How oral contraceptives can influence cancer risk?
Oral contraceptives are used to prevent birth control. It
also sometimes used to treat heavy or irregular menstruation or endometriosis.
However, there are some studies found that oral contraceptives could slightly
increase the risk of breast cancer among young women. The development and
growth of cancer cells are can be influenced naturally by estrogen and progesterone.
Oral contraceptives don’t always cause cancer. It also
depends on how the individual control their lifestyles.
The use of oral contraceptives can reduced the risk of
endometrial and ovarian cancer whereas it can increase the risk of breast,
cervical and liver cancer.
Breast cancer risk
The development of breast cancer among women can depend on
several factors and some of them are related to the natural hormones. Hormonal
and reproductive history factors that increase risk of breast cancer include
factors that may allow breast tissue to be exposed to high levels of hormones
for longer periods of time, such as:
- Beginning menstruation at early age
- Experiencing menopause at late age
- Later age at first pregnancy
-
Not having children at all
In an epidemiologic data in 1996 analysis from more than 50
studies worldwide by the Collaborative Group on Hormonal Factors in Breast
Cancer discovered that women who were current or recent users of oral
contraceptives had a slightly higher risk of developing breast cancer than
women who had never take the medication[1]. The risk was highest for
women who started to take this medication since teenagers.
However, 10 or more
years after women stopped taking oral contraceptives, their risk to breast
cancer had returned to the same level as if they never used the birth control
pills, regardless of family history of breast cancer, reproductive history,
geographic area of residence, ethnics, differences in study design, dose and
type of hormones used or duration of use. In addition, breast cancer diagnosed
in women who had stopped using oral contraceptives for 10 or more years were
less advanced than women who had never used oral contraceptives.
Ovarian cancer risk
Oral contraceptives use has consistently been found to be
associated with a reduced risk of ovarian cancer. From 20 studies in an 1992
analysis, the researchers found that the longer a woman uses oral
contraceptives, the risk of ovarian cancer is decreased. The risk is decreased
by 10-12% after a year of use and by approximately 50% after 5 years of use.
Researchers
have studied how the amount or type of hormones in oral contraceptives affects ovarian
cancer risk. One study in the Cancer and Steroid Hormone (CASH) found that the
reduction in ovarian cancer risk was the same regardless of the type or amount
of estrogen or progestin in the pill[2].
A more recent analysis of data
from the CASH study, however, indicated that oral contraceptive formulations
with high levels of progestin were associated with a lower risk of ovarian
cancer than formulations with low progestin levels[3].
In another
study, the Steroid Hormones and Reproductions (SHARE) Study, researchers
investigated new, lower-dose progestins that have varying androgenic (testosterone-like)
effects. They found no difference in ovarian cancer risk between androgenic and
non-androgenic pills[4].
Endometrial cancer risk
Women who use
oral contraceptives have been shown to have a reduced risk of endometrial
cancer. This protective effect increases with the length of time oral
contraceptives are used and continues for many years after a woman stops using
oral contraceptives
Cervical cancer risk
An
increased risk of cervical cancer is associated with long-term use of oral
contraceptives of about 5 years. An analysis of 24 epidemiologic studies found
that the longer a woman uses oral contraceptives, the higher her risk of
cervical cancer. However, among women who stopped taking oral contraceptives,
the risk tend to decline over time, regardless of how long they had used oral contraceptives
before stopping.
In
a 2002 report by the International Agency for Research on Cancer, which is part
of the World Health Organization (WHO), data from 8 studies were combined to
assess the association between oral contraceptive uses and cervical cancer risk
among women infected with the human papillomavirus (HPV). Researchers found a
nearly threefold increase in risk among women who had used oral contraceptives
for 5-9 years compared with women who had never used oral contraceptives. Among
women who had used oral contraceptives for 10 years or longer, the risk of
cervical cancer was four times higher.
Almost all
cervical cancers are caused by persistent infection with high-risk, or
oncogenic, types of HPV, and the association of cervical cancer with oral
contraceptive use is likely to be indirect. The hormones in oral contraceptives
may change the susceptibility of cervical cells to HPV infection, affect their
ability to clear the infection, or make it easier for HPV infection to cause
changes that progress to cervical cancer.
Liver cancer risk
Oral
contraceptive use is associated with an increase in the risk of benign liver tumors, such as hepatocellular adenomas.
Benign tumors can form as lumps in different areas of the liver, and they have
a high risk of bleeding or rupturing. However, these tumors rarely become
malignant.
Whether
oral contraceptive use increases the risk of malignant liver tumors, also known
as hepatocellular carcinomas, is less clear. Some studies have found that women
who take oral contraceptives for more than 5 years have an increased risk of
hepatocellular carcinoma, but others have not.
