Invasive breast carcinoma - IARC

Fig. 1.02 Incidence of female breast cancer by age
in selected populations 1988-1993. From M. Parkin
et al. {2189}.
data it has clearly emerged that breast
cancer is a disease of affluent societies
which have acquired the We s t e rn
lifestyle, characterized by a high-caloric
diet rich in animal fat and proteins, combined
with a lack of physical exercise.
Regions which have featured this
lifestyle for a long period of time (Nort h
America, Nort h e rn Europe, Australia)
have reached a plateau of an incidence
rate of 70 to 90 new cases per 100,000
population/year while countries that
have more recently become industrialized
and affluent show a marked
i n c rease in incidence and mort a l i t y. In
addition to breast cancer, the We s t e rn
lifestyle carries a high risk of cancer
of the prostate, colon/rectum, and
endometrium. Specific enviro n m e n t a l
e x p o s u res operative in the development
of breast cancer (e.g. radiation, alcohol,
exogenous hormones) have been identified
but carry a lower risk.
More than most other human neoplasms,
breast cancer often shows familial clustering.
Two high penetrance genes have
been identified (BRCA1/2) which greatly
i n c rease the breast cancer risk (see
Chapter 8). However, it is anticipated that
multigenic traits also play a significant
role in the inherited susceptibility to
breast cancer.
Reproductive lifestyle
For almost half a century, the events of
re p roductive life have been considere d
to be risk factors for breast cancer in
women. Breast cancer occurs more frequently
among women who have an
early menarche, remain nulliparous or, if
p a rous, have few children with a late age
at first delivery. Infertility per se appears
to be a risk factor as may be lack of
b reast-feeding. Finally, late age at
menopause also increases the risk
{ 1 4 3 0 } .
Most of these factors have also been
found relevant in populations at low risk
of breast cancer such as the Japanese
and Chinese. Although the data is limited
in Africa, at least one study confirmed
the negative impact of late age at first
delivery, reduced number of pregnancies
and shorter breast feeding time
{2770}. Recent data indicates that the
age at any delivery, not just the first is
associated with breast cancer risk, with
deliveries occurring before the age of 30
having a protective effect {3137}.
Controversies still surround the issue of
abortion, some studies, but not others,
Fig. 1.04 Female breast cancer mortality trends.
Source: WHO/NCHS.
finding an increased risk for induced
abortion. Similarly, the protective effect of
lactation, once considered quite a strong
factor, was later given less importance;
its impact appears limited to long-term
cumulative breast feeding, pre f e r a b l y
exceeding two years {435}.
Exogenous hormones
Two major types of hormonal compounds
have been evaluated in re l a t i o n
to breast cancer: oral contraceptives
and menopausal replacement therapy.
The evidence suggests a small increase
in the relative risk associated with the use
of combined oral contraceptives, especially
among current and recent users,
which is not related to duration of use
and type or dose of preparation, and
may be partly linked to detection bias
{1296}. Data on injectable pure progestogen
contraceptives shows relative risks
from 1.0 to 1.3, which are not statistically
significant {1294}.
Epidemiological studies on postmenop
a u s a l e s t rogen therapy show a small
i n c rease in risk with longer duration of use
in current and recent users {1298}.
I n f o rmation on the effect of postmenopausal
estro g e n - p rogestogen therapy
was provided in only a minority of studies,
but indicates that the increased re l a t i v e
risk in long-term users is not significantly
d i ff e rent from that for long-term use of
e s t rogens alone {1297}. Yet it should be
noted that, among hormone re p l a c e m e n t
therapy users, there is an over re p re s e n t a-
tion of tumours that, with re g a rd to tumour
stage, type and grade are associated with
a more favourable prognosis {1760}.
Fig. 1.03 Aetiological factors involved in the development of breast cancer.
Nutrition
High intakes of fruit and vegetables are
p robably associated with a slightly
reduced risk of breast cancer {3153}.
14 Tumours of the breast