The comprehensive study bears out previous suspicions of a link between
combination (progestagen-oestrogen) hormone replacement therapies (HRTs) and the
development of breast cancer.
The use of HRT by British women aged between 50 and 64 has caused an
estimated 20,000 extra breast cancers over the past decade, 15,000 of which are
likely to be associated with combination HRT therapies, the study found.
The study is also the first to report that HRT increases the risk of dying
from breast cancer.
The 'Million Women Study' led by Valerie Beral from Cancer Research UK's
Epidemiology Unit in Oxford, southern England, focused on the effects of
specific types of HRT on breast cancer.
Beral monitored 1,084,110 British women aged between 50 to 64, from 1996 to
2001, half of whom had followed HRT at some point in their lives.
Of the women surveyed, 9,364 developed breast cancer after an average 2.6
years, with 637 women dying of the disease after an average of 4.1 years.
Current users of all types of HRT were at an increased risk of developing
breast cancer, and faced a 22 percent increased risk of dying from the disease.
Use of combination HRT caused a four-fold increase in the risk of developing
the disease compared to oestrogen-only HRT, the study shows.
The study found that the risk of breast cancer rose in proportion to the
length of the HRT use, but that the increased risk appeared to wear off a few
years after discontinuing the therapy.
Commenting in The Lancet, Beral said: "Combined HRT is usually prescribed for
women who still have a uterus, to avoid the increased risk of cancer of the
uterus caused by oestrogen-only therapy".
"Since our results show a substantially greater increase in breast cancer
with combined HRT, women need to weigh the increased risk of breast cancer
caused by progestogen against the lower risk of uterine cancer."
"Comparing the risks is by no means simple," Beral added, "and women may well
want to discuss their options with their doctor."
The implications for medical practitioners are discussed in a commentary by a
Dutch scientist published alongside Beral's article.
To Chris van Wheel from the University of Nijmegen, the Netherlands, the
problem lies with women who are already taking HRT -- an estimated 20 to 50
percent of all Western women aged between 45 and 70.
Van Wheel recommended that this group discontinue HRT use as soon as
possible, although practitioners should introduce the issue in a positive,
supportive way in order to avoid panic reactions.
The Dutch scientist also sees "a great need for a public information
campaign", with the medical profession in the lead, with current evidence of
increased risks stated "in clear but unsensational wording".
