Long-term case-controlled surveillance of users of Medroxyprogesterone Acetate Injectable Suspension, USP found slight or no increased overall risk of breast cancer3 and no overall increased risk of ovarian,4 liver,5 or cervical6 cancer and a prolonged, protective effect of reducing the risk of endometrial7 cancer in the population of users.
A pooled analysis14 from two case-control studies, the World Health Organization Study3 and the New Zealand Study13, reported the relative risk (RR) of breast cancer for women who had ever used Medroxyprogesterone Acetate Injectable Suspension, USP as 1.1 (95% confidence interval (CI) 0.97 to 1.4). Overall, there was no increase in risk with increasing duration of use of Medroxyprogesterone Acetate Injectable Suspension, USP. The RR of breast cancer for women of all ages who had initiated use of Medroxyprogesterone Acetate Injectable Suspension, USP within the previous 5 years was estimated to be 2.0 (95% CI 1.5 to 2.8).
The World Health Organization Study3, a component of the pooled analysis14 described above, showed an increased RR of 2.19 (95% CI 1.23 to 3.89) of breast cancer associated with use of Medroxyprogesterone Acetate Injectable Suspension, USP in women whose first exposure to drug was within the previous 4 years and who were under 35 years of age. However, the overall RR for ever-users of Medroxyprogesterone Acetate Injectable Suspension, USP was only 1.2 (95% CI 0.96 to 1.52).
[NOTE: A RR of 1.0 indicates neither an increased nor a decreased risk of cancer associated with the use of the drug, relative to no use of the drug. In the case of the subpopulation with a RR of 2.19, the 95% CI is fairly wide and does not include the value of 1.0, thus inferring an increased risk of breast cancer in the defined subgroup relative to nonusers. The value of 2.19 means that women whose first exposure to drug was within the previous 4 years and who are under 35 years of age have a 2.19 fold (95% CI 1.23 to 3.89-fold) increased risk of breast cancer relative to nonusers. The National Cancer Institute8 reports an average annual incidence rate for breast cancer for US women, all races, age 30 to 34 years of 26.7 per 100,000. A RR of 2.19, thus, increases the possible risk from 26.7 to 58.5 cases per 100,000 women. The attributable risk, thus, is 31.8 per 100,000 women per year.]
A statistically insignificant increase in RR estimates of invasive squamous-cell cervical cancer has been associated with the use of Medroxyprogesterone Acetate Injectable Suspension, USP in women who were first exposed before the age of 35 years (RR 1.22 to 1.28 and 95% CI 0.93 to 1.70). The overall, nonsignificant relative rate of invasive squamous-cell cervical cancer in women who ever used Medroxyprogesterone Acetate Injectable Suspension, USP was estimated to be 1.11 (95% CI 0.96 to 1.29). No trends in risk with duration of use or times since initial or most recent exposure were observed.