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Safety aspects
On balance, this study is very reassuring. The finding that use
of the Pill does not increase the overall lifetime risk of breast
cancer is very positive, as is the fact that breast cancer in
users or former users of OCs is less likely to have metastasized
at the time of diagnosis. The risk of having breast cancer
diagnosed is slightly increased in current users of the Pill, but
not in those who used an OC 10 years ago. This suggests that
the Pill does not initiate cancer of the breast because the risk
of cancer following exposure to known carcinogens depends
upon the amount and overall duration of exposure and not
upon the length of time elapsed since exposure. It has been
hypothesized that the increased risk of breast cancer in
current users could reflect a higher likelihood of diagnosis as a
result of more frequent professional surveillance and selfexamination
in Pill users. Alternatively, the Pill may be acting
as a promoter of pre-existing breast cancer, thereby advancing
the time at which it becomes clinically detectable (but
conversely reducing its tendency to metastasize). It is not
possible to infer from these epidemiological data whether the
observed relation between breast-cancer risk and OCs is due
to an earlier diagnosis of breast cancer in ever-users, the
biological effects of OCs or a combination of reasons.
Confirmation from experimental studies is necessary.
OC use and
cervical cancer
OC use and
ovarian cancer
Cervical, ovarian and endometrial cancer
The relationship between cervical cancer and OC use is still
inconclusive. Although a slightly elevated risk of cervical
cancer has been reported with OC use (Brinton 1991;
Zondervan et al 1996), it is difficult to adjust for the
confounder of sexual activity, as having multiple partners is a
known risk factor for cervical cancer.
A study by Stanford (1991), investigating the risk of epithelial
ovarian cancer with OC use, showed that in women who have
ever used an oral contraceptive, the risk of ovarian cancer was
reduced by 30%. In addition, five or more years of use was
associated with a 50% reduction in risk. This protective effect
persisted for ten years or more after beginning use of OCs.
A second investigation confirmed this finding (Vessey and
Painter 1995). In comparison with never-users, the relative
risk of ovarian and endometrial cancer in users of OCs was
0.4 (95% CI 0.2–0.8) and 0.1 (95% CI 0.0–0.7), respectively.
There was also a strong negative relationship between the
duration of oral contraceptive use and ovarian-cancer risk, i.e.
in comparison with never-users, the relative risk in users of
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