Levonorgestrel, Pharmacokinetics, Efficacy and Safety 59than for other types of hormone therapy. For each type of hormone treatment,
the risk of breast cancer increased with increasing total duration of use [153].
The risk of breast cancer with hormone therapy varies with the type of
progesterone. Fournier et al. reported that the risk of breast cancer was
significantly greater with hormone replacement therapy containing synthetic
progestins than with hormone replacement therapy containing micronized
progesterone, the RRs being 1.4 [1.2–1.7] and 0.9 [0.7–1.2] respectively [154].
Whether the use of hormonal contraceptives increases the risk of breast
cancer later in life, when the incidence of breast cancer is increased has been
principally studied. Previous epidemiological studies suggested that women
who currently use OCP or who have used them in the previous 10 years have a
slightly increased risk of breast cancer, whereas women who have used OCP
less recently do not have an increased risk [155, 156]. Later a widely
conducted population-based, case–control study reported that current or
former oral contraceptive use was not associated with a significantly increased
risk of breast cancer. Their data showed strong evidence that former oral-
contraceptive use does not increase this risk later in life, when the incidence of
breast cancer is higher [157].
In a systematic review which included 6 studies on the use of progestin
and breast cancer risk. Five of the six studies reported no association between
progestin-only formulations (including norethindrone oral contraceptives,
depot medroxyprogesterone acetate, injectable, LNG system users,
implantable and IUDs) and breast cancer risk [158]. While Soini et al. reported
that LNG-IUD use was associated with a higher than expected incidence of
breast cancer. They examined the association between premenopausal use of
the LNG-IUD and cancer incidence in Finland. The standardized incidence
ratio for breast cancer among all LNG-IUD users was 1.19 (95% CI 1.13-1.25;
1,542 observed compared with 1,292 expected cases) [159]. In a later study,
the same group reported that the levonorgestrel IUD users had an increased
risk for both ductal breast cancer and for lobular breast cancer as compared
with the general female population [160].
Safety of LNG Emergency Contraception
LNG has a significantly lower incidence of side effects compared to
combination-method ECs [161]. In a randomized, double-blind clinical trial
with full results for 1956 women at 21 sites worldwide, LNG (specifically
Plan B) demonstrated a superior safety profile relative to the Yuzpe regimen