On 2014 Mar 08, David Reardon commented:

Findings in Doubt Due to Failure to Account for Interrelationships Between Breast Cancer, Smoking & Abortion

Like similar studies exploring the association between smoking and breast cancer, this study by Kawai et al¹ unfortunately fails to explore a very important and intertwined risk factor: abortion history.

Numerous studies have shown that young women report starting or smoking more in order to cope with feelings associated with past abortions.

For example, a very recent longitudinal study published in the Journal of Adolescent Health revealed young women with a history of abortion had adjusted higher 4.1 times higher risk of smoking (CI, 1.9-8.8) and 4.5 times higher risk of nicotine dependence (OR 4.5; CI, 2.1-9.6).² Similar results are reported by others.³(4) In one post-abortion follow-up study, nearly one fourth of the women specifically described that they used smoking to "deal with" feelings related to their abortions.⁵

The importance of examining the three-way associations between smoking, abortion history and breast cancer is underscored by the controversy regarding statistical associations between abortion history and breast cancer. That controversy was recently reignited by meta-analysis of 36 studies conducted in China which found a significant association between abortion and breast cancer, including a dose effect. ⁶

To my knowledge, while plenty of researchers have explored the associations between smoking and breast cancer and abortion and breast cancer, none have yet to look at both risk factors in the same study. This is a serious problem, especially if one of these factors is actually just a proxy for the other.

Clearly, whether smoking and abortion arise from common risk factors or from causal interactions, the fact that they are associated in any fashion raises important research questions:

• Is the elevated risk of breast cancer associated with abortion due to behavioral changes (such as increased smoking) with the biological mechanism behind the elevated breast cancer rate due to smoking? or

• Is the apparent elevated risk of breast cancer associated with smoking really due to increased exposure to abortion in the population of smoking women and it is abortion (perhaps due to disruption of early pregnancy hormone cycles) contributing a biological mechanism that accounts for all or part of the observed increased cancer risk associated with smoking?, or

• Is there a combination of incidental associations and/or overlapping biological risk factors?

In my view, it clear that new analyses must be done which, when looking at the abortion history variable, segregate smokers from non-smokers. This would show if abortion has an independent effect. Similarly, when looking at the smoking history, the analyses should include segregation of smokers and non-smokers relative to history of 0, 1, or 2+ abortions.

It is my hope that Dr. Kawai's team, and others with similar data sets, will begin to explore these interactions.

References

(1) Kawai M, Malone KE, Tang MT, Li CI. Active smoking and the risk of estrogen receptor-positive and triple-negative breast cancer among women ages 20 to 44 years. Cancer. 2014 Feb 10. doi: 10.1002/cncr.28402.

(2) Olsson CA, Horwill E, Moore E, Eisenberg ME, Venn A, O'Loughlin C, Patton GC. Social and Emotional Adjustment Following Early Pregnancy in Young Australian Women: A Comparison of Those Who Terminate, Miscarry, or Complete Pregnancy. J Adolesc Health. 2014 Jan 15. pii: S1054-139X(13)00738-6. doi: 10.1016/j.jadohealth.2013.10.203.

(3) Pedersen, W. Childbirth, abortion and subsequent substance use in young women: a population-based longitudinal study. Addiction. 2007 102: 1971–1978.

(4) L Henriet, M Kaminski. Impact of induced abortions on subsequent pregnancy outcome: the 1995 French national perinatal pregnancy survey, Br J Obstet Gynaecol 2001 108:1036-1042.

(5) Major B, Richards C, Cooper ML et al. Personal resilience, cognitive appraisals, and coping: An integrative model of adjustment to abortion. J Person Soc Psychol, 1998; 74: 735-752.

(6) Huang Y1, Zhang X, Li W, Song F, Dai H, Wang J, Gao Y, Liu X, Chen C, Yan Y, Wang Y, Chen K. A meta-analysis of the association between induced abortion and breast cancer risk among Chinese females. Cancer Causes Control. 2014 Feb;25(2):227-36. doi: 10.1007/s10552-013-0325-7. Epub 2013 Nov 24.

