By Tracy G. Cassels
If someone told you certain things would increase the risk of developing breast cancer, would you avoid it? Some of you would say yes regardless of what it was, some would say it depends, and some wouldn’t care. As adults and humans, we’re bound to play the odds. Is the convenience worth the increase in risk? If it isn’t, we’ll avoid it, but sometimes we accept that is. Smokers know that they stand a higher chance of developing lung cancer if they smoke, but to some of them, the cost of quitting is greater than the reduction in risk they’ll have. Why? Because despite all the ads and public health warnings, cancer isn’t as deadly and pervasive as health officials make it out to be. Now, don’t get me wrong, the risk is real and it’s there, but many of us go our lives without thinking of it. And those we know who get it may not do so until later in life and many will get better. So we weigh the odds. This is part of the reason why, despite a plethora of studies outlining the fact that not breastfeeding serves to increase the risk of breast, cervical, uterine, and endometrial cancer, not all women choose to breastfeed. Now some don’t do so because they are unaware of the benefits those two boobs can provide for them, but some know of the risk and choose not to breastfeed anyway because in their view, the risk is so minimal that it’s not worth their perceived hassle of breastfeeding. After all, many of us have the belief that we are, at least to a certain degree, invincible.
But what if you were told certain choices would increase the risk of your child developing acute lymphoblastic leukemia (ALL) or acute meyloblastic leukemia (AML) or Hodgkin’s disease or other neuroblastomas? These are, after all, some of the most common forms of childhood cancer in Western societies. What would you do then? I imagine all but the most cold or completely logic-driven parents would respond that they would make the choices that didn’t increase the chance that their child would experience such a fate. After all, seeing your child sick with the cold can be heart-wrenching; imagining them suffering through a potentially life-threatening disease is beyond comprehension for most. Because of that, for many parents no cost is too great, regardless of the size of increase in risk. And yet, despite what they say, the average Western parent makes choices that increase this risk, because in our culture, most parents are not breastfeeding for an extended time. In hopes that the reason for this is sheer ignorance, I’d like to take the time to share the research on how two boobs can help reduce the risk of your child developing certain types of childhood cancer.
The Evidence (Notably here I will revert to using the language of the research which uses a “reduced risk” model for breastfeeding, despite it being the other way around as breastfeeding is the norm. Part of this is so people who read the original sources are not confused, but also because when I provide odds-ratios, I can just take them from the articles and not have to work out what the flip side would be.)
I do believe that one of the main reasons this knowledge is hard to come by is that the research may be seen as equivocal. Not all findings support the notion that breastfeeding reduces the risk of childhood cancer, but much of that is due to methodological limitations, not because the relationship doesn’t exist. For example, data from the Oxford Survey of Childhood Cancers (OSCC) in the UK looked at the data from thousands of children to try and establish a link between breastfeeding and cancer. Sadly, the authors found no relationship at all by any length of breastfeeding (examined at < 1 month, 1-6 months, and >= 7 months). [Though a couple things about this study are worth mentioning: a) they removed cases in which symptoms of cancer occurred in the first nine months or the child died in the first year, which may be where the effects of breastfeeding are strongest (though I certainly don’t know this for a fact, but it is reasonable), and b) they did not examine exclusive breastfeeding, but rather any breastfeeding. The latter is important as the effects of breastfeeding are known to be strongest when breastfeeding is exclusive. It is also difficult to ascertain how little or how much women were breastfeeding when any breastfeeding is the variable of interest.] However, researchers in China found a slight reduction in risk for lymphoma for those infants ever breastfed which was slightly greater for longer-term breastfeeding. Notably, the effects pertained primarily to Hodgkin’s disease and there was no relationship to acute leukemia. Interestingly, breastfeeding rates in China in the mid-1990s were relatively high compared to the US (though it did seem to vary by region) (any: 94%, 82%, and 72% at 1, 4, and 6 months) suggesting that the effects of breastfeeding would be harder to find because the incidence of breastfeeding was quite high. Returning to the UK, other researchers examined various factors predicting incidents of childhood cancer in a national cohort. They examined breastfeeding, but only breastfeeding in the first week of life. Despite the short time-frame, 46% of controls received breastmilk in the first week while only 28% of children who developed cancer received any breastmilk. This early influence of breastmilk highlights the potential flaw in the OSCC data which excluded children who were symptomatic in the first year of life; if exposure to breastmilk in the first week of life is related to a decreased risk of developing cancer later on, it may be particularly salient in the first year.
