New research from a large scale study in the US found no evidence of a link between incomplete pregnancy, such as that from induced abortion, and risk of breast cancer, which the researchers said should put an end to the much debated issue.
The study was conducted by researchers from the new department of cancer etiology at the City of Hope Comprehensive Cancer Center, Duarte, California, and colleagues, and is published in the June issue of the journal Contraception.
Despite mounting evidence from large prospective studies of no link between induced abortion and breast cancer risk, public concern continues, said lead investigator Katherine DeLellis Henderson and colleagues, explaining the reason for the study.
They wrote that, “much of the data prompting this concern came from case-control studies, many of which may have been affected by bias or design flaws,” reported Medwire News.
These have given rise to two beliefs about women who have incomplete pregnancies. First, that they don’t have as much long-term protection against breast cancer as they would from full term pregnancies; and second, that their breasts are exposed to high hormone levels of early pregnancy and then don’t benefit from the terminal cell differentiation of late pregnancy, possibly making them more vulnerable to cancer causing chemicals.
For this study, the researchers examined breast cancer as it relates to incomplete pregnancy, including the total number of induced abortions, age at first induced abortion and total number of miscarriages among participants of the ongoing California Teachers Study (CTS), a prospective study of current and former public school teachers or administrators who are with the California State Teachers Retirement System.
DeLellis Henderson and colleagues looked at data taken from the CTS baseline questionnaires in 1995-96 where the women had responded to detailed questions about pregnancy history, including incomplete pregnancy. By linking the CTS records with the California Cancer Registry, the researchers found 3,324 women from the CTS study diagnosed with incident breast cancer up to 2004.
Using a statistical tool known as Cox multivariable regression, they found no statistically significant link between any measure of incomplete pregnancy and breast cancer risk.
The researchers adjusted for established risk factors including ethnicity, first degree family history of breast cancer, and age at onset of menstrual periods (menarche).
They found that having an induced abortion at first pregnancy did not increase risk of breast cancer neither among those women who went on to have full term pregnancies, nor those who never went on to give birth.
Also, miscarriage in a first pregnancy did not increase risk for breast cancer in either of these groups.
The researchers said their findings supported those from a recent large scale study of nurses, the Nurses Health Study II.
They concluded that:
“Our results provide further, strong evidence that neither induced abortion nor miscarriage is associated with breast cancer risk and may help to resolve any remaining uncertainty as to whether such a relationship exists.”
“Incomplete pregnancy is not associated with breast cancer risk: the California Teachers Study.”
DeLellis Henderson K, Sullivan-Halley J, Reynolds P, Horn-Ross PL, Clarke CA, Chang ET, Neuhausen S, Ursin G, Bernstein L.
Contraception, Volume 77, Issue 6, Pages 391-396 (June 2008).
Source: journal abstract, Medwire News.
Response by The Coalition on Abortion/Breast Cancer
Written by: Catharine Paddock, PhD