Purpose: The risk of 12 types of cancer in relation to use of monthly injectable contraceptives was assessed in a prospective study in Shanghai, China.
Methods: From 1989 to 1991, an in-person interview was administered to 267,400 female textile workers to ascertain information on risk factors for breast cancer, contraceptive use and induced abortions. The cohort was followed until July 2000 for incident cancer cases. Cox proportional hazards analysis was used to calculate incidence rate ratios for specific types of cancer in women who ever had used monthly injectable contraceptives and by length of use.
Results: There was a reduced risk of uterine corpus cancer for women who had ever used monthly injectable contraceptives. No association was observed between the use of monthly injectable contraceptives and the risk of all cancers combined and for any of the 11 other cancers considered.
Conclusion: There appears to be no evidence of an increased risk of cancer after exposure to monthly injectable contraceptives in our study.