The research from China and the UK is enhanced by more conclusive evidence from the US and India. A case-controlled study in the US examined the role of breastfeeding by dividing groups into > 6 months breastfeeding, 6 months breastfeeding, and artificial feeding. Compared to the > 6 months group, there was an increased risk of all types of cancers for the 6 months breastfeeding and artificial feeding groups. Despite the results being significant across all types of cancer, the results seemed to be driven primarily by a large significant protection for lymphoma. An Indian case study examining childhood cancer rates and the effects of breastfeeding also found a significant effect of average duration of breastfeeding and an even larger effect for exclusive breastfeeding on distinguishing between the two groups. Again, while the results translated across the entire group, they were driven by the highly significant relationship between breastfeeding and lymphoma, as an examination of breastfeeding and all other types of cancer was non-significant.
While the evidence seems to be strong for lymphomas, the data for the most common type of childhood cancer – leukemia – is more controversial. While not looking at breastfeeding directly, one UK study examined how infections in the first year of life predicted later development of ALL. The authors found that children who later developed ALL had a significantly greater number of clinically-diagnosed infections in the first year of life (i.e., we’re not talking about the common cold). Given the relationship between breastfeeding and a reduction in infections, it seems plausible that breastfeeding may also reduce the incidence of ALL, despite previous non-significant results. While the previous studies failed to find evidence of protection for ALL and AML childhood cancers, Xiao Shu and colleagues examined data from the Children’s Cancer Group (which collects data from the United States, Canada, and Australia) for possible breastfeeding benefits. They found no significant association between ever breastfeeding and AML status and only a very slight protective benefit for ALL. However, when duration of breastfeeding was examined, children who had breastfed for longer than six months had a 43% reduction in risk for AML and a 28% reduction in risk for ALL.
Why would this study find a relationship that none of the aforementioned studies did? It seems that even within ALL and AML, there are subtypes that are differentially affected by exposure to breastmilk. Shu and colleagues also performed an analysis by subtype of ALL and AML, something previous research had failed to do. What they found was that the reduced risk in AML cases only existed for certain subtypes, namely myeloblastic with no maturation, myeloblastic with minimal maturation, and myeloblastic with maturation. Similarly, extended breastfeeding protected only against Early Pre-B-Cell ALL and having ever breastfed only provided protection against Pre-B-Cell ALL. This means that while breastfeeding may not provide protection for all types of leukemia, it does offer protection against many of the subtypes of acute leukemia, and thus some of the previous research may have been made up of children suffering from the other types of ALL and AML. In line with this research, and perhaps more conclusively, researchers at UC Berkeley performed a meta-analysis of 14 studies examining the relationship between breastfeeding and two types of childhood cancer: ALL and AML. [For those who are unaware, a meta-analysis is considered the gold standard of conclusiveness for research as it combines the data from many studies and analyzes them together. This means that any individual flaw or bias in any one article gets weighed out by the many other studies in the meta-analysis. Of course, a meta-analysis is only as good as the collective data included and so one must be sure that stringent criteria were met to decide what to include. The UC Berkeley meta-analysis can be said to have done just that.] They divided the data by short- (<= 6 months) and long-term (> 6 months) breastfeeding and found significant negative relationships between breastfeeding and both ALL and AML. While results were significant for both short- and long-term breastfeeding, the results were much stronger for long-term breastfeeding.
Given this data, we must ask ourselves why so few parents are made aware of this information. One of the problems may be that, for unknown reasons, researchers seem hesitant to believe or support their findings. In another meta-analysis the authors reported having found no effect of breastfeeding to most types of childhood cancers, except that wasn’t true. If you look at their data, they found protective effects for acute lymphoblastic leukemia, Hodgkin’s disease, and neuroblastoma (with a 9%, 24% , and 41% reduction in risk, respectively). Furthermore, their analysis for breastfeeding was only a comparison of “ever breastfed” versus “never”. As some of the other research has hopefully made clear, such a distinction fails to encompass the breastfeeding-cancer relationship; namely, that it is extended breastfeeding that has the largest impact on reducing cancer risks amongst children. But if the researchers who find these results don’t support them, how are parents supposed to know about and utilize this information? (I personally wonder if these scientists are towing a political line that doesn’t want to acknowledge these benefits because then they might actually have to support policies that allow for women to breastfeed instead of forcing them back to work too early or providing proper support in the form of lactation consultants and other specialists.)
