Breastfeeding – Another Reason for BRCA1 Carriers to Strongly Consider It
The FORCE Facebook page posted a link to a new study led by Dr. Steven Narod and colleagues that examines the impact of breastfeeding on breast cancer risk in BRCA1 and BRCA2 carriers. The new study is an important contribution to the research literature in this area, so we thought it would be worth discussing in some detail.
First, let’s go over some of the known benefits of breastfeeding – for both the infant and mom – in the general population.
Known Benefits of Breastfeeding in the General Population
Studies in the general population have revealed a number of benefits of breastfeeding to both mother and infant. A few of them are:
Breastfeeding Benefits to Infant
- Transfers proteins and antibodies to infant that help protect against microorganisms
- Decreases risk for a number of acute illnesses – including ear infections, gastroenteritis, and respiratory illnesses
- Improves gastrointestinal function by increasing the rate of stomach emptying, increasing the activity of the enzyme that breaks down milk in the baby’s GI tract, and decreasing the permeability of the infants intestine if premature
- For premature infants, decreases the risk of necrotizing enterocolitis
Breastfeeding Benefits to Mother
- Accelerates recovery of uterus from childbirth (via breastfeeding stimulation of oxytocin hormone release)
- May enhance post-pregnancy weight loss and tends to prolong lack of ovulation after pregnancy (note that this is not a completely reliable form of birth control though)
- Thought to reduce maternal hormonal stress response
- Reduction of breast cancer risk
- Possibly reduction of ovarian cancer risk
- May be a protective factor against osteoporosis
Breastfeeding is also associated with an economic benefit to the family (via not needing to buy formula and also via fewer illnesses in the infant).
Previous Studies Have Been Mixed on Whether Breastfeeding May Have a Protective Effect On Breast Cancer Risk in BRCA1 Carriers
Several previous studies have looked at the relationship between breastfeeding and breast cancer risk in BRCA1 and carriers.
Two studies – one of which was particularly limited by small size – found no association between breastfeeding and breast cancer risk in BRCA1 carriers:
- Drs. Nadine Andrieu and Jenny Chang-Claude and their colleagues found no association between breastfeeding and breast cancer risk in a retrospective cohort study of 1601 women (1187 with BRCA1 mutations and 414 with BRCA2 mutations)
- Dr. Giske Ursin (then at the University of Southern California) and colleagues reported the results of a study that found no association between breastfeeding and breast cancer in BRCA1/BRCA2 carriers, but which seems remarkably underpowered to do so (only 94 women with identified BRCA1 or BRCA2 mutations in the study and they were grouped together)
A 2004 study by Dr. Steven Narod and colleagues did find a significant association between breastfeeding and breast cancer risk for BRCA1 carriers, but not for BRCA2 carriers. In this study, the researchers studied a total of 965 matched pairs of women. The matching was done on the following features: mutated gene (685 pairs had BRCA1 mutations and 280 pairs had BRCA2 mutations), country of residence, and year of birth (plus or minus 2 years). The researchers also performed an additional analysis of a subset of the pairs that could be matched on number of births (since this is itself related to breast cancer risk.
In this study, there was evidence that length of breastfeeding was associated with a lower breast cancer risk in BRCA1 carriers (but not in BRCA2 carriers).
Given the different results from the Andrieu et al. study mentioned above and because matching on number of births (which is a cleaner analysis given the association of this variable with breast cancer risk) significantly decreased the number of pairs that were available for analysis, they sought to increase the size of the study much further and have now presented the results of that analysis.
A New International Study Provides Further Evidence Suggesting Breastfeeding May Help Prevent Breast Cancer in BRCA1 Carriers Who Have Not Undergone Risk-Reducing Bilateral Mastectomy
The new study expands upon the previous study by Dr. Narod and colleagues and is a case-control study of a total of 1,665 pairs of women (1,243 pairs with a BRCA1 mutation and 422 pairs with a BRCA2 mutation). The studied women were from 7 different countries and had been interested in BRCA1/BRCA2 testing due to their personal and/or family history of breast or ovarian cancer. For each pair, one member of the pair is a BRCA1 or BRCA2 carrier with an invasive breast cancer diagnosis. The other member of each pair had no history of breast cancer and was also a carrier of a mutation in the same gene. Women who had not had children were not eligible. The pairs were matched up on the basis of the following: (1) mutation in the same Hereditary Breast and Ovarian Cancer gene; (2) birth year (within 1 year maximum); (3) number of births; and (4) country of residence.
Here are a few key results:
- In the BRCA1 pairs, the average breastfeeding duration was significantly shorter amongst the women with breast cancer (8.8 months compared to 10.4 months). Thus, on average the BRCA1 carriers with breast cancer spent 1.6 months fewer breastfeeding than the BRCA1 carriers without breast cancer. This was a statistically significant difference.
- For BRCA1 carriers, breastfeeding for 1 year or more cut breast cancer risk by about one-third.
- For BRCA2 carriers, there was not a significant association between breastfeeding and breast cancer risk.
Bottom Line Implications for BRCA1 and BRCA2 Carriers
1. There are a number of reasons related to maternal, infant, and economic benefits that suggest that breastfeeding is very important.
2. The new study described above is the largest study to date focusing on the impact of breastfeeding on breast cancer risk in BRCA1 and BRCA2 carriers considered seperately and should provide the best information that we have at this time relevant to breastfeeding and breast cancer risk for women with Hereditary Breast and Ovarian Cancer.
3. This study suggests that BRCA1 carriers may derive very important breast cancer risk reduction benefits from breastfeeding – particularly for at least one year.
4. Breastfeeding does not seem to affect breast cancer risk in BRCA2 carriers. However, there are numerous other maternal and infant benefits of breastfeeding that still make it a great thing to do.
5. The decrease in risk cited for breastfeeding BRCA1 carriers is relevant to BRCA1 carriers who have chosen not to have a bilateral risk-reducing mastectomy.
As with all things at BRCAscoop, it’s very important to discuss the specifics of this information with your doctor. Only you and your doctor, in the context of your personal medical history can determine whether breastfeeding is right for you.
How We Know This:
Kotsopoulos J, Lubinski J, Salmena L, et al. Breastfeeding and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers. Breast Cancer Research 2012; 14:R42.
Andrieu N, Goldgar DE, Easton DF, et al. Pregnancies, breast-feeding, and breast cancer risk in the International BRCA1/2 Carrier Cohort Study (IBCCS). Journal of the National Cancer Institute 2006; 98:535-44.
Jernström H, Lubinski J, Lynch HT, et al. Breast-feeding and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers. Journal of the National Cancer Institute 2004; 96:1094-8.
Lee E, Ma H, McKean-Cowdin R, et al. Effect of reproductive factors and oral contraceptives on breast cancer risk in BRCA1/2 mutation carriers and noncarriers: results from a population-based study. Cancer Epidemiology Biomarkers & Prevention 2008; 17:3170-8.
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