On 2014 Mar 08, David Reardon commented:

Findings in Doubt Due to Failure to Account for Interrelationships Between Breast Cancer, Smoking & Abortion

Like similar studies exploring the association between smoking and breast cancer, this study by Kawai et al¹ unfortunately fails to explore a very important and intertwined risk factor: abortion history.

Numerous studies have shown that young women report starting or smoking more in order to cope with feelings associated with past abortions.

For example, a very recent longitudinal study published in the Journal of Adolescent Health revealed young women with a history of abortion had adjusted higher 4.1 times higher risk of smoking (CI, 1.9-8.8) and 4.5 times higher risk of nicotine dependence (OR 4.5; CI, 2.1-9.6).² Similar results are reported by others.³(4) In one post-abortion follow-up study, nearly one fourth of the women specifically described that they used smoking to "deal with" feelings related to their abortions.⁵

The importance of examining the three-way associations between smoking, abortion history and breast cancer is underscored by the controversy regarding statistical associations between abortion history and breast cancer. That controversy was recently reignited by meta-analysis of 36 studies conducted in China which found a significant association between abortion and breast cancer, including a dose effect. ⁶

To my knowledge, while plenty of researchers have explored the associations between smoking and breast cancer and abortion and breast cancer, none have yet to look at both risk factors in the same study. This is a serious problem, especially if one of these factors is actually just a proxy for the other.

Clearly, whether smoking and abortion arise from common risk factors or from causal interactions, the fact that they are associated in any fashion raises important research questions:

• Is the elevated risk of breast cancer associated with abortion due to behavioral changes (such as increased smoking) with the biological mechanism behind the elevated breast cancer rate due to smoking? or

• Is the apparent elevated risk of breast cancer associated with smoking really due to increased exposure to abortion in the population of smoking women and it is abortion (perhaps due to disruption of early pregnancy hormone cycles) contributing a biological mechanism that accounts for all or part of the observed increased cancer risk associated with smoking?, or

• Is there a combination of incidental associations and/or overlapping biological risk factors?

In my view, it clear that new analyses must be done which, when looking at the abortion history variable, segregate smokers from non-smokers. This would show if abortion has an independent effect. Similarly, when looking at the smoking history, the analyses should include segregation of smokers and non-smokers relative to history of 0, 1, or 2+ abortions.

It is my hope that Dr. Kawai's team, and others with similar data sets, will begin to explore these interactions.

References

(1) Kawai M, Malone KE, Tang MT, Li CI. Active smoking and the risk of estrogen receptor-positive and triple-negative breast cancer among women ages 20 to 44 years. Cancer. 2014 Feb 10. doi: 10.1002/cncr.28402.

(2) Olsson CA, Horwill E, Moore E, Eisenberg ME, Venn A, O'Loughlin C, Patton GC. Social and Emotional Adjustment Following Early Pregnancy in Young Australian Women: A Comparison of Those Who Terminate, Miscarry, or Complete Pregnancy. J Adolesc Health. 2014 Jan 15. pii: S1054-139X(13)00738-6. doi: 10.1016/j.jadohealth.2013.10.203.

(3) Pedersen, W. Childbirth, abortion and subsequent substance use in young women: a population-based longitudinal study. Addiction. 2007 102: 1971–1978.

(4) L Henriet, M Kaminski. Impact of induced abortions on subsequent pregnancy outcome: the 1995 French national perinatal pregnancy survey, Br J Obstet Gynaecol 2001 108:1036-1042.

(5) Major B, Richards C, Cooper ML et al. Personal resilience, cognitive appraisals, and coping: An integrative model of adjustment to abortion. J Person Soc Psychol, 1998; 74: 735-752.

(6) Huang Y1, Zhang X, Li W, Song F, Dai H, Wang J, Gao Y, Liu X, Chen C, Yan Y, Wang Y, Chen K. A meta-analysis of the association between induced abortion and breast cancer risk among Chinese females. Cancer Causes Control. 2014 Feb;25(2):227-36. doi: 10.1007/s10552-013-0325-7. Epub 2013 Nov 24.