research and Treatment, was led by Dr. Mary Lesperance, a statistician
in UVic’s department of mathematics and statistics. “Alternative
therapies are commonly used by women with breast cancer, but their effect
on survival and recurrence have rarely been carefully evaluated,”
says Lesperance. “Our study is the first to look at it in such a
controlled way.”
The study’s premise was simple: if mega-doses are beneficial, then
patients taking them in combination with conventional cancer treatment
should live longer and have lower recurrence rates than patients receiving
conventional therapy alone.
The study measured survival and relapse times for two groups of Vancouver
Island women diagnosed with unilateral (one breast only), non-metastatic
cancer between 1989 and 1998. All women in both groups were receiving
conventional breast cancer therapies through the Vancouver Island Centre
of the BC Cancer Agency, but the test group—90 women in total—also
sought and received mega-vitamin prescriptions within 180 days of diagnosis
from an orthomolecular physician. Orthomolecular medicine is the prevention
and treatment of disease by administering nutritional supplements.
The 90 women were prescribed varying amounts of beta-carotene, niacin
B3, vitamin C, selenium, coenzyme Q10 and zinc. For some women, the prescribed
vitamin C dose was as high as 24 grams a day—320 times the recommended
daily dose for a healthy adult woman.
Each of these 90 women was matched by age at diagnosis, stage of disease
and type of treatment to two women in the control group that was receiving
conventional treatment only.
The results surprised everyone. The overall survival at five years was
81 per cent for the control group, but only 72 per cent for the mega-vitamin
group. When the margin of error is factored in, the gap narrows, but still
shows a slight advantage for the control group. A similar pattern is evident
in the 10-year survival rates.
The study also calculated the “hazard ratios,” or relative risk
of dying, faced by each group. “If the hazard ratios were 1.0, then
the two groups would be at similar risk of dying,” says Lesperance.
“But the hazard ratios for the mega-vitamin group were estimated
at 1.75, which means they face a slightly higher risk than the controls.”
Lesperance cautions that there were some unmeasured variables in the study—for
example, there was no guarantee that prescribed vitamin doses were followed,
or that women in the control group didn’t take vitamins on their
own.
More definitive answers about the role of vitamins and minerals would
come from a clinical trial. “That’s the kind of effort needed
to really sort out whether these alternative therapies are beneficial
or harmful, or have no effect at all,” says Dr. Ivo Olivotto, one
of two oncologists from the BC Cancer Agency who helped design the study.
“This study at least begins to address the question in a methodical
way.”
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