The glandular components of the adult female
breast are the lactiferous glands, which can pro-
duce and secrete milk, and the lactiferous ducts,
which store milk. Fatty tissue accumulates around
these structures, called lobules. Supportive con-
nective fibers called Cooper ligaments group the
lobules into lobes. Each breast contains between
15 and 20 lobes. Milk production, called lactation,
occurs under the stimulation of PROLACTIN, a HOR-
MONEthe PITUITARY GLANDbegins to secrete after
CHILDBIRTH. Lactation may continue for as long as
the woman continues BREASTFEEDING. Another hor-
mone, OXYTOCIN, stimulates the release of milk
from the breast. The breasts may become signifi-
cantly larger (up to three times their prepregnancy
size) while the woman is breastfeeding. When
breastfeeding stops the lactiferous structures
(glands and ducts) shrink and the breasts return to
their normal size.
The breasts are also sources of sexual stimula-
tion and arousal for women and for men, both by
touch and visually. During sexual arousal and at
ORGASM the nipples become firm and erect. A
woman’s breasts may become uncomfortably ten-
der and sometimes swollen during the luteal
phase of the MENSTRUAL CYCLE, in response to the
elevation of estrogens in the BLOODcirculation.
At MENOPAUSEthe glandular tissue in the breast
shrinks and the breast structure becomes much less
dense. At this time a woman’s risk for BREAST CAN-
CER increases significantly. Current preventive
health guidelines recommend routine MAMMOGRAM
(X-RAYof the breast) beginning at age 40 for most
women, and beginning earlier and occurring more
frequently in women who have high risk for devel-
oping breast cancer. Health experts recommend
that all women, beginning at the conclusion of
puberty, perform monthly BREAST SELF-EXAMINATION
as a method of early detection for BREAST HEALTH
concerns, including lumps that may be cancerous.
HEALTH CONDITIONS THAT CAN AFFECT THE BREASTSBREAST CANCER fibroadenoma
FIBROCYSTIC BREAST DISEASE GYNECOMASTIA
INTRADUCTAL PAPILLOMA MASTALGIA
MASTITIS PAGET’S DISEASE OF THE BREAST
For further discussion of the breast within the
context of the structures and functions of repro-
duction and sexuality, please see the overview sec-
tion “The Reproductive System.”
See also LIGAMENT; PREMENSTRUAL SYNDROME
(PMS); TURNER’S SYNDROME.breast cancer A malignant (cancerous) tumor
that arises in the BREAST. There are many types of
breast cancers, some of which are HORMONEdriven
(draw sustenance from ESTROGENSor PROGESTERONE)
and others that are not. Primary breast cancer
originates in the breast; secondary breast cancer
metastasizes (spreads) to the breast from an origin
elsewhere in the body. Breast cancer may also
metastasize to other sites in the body such as the
LUNGSor bones.
Breast cancer is the most common cancer
among American women; doctors in the United
States diagnose breast cancer in about 200,000
women each year. Breast cancer is currently sec-
ond to LUNG CANCERas the leading cause of deaths
due to cancer among women. However, signifi-
cant advances in the early 2000s in understand-
ing the mechanisms of breast cancer cells and the
resulting development of new treatments are
changing the landscape of breast cancer.
Genetic factors The genes BRCA- 1 /BRCA- 2 were
the first genes conclusively linked to cancer.
Inherited mutations in these genes significantly
increase a woman’s risk for breast cancer and
OVARIAN CANCER. Researchers continue to study
these mutations for ways to take advantage of
them for preventing or treating cancers in women
who have either or both mutations.
Other mutations are not hereditary but instead
occur over time, the consequence of molecular
damage that becomes cumulative over time.
Researchers have identified nearly two dozen
genes that influence cell proliferation (cell growth
and division) in some way. One of the most signif-
icant is the her-2GENE(human epidermal growth
factor receptor 2, also called HER-2/neu) gene,
located on CHROMOSOME 17. The her-2 gene
expresses (directs the production of) certain pro-
tein receptors on the surfaces of cell membranes.
The receptors allow binding with the HER-2/neu
protein, a protein that instructs the cell to grow
and divide. Mutations in the her-2 gene cause
increased numbers of HER-2/neu receptors on
cells, allowing greater HER-2/neu binding. This250 The Reproductive System