TAKING tamoxifen for 10 rather than five years halves the risk of
women dying from the most common kind of breast cancer. This is
according to new research being presented at this year’s ASCO
conference.
The Cancer Research UK study shows oestrogen receptor positive breast
cancer patients taking tamoxifen for longer than the recommended five
years are better protected against recurrence and are less likely to
die from the disease.
The ‘aTTom’ study looked at some 7,000 women with breast cancer
who, after five years of taking tamoxifen, either continued taking
the drug for another five years or stopped treatment.
Among women who took tamoxifen for 10 years, 25 per cent fewer had
recurrences of breast cancer and 23 per cent fewer died, compared to
women who took the drug for only five years.
Dr Daniel Rea, who is the clinical lead researcher based at the
University of Birmingham, said: “These results are important as
they establish that giving tamoxifen for longer than the current
standard of five years significantly cuts the risk of breast cancer
returning.
“Doctors are now likely to recommend continuing tamoxifen for an
extra five years and this will result in many fewer breast cancer
recurrences and breast cancer deaths worldwide. Tamoxifen is cheap
and widely available so this could have an immediate impact.”
75% of breast cancers are oestrogen
receptor positive and could benefit from hormone therapy. The female
sex hormone oestrogen encourages breast cancers to grow by activating
oestrogen receptors. Tamoxifen blocks these receptors, thus reducing
the chance of breast cancer returning after surgery or developing in
the other breast.
Despite the benefits of tamoxifen in preventing breast cancers from
returning, it does have side effects. Women taking tamoxifen
can experience side effects similar to menopausal symptoms, such as
night sweats and hot flushes. Rare but serious side effects of
tamoxifen include increased risk of endometrial cancer (cancer of the
lining of the uterus), blood clots, and stroke.
In this study no increase in the incidence of stroke was observed
with 10 years of tamoxifen therapy, though endometrial cancer risk
was higher in this arm. Endometrial cancer is often detected early,
when it can often be treated successfully. The researchers estimate
that for every endometrial cancer death that occurs as a side effect
of long-term tamoxifen, there would be 30 deaths from breast cancer
prevented.
Professor Richard Gray, based at the University of Oxford and
presenting the aTTom results at ASCO, said: “Five years of
tamoxifen is already an excellent treatment but there have been
concerns that giving it for longer might not produce extra benefits
and could even be harmful. The aTTom study establishes that the
benefits of taking tamoxifen for longer greatly outweigh the risks.”
Kate Law, director of clinical research at Cancer Research UK, said:
“Large clinical trials like aTTom are vitally important to
understand how drugs such as tamoxifen work and how best to use them.
We need these sorts of studies so we can be sure the benefits from
cancer drugs outweigh the side-effects that they may have.”
And commenting on the findings Dr Julia Wilson, Director of Research
at Breakthrough Breast Cancer, said: “These findings are extremely
exciting for women who are diagnosed with the most common type of
breast cancer.
“The study proved 10 years of taking tamoxifen has a much higher
survival rate than the current five years, which is vital in helping
us to stop breast cancer coming back and more importantly to help us
stop women dying of breast cancer.
“Tamoxifen is a well-established and cheap treatment, which means
the guidelines for usage should be easy to amend. We do however
encourage all women taking this treatment to speak to their doctor
about their individual circumstances as there can be side effects
involved.”
