Long-Term Injectable Use Does Not Increase Risk Of Breast Cancer, But It May Lower Bone Density

Abstract

1 hospital in Nairobi Kenya; Mexico City Mexico and Chiang Mai Thailand and 2 hospitals in Bangkok Thailand took part in a WHO sponsored collaborative study to examine the association between depomedroxyprogesterone acetate (DMPA) and breast cancer. The researchers compared 1979-1988 data on 869 hospitalized women with breast cancer with 11890 hospitalized women with unrelated conditions. 12.5% of cases and 12.2% of controls had ever had an injection of DMPA. Overall ever users had no significant increased risk of breast cancer (relative risk [RR] 1.2) In addition risk did not rise with duration. Nevertheless current users who began receiving DMPA within the past 4 years did have a significantly higher risk (RR 2.6). On the other hand current users who began receiving DMPA >5 years earlier were not at increased risk at all. For example the RR for those who began 8-12 years earlier was 0.8 and for those who began >12 years earlier was 0.5. Further even though the current users 2 times as likely to have breast cancer than their corresponding counterparts who did not use DMPA (RR 2.2) the risk according to duration was not significant. The researchers listed some possible reasons for the discrepancies. They concluded that there is only a weak association between DMPA and breast cancer--comparable to that between oral contraceptives and breast cancer. In New Zealand a case control study of 30 25-51 year old women who used DMPA for at least 5 years showed that long term use of DMPA significantly reduced bone density. For example for DMPA users the spine and femoral neck bone densities were 8% and 7% respectively lower than the premenopausal controls. The researchers found the same effect even when they restricted the analysis to nonsmokers.