BALTIMORE--Breast cancer is preventable, says Johns Hopkins epidemiologist
Jonathan Samet, MD. "But we don't yet know how to do it."
This paradox arises, in part, from the rapid changes seen in breast
cancer patterns worldwide that may point to an important role
for environmental risk factors and suggest the potential for primary
disease prevention, Dr. Samet said at a conference on neoplastic
disorders sponsored by Johns Hopkins Medical Institutions.
Studies offer clues as to the predictors of breast cancer risk,
Dr. Samet said, but even when risk factors are identified, we
as a society and women as individuals may not be ready to take
the necessary steps to modify them significantly. And some important
risk factors such as family history are not subject to alteration.
A woman's reproductive history can be used to help predict her
risk of breast cancer, he said. Early menarche is associated with
increased risk, and the age of menarche has been falling over
the last century.
Other factors include later menopause, later age at first pregnancy,
nulliparity (especially for women over 40), high parity for women
before menopause, and low parity for women after menopause. (Lactation
may confer some protection.)
These reproductive risk factors suggest that exposure to estrogen
(and possibly progesterone) plays some role in the onset of breast
cancer. Thus, factors that reduce the lifetime exposure to estrogen
may be helpful. Exercise during adolescence, for example, may
delay menarche and result in fewer overall menstrual cycles.
"However, these factors are not easily modified," Dr.
Samet said. "It just isn't socially acceptable to propose
early childbearing, for example, as a form of breast cancer protection."