BOSTONWomen who receive postlumpectomy radiotherapy to their
left breast are not at greater risk of heart attacks, according to a study
presented by Katherine Vallis, MD, at the annual meeting of the American
Society for Therapeutic Radiology and Oncology (ASTRO).
Dr. Vallis, a radiation oncologist at Princess Margaret
Hospital, Toronto, Ontario, and her colleagues found nearly identical rates of
myocardial infarction (MI) in 1,074 women treated for left-sided breast cancer
and 1,054 for right-sided breast cancer between 1982 and 1988 at Princess
Margaret Hospital. The rates were also similar to those found in the general
"Whenever the left breast is treated, a small part of the
heart receives some radiation," Dr. Vallis noted. "There was concern
that the radiation might cause subtle damage to the heart, therefore increasing
the risk of heart attack in these women."
The Princess Margaret results contradict previous studies that
found women were at greater risk after radiotherapy for cancer of the left
breast. Also from Ontario, a population-based study published in 1999 found
that these patients had twice the risk of their counterparts treated for cancer
of the right breast.
"Some of the earlier studies included mainly
postmastectomy radiotherapy patients," Dr. Vallis said, "and some of
them have included patients treated with radiation therapy techniques that
would now be considered obsolete." She also speculated that one reason her
results differ from the province-wide study might be that the groups used
different databases and methods.
The Princess Margaret study linked to the Canadian Institute
for Health Information Hospitalization File and the Ontario Mortality Database.
It validated the cardiac events with the original hospital
records, using diagnostic criteria from the Multinational Monitoring of Trends
and Determinants in Cardiovascular Disease (MONICA) Project.
Dr. Vallis said that an Ontario-wide study using methods
similar to the Princess Margaret Hospital study is now underway.
The median follow-up in the Princess Margaret study was 10.7
years, and the median age of the 2,128 women in the cohort was 54. All had
lumpectomies for early-stage breast cancer; 63% were node negative. Most
patients (92%) received a radiotherapy dose of 40 Gy in 16 fractions delivered
using a pair of coplanar tangential opposed fields. The other 8% received 50 Gy
in 25 fractions.
A five-fraction 12.5 Gy boost to the tumor bed followed the
shorter protocol in 84% of cases. In 6%, treatment was also delivered to the
supraclavicular fossa, the axilla, or both; the internal mammary nodes received
therapy in 2.5% of cases. The overall survival rates were 81% at 5 years and
67% at 10 years.
The researchers identified 70 MIs in 56 patients following
radiation therapy. Of these, 53 met MONICA criteria for definite MIs, 6 were
possible MIs, and 11 definitely were not MIs.
Definite or possible MIs were recorded for 26 patients treated
to the left breast. These included 8 fatal MIs. In the right-breast group, 23
patients had definite or possible MIs, of which 6 were fatal. There were more
MIs in women over 60, which, Dr. Vallis noted, was to be expected.
"We can say conclusively from this study of a large group
of patients that, using these modern techniques, we haven’t found any
increased risk for heart attack even many years later," Dr. Vallis
concluded. "And if there is an effect, it must be a small one because we
haven’t been able to detect it."