Induced abortion and breast cancer

Sir The study by Bra€ uner et al. in the June 2013 issue (1) is to be welcomed as throwing some light on breast cancer incidence among women who have had induced abortions, when linking of such records tends to be difficult. In Denmark there are national registry data available. This was accessed to retrieve records of breast cancer and immigration, but not for abortion. Linking to national records for abortion would also remove much of potential underreporting of abortions among the women in the study who did not report induced abortions. Bra€ uner et al. conclude (in their Abstract) that “Our study did not show evidence of an association between induced abortion and breast cancer risk.” But the findings are not very conclusive: the 95% confidence intervals for all the hazard ratios for all the subgroups and the whole study group straddle 1.0. Underreporting of abortions in the study could further widen the confidence intervals. With regard to parity, the authors “excluded women who did not have children in order to make the frame of reference uniform.” It seems women who have had nulliparous abortions, which increase their breast cancer risks, can then reduce these risks by having children later. It would also have been interesting to investigate the breast cancer incidence of women who remain nulliparous and childless. The authors report that the incidence of breast cancer was “higher in the study population” but do not say how much higher. Genes influence breast cancer. Perhaps in the Copenhagen area there is a concentration of families and kinship groups with a high disposition to breast cancer. The exact comparison between the study group and the national population as to breast cancer incidence would be interesting. The comparison with national data for the subgroups who have had abortions would also be valuable. Additionally, in situ carcinomas of breast ducts are now more frequently seen with the advent of digital scanning machines, and merit attention. With a larger cancer group that includes the in situ carcinomas, more precise comparisons with the non-cancer group can be made. Whereas this study was limited to the cohort with 25 576 final participants from the 79 729 invited initially, the whole Danish population is covered by the national registers. By investigating and controlling for the various factors in a national context, a more conclusive analysis with narrower confidence intervals for the hazard ratios could be achieved. Such a study could be powerful enough to resolve the issue of breast cancer after abortion, as the authors would have liked: “Ideally we could have linked the self-reported data with the register on Legally Induced Abortions.” It seems they were denied the necessary official approval to retrieve the abortion records of the women in their study. This suggests a lack of political will to access national registers for a national study which could effectively resolve the issue.