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Million Women Study Collaborators
Correspondence to: Prof Valerie Beral, Cancer
Research UK Epidemiology Unit, Gibson Building, Radcliffe
Infirmary, Woodstock Road, Oxford OX2 6HE, UK
Summary
Background Current use of
hormone-replacement
therapy (HRT) increases the incidence of
breast cancer.
The Million Women Study was set up to investigate
the effects of specific types of
HRT on incident
and fatal breast cancer.
Methods 1 084 110 UK women aged 50-64 years were recruited
into the Million Women Study between 1996 and 2001,
provided information about their use of
HRT and other
personal details, and were followed up for
cancer incidence
and death.
Findings Half the women
had used Hormone Replacement Therapy; 9364 incident invasive
breast cancers
and
637 breast cancer deaths were registered after an average
of 2•6
and 4•1
years of follow-up, respectively. Current
users of HRT at recruitment were more likely than never
users
to develop
breast cancer (adjusted relative
risk 1•66
[95% CI 1•58-1•75], p<0•0001)
and die from it (1•22 [1•00-1•48],
p=0•05). Past users of HRT were, however, not
at an increased risk of incident or fatal
disease (1•01
[0•94-1•09] and 1•05 [0•82-1•34],
respectively). Incidence was significantly
increased for current users of preparations containing
oestrogen
only (1•30 [1•21-1•40], p<0•0001),
oestrogen-progestagen (2•00 [1•88-2•12],
p<0•0001), and tibolone (1•45 [1•25-1•68],
p<0•0001), but the magnitude of the associated
risk was substantially greater for oestrogen-progestagen
than for other types of Hormone Replacement Therapy (p<0•0001). Results
varied little between specific oestrogens
and progestagens or their doses; or between
continuous and sequential
regimens.
The relative risks
were significantly increased separately for oral,
transdermal,
and implanted oestrogen-only
formulations (1•32 [1•21-1•45]; 1•24
[1•11-1•39]; and 1•65 [1•26-2•16],
respectively; all p<0•0001).
In current users
of each type of HRT the risk of
breast cancer
increased with increasing total duration
of use.
10 years' use
of
Hormone Replacement
Therapy is estimated to result in
five (95% CI 3-7) additional
breast cancers per 1000
users of oestrogen-only
preparations and 19 (15-23) additional
cancers
per 1000 users of oestrogen-progestagen
combinations. Use
of HRT by women aged 50-64 years
in the UK over the past decade has resulted in an estimated
20 000 extra
breast cancers, 15,000 associated
with oestrogen-progestagen;
the extra deaths cannot yet be reliably
estimated.
Interpretation: Current
use of
HRT is associated with
an increased risk of incident and fatal
breast cancer;
the effect is
substantially greater for oestrogen-progestagen
combinations than for other types of
HRT.
HRT Doubles Danger of Breast Cancer:
Study
(Excerpt from
Herald 12 August 2003)
Women taking the
most common form of
hormone replacement therapy
in Britain are twice as likely to develop
breast
cancer, the world's largest study on the
treatment's risks has concluded. An extra 2000
British women a year are developing the disease
because of
HRT, researchers have warned.
The results have
prompted New Zealand authorities to consider
whether medical advice for women taking Hormone Replacement Therapy
drugs should be reviewed. The risks associated
with the combined oestrogen-progestogen Hormone Replacement Therapy are
far higher than previously thought and begin
much earlier than doctors had assumed.
Tens of thousands of
New Zealand women take some form of combined
HRT
therapy. Breast cancer is the biggest killer of
women in Britain, with 1000 deaths a month from
the disease. In New Zealand, about 2000 women
are diagnosed with breast cancer each year and
about 600 die from it.
This week, the
British Government's Committee on Safety of
Medicines sent emails and faxes telling all
National Health Service doctors and other health
professionals of the new findings, published in
the Lancet. (See above)
The advice stops
short of telling doctors to take women off
combined HRT. Dr. Mary Armitage, chairwoman of
the committee's steering group on HRT,
said for most women the benefits outweighed the
risks for short-term use. Long-term, however,
women needed to discuss other options with their
doctors, she said. NZ Health Ministry spokesman
Dr. Stewart Jessamine said the British study
would be considered at the meeting of the
Medicines Adverse Reactions Committee next month
to see if advice needed to be changed.
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