The study reported a slightly increased risk of cervical cancer in situ (cancer confined to the epithelium, the surface layer of the cervix)—1.25 among women with symptoms (statistically significant). To avoid screening bias—more detection of cancer in situ without symptoms among DMPA users because they were seeing providers more regularly than nonusers—the researchers emphasize the findings for women who had symptoms at diagnosis. The researchers conclude from these findings—increased risk of in situ but not invasive cancer—that the in situ lesions induced by DMPA may be reversible or that they do not lead to invasive cancer (304). Other studies of cervical cancer among DMPA users have found no significant increased risk of cervical dysplasia (precancerous lesions) (221, 222), cancer in situ, or invasive cancer (227).

Monthly injectables. The only published study devoted exclusively to monthly injectables concluded that users may have a slightly increased risk of cervical cancer (relative risk of 1.3). The report, which analyzed data collected in the WHO study, involved women in Chile and Mexico who had used a monthly injectable containing dihydroxyprogesterone acetophenide and an estrogen, usually estradiol enanthate (300).

The protective effect of DMPA may be even stronger than the WHO study suggests. All three DMPA users who had endometrial cancer had also taken estrogen to regulate bleeding. Estrogen increases risk of endometrial cancer (317).