world cancer report - iarc

SCREENING FOR BREAST CANCER
SUMMARY
> The epidemic increase in breast cancer
incidence has led to the introduction of
population-based mammography screening.
> The analysis of large randomized trials
has shown that in women aged 50 to 69
years, mammography screening can
reduce mortality from breast cancer by
25-30%. For women in the age group 40-
49 years the screening efficacy is significantly
less.
> The benefits of mammography in regional
or national screening programmes is
lower. Under optimal conditions with a
high compliance rate, a mortality reduction
of 20% appears achievable.
> There is only indirect evidence that
screening by clinical breast examination
will reduce the number of breast cancer
deaths.
Cancer of the breast is the most common
cancer in women worldwide and in many
regions, including Europe and Australia, it
is still the most common cause of death
from cancer in women. Until recently,
there has been little change in mortality
rates in spite of the steady improvement
in prognosis observed in recent years.
Breast cancer is characterized by early
systemic dissemination. As a result,
awareness of symptoms, and subsequent
diagnosis, often occur when disease is
advanced and metastatic. Mammography
(an X-ray examination of the breasts) can
detect preclinical cancer, that is, detect
the tumour before it is palpable, or before
it causes symptoms. Tumours detected
and treated at an early stage, can be
expected to be associated with a better
survival rate than those detected symptomatically.
Early diagnosis may permit
breast-conserving surgery (stage I disease),
reduce the need for adjuvant thera-
156 Prevention and screening
py or decrease complications related to
intensive treatment and recurrence [1].
Population-based mammographic screening
programmes were introduced in this
context.
The impact of screening
Since the 1970s, the incidence of breast
cancer has continued to increase. Only in
4 out of 70 populations assessed worldwide
was there an average change
between 1975 and 1990 of less than 0.5%
per year [2,3]. Steep increases of the
order of 3-5% per year have occurred in
some Asian countries (e.g. Japan,
Singapore), in Asian migrants to the USA
(Japanese, Chinese and Filipino) and
Southern Europe (Spain) (Fig. 4.31). In
some developed countries (e.g. England
and Wales, Finland, Denmark, The
Netherlands, USA), a clear change in the
speed of increase can be linked to the
introduction of mass screening that
occurred at different times in different
countries, e.g. in the early 1980s in the
USA, 1987-88 in England and Wales, early
1990s in The Netherlands. Some increase
is attributable to reduced fertility and
changing dietary habits. However, mam-
Fig. 4.31 Populations exhibiting the largest
increases in the incidence of breast cancer
between 1975 and 1990.
Fig. 4.30 Mammography, an X-ray examination of
the breasts, is used to screen for breast cancer.
©GE Medical Systems
mography is the main determinant of
these relatively recent increases as indicated
by trends in the incidence of in situ
cancers [4,5].
Mortality has not consistently paralleled
incidence trends everywhere. In fact, in
some developed countries rates have
been rather stable, even with incidence on
the increase. No clear overall decline in
mortality had been observed in any place
before the late 1980s, when a smooth
downturn occurred in Europe, North
America and Australia. Such changes
before the era of mammography can be
attributed to a progression towards early
diagnosis that took place in the 1970s,
particularly in young generations. More
recently, in the early 1990s, a drastic fall
in mortality was seen in the UK and North
America [6,7]. However, the fall occurred
too soon after the widespread availability
of mammography to be a consequence of
it; rather, the success of adjuvant therapy
based on chemotherapy and tamoxifen is
the likely major cause of this trend.
Protocols for screening
As currently practised, population-based
screening for breast cancer is based on
mammographic examination, at prescribed
intervals, of all women within a