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A new US study suggests that breast cancer risk is not increased by induced abortion or miscarriage, contrary towards the findings of some other studies and also the claims made by some groups.
The study is published inside the Archives of Internal Medicine.
Researchers from Brigham and Women’s Hospital, Harvard Medical School along with the Harvard School of Public Wellness, Boston in Massachusetts, utilized data from the Nurses’ Health Study II (NHS II) on 105,716 women who were aged between 29 and 46 years and cancer-free in the start with the ten-year follow-up which started in 1993.
The cohort is described by the researchers as “predominantly premenopausal”, since most with the females had not started the menopause throughout the follow-up.
Records for the large scale prospective study were updated by questionnaire response every two years, and contained information on spontaneous abortions (miscarriages) and induced abortions, such as any that had occurred before the period of study.
A large scale prospective study is considered high standard for this kind of research due to the fact you start having a large group of healthy participants and you monitor them for a great part of their lives to see who develops the symptoms below investigation.
This study covered 973,437 person-years of follow-up between 1993 and 2003.
(The number of person years of a study is an indication of its size and it is not unusual for researchers to talk about events per person year, that is the total number of events being counted divided by the total number of years of data from each and every participant.)
The results showed that:
– 1,458 new circumstances of invasive breast cancer occurred for the duration of the follow-up.
– 16,118 participants (15 per cent) reported a history of induced abortion.
– 21,753 (21 per cent) reported a history of spontaneous abortion (miscarriage).
– Neither abortion nor miscarriage was linked significantly with breast cancer.
– The results were unaffected by number of abortions or miscarriages, age of woman when the events occurred, along with other factors.
In summary, the researchers found no significant link between abortion, miscarriage and breast cancer across the group. However, they did report two subgroup effects.
One subgroup showed a link between induced abortion and progesterone receptor-negative breast cancer, the kind of cancer that doesn’t respond to the hormone progesterone.
The other subgroup showed a link between miscarriage before the age of 20 and lower breast cancer risk.
But in each instances the researchers suspect the results are spurious, due to chance, due to the fact the numbers inside the two groups are too low to give a confident statistical finding.
Their overall conclusion therefore was that:
“Among this predominantly premenopausal population, neither induced nor spontaneous abortion was associated using the incidence of breast cancer.”
About the Nurses’ Well being Study II (NHS II)
The NHS II is really a prospective study cohort of more than 116,000 females enrolled in 1989.
The purpose with the NHS II study is to look in the link between potentially modifiable risk factors and any major well being problems that arise amongst females in early adult life. Breast cancer and melanoma are two particular areas of interest towards the researchers.
The participants fill in questionnaires about their way of life, dietary habits, life events, exercise, use of contraceptives, and wellness issues every two years.
Adverse health events such as cancer diagnosis are followed up with a lot more detailed investigation of medical records, and blood samples are analysed from about 30,000 of the cohort.
90 per cent response rate has been maintained for the questionnaire follow-ups.
“Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Females: A Prospective Cohort Study.”
Karin B. Michels, Fei Xue, Graham A. Colditz, and Walter C. Willett.
Arch Intern Med. 2007;167:814-820.
Vol. 167 No. 8, April 23, 2007
click here for Abstract.
Click here for far more info on Nurses’ Health Study II: Risk Factors for Breast Cancer Amongst Younger Nurses (National Cancer Institute, US).
Written by: Catharine Paddock
Writer: Medical News Today
Copyright: Medical News Today
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