A Cross-Cultural Story
While the rates of childhood cancer are 14.3 per 100,000 worldwide, according to the American Cancer Society, rates and types vary by location. It is the variety in types that interested me most and that I wanted to share. Based on the above evidence, it seems fair to say that breastfeeding holds its power to reduce risk on leukemias, lymphomas, and neuroblastomas. Data from the American Cancer Society’s Global Cancer Facts and Figures, 2nd Edition tells us that leukemia is the most common form of cancer in most parts of the world, and especially in Western nations, but is a rarity in Africa. In fact, if we examine the predominance of types of cancers in Europe versus Africa, a startling picture emerges. While leukemia, lymphoma, and neuroblastomas make up 49% of childhood cancer cases in North America, they make up 21% of cases in Africa (not including Burkitt lymphomas as they are linked to the Epstein-Barr virus and thus occur nearly exclusively in Africa and seem unrelated to other types of lymphomas). While a comparison of the rates of cancer is impossible as the diagnosis and treatment of cancer in Africa is qualitatively different than that in North America, it is interesting to note that on a continent where breastfeeding and extended breastfeeding are common—only 3.9% of babies receive no breastmilk in the first six months, 8.2% receive no breastmilk from 6 months to a year, and only 30.1% of infants do not breastfeed in the second year of life—the rates of childhood cancers that are affected by breastfeeding are much lower than in other areas of the world. Of course, none of this is causal and more research would need to be done to make firm conclusions, but combined with the evidence we see on childhood cancer and breastfeeding, it’s hard not to think something’s going on.
It’s difficult to argue against such data. It’s also difficult to understand why parents are not being given this information as it may be one of the strongest motivators to get parents to not only consider breastfeeding at all, but to continue to do so for longer periods than they currently do. After all, the fear, sadness, and horror that comes with witnessing a child who is fighting cancer is an unbelievable motivator for almost anything.
One thing that must be noted though is the implication for women who cannot breastfeed. It seems that in today’s society, any time you talk about the benefits of breastfeeding (or the harms caused by not breastfeeding) there are those people ready to jump down your throat to tell you how unfair it is as there are those who can’t breastfeed and you only serve to make them feel bad. You also make those who choose to artificial feed feel bad too. And I find that attitude to be a gross tragedy as it hurts everyone. By avoiding discussions about breastfeeding, we leave women who can’t breastfeed with both the belief that formula is just as good, when it clearly isn’t, and no impetus to push for better options for their children. Talking about the benefits of breastfeeding/risks of formula with respect to childhood cancer isn’t supposed to make moms who can’t breastfeed feel bad because their children are going to be at a higher risk of getting cancer, but it may have that effect. What it should do though is make these parents—hell, all parents—pissed that they’ve been fed the lie that formula is just as good as a substitute and in turn fight for greater access to milk banks and milk sharing services like Human Milk 4 Human Babies. Only when a large proportion of society accepts that consequences of not breastfeeding are unacceptable will we work to ensure that all children are given access to the benefits of breastmilk, regardless of what any single mom is capable of doing.
 Rosenblatt KA, Thomas DB, and the WHO collaborative study of neoplasia and steroid contraceptives. Prolonged Lactation and endometrial cancer. International Journal of Epidemiology (1995); 24: 499-503.
 Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and breastfeeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50302 women with breast cancer and 96973 women without the disease. Lancet (2002); 360: 187-95.
 Rosenblatt KA, Thomas DB, and the WHO collaborative study of neoplasia and steroid contraceptives. Lactation and the risk of epithelial ovarian cancer. International Journal of Epidemiology (1993); 22: 192-7.
 Brock KE, Berry G, Brinton LA, Kerr C, MacLennan R, Mock PA, & Shearman RP. Sexual, reproductive and contraceptive risk factors for carcinoma-in-situ of the uterine cervix in Sydney. The Medical Journal of Australia (1989); 150: 125-30.
 Lancashire RJ & Sorahan T. Breastfeeding and childhood cancer risks: OSCC data. British Journal of Cancer (2003); 88: 1035-1037.
 Shu X, Clemens J, Zheng W, Ying DM, Ji BT, & Jin F. Infant breastfeeding and the risk of childhood lymphoma and leukaemia. International Journal of Epidemiology (1995); 24: 27-32.
 Xu F, Lui X, Binns CW, Xiao C, Wu J, & Lee AH. A decade of change in breastfeeding in China’s far north-west. International Breastfeeding Journal (2006); 1: 22.
 Golding J, Paterson M, & Kinlen J. Factors associated with childhood cancer in a national cohort study. British Journal of Cancer (1990); 62: 304-308.
 Davis MK, Savitz DA, & Graubard AI. Infant feeding and childhood cancer. The Lancet (1988); 332: 365-368.
 Mathur GP, Gupta N, Mathur S, Gupta V, Pradhan S, et al. Breastfeeding and childhood cancer. Indian Pediatrics (1993); 30: 651-657.
 Roman E, Simpson J, Ansell P, Kinsey S, Mitchell CD, McKinney PA, et al. Childhood acute lymphoblastic leukemia and infections in the first year of life: a report from the United Kingdom childhood cancer study. American Journal of Epidemiology (2007); 165: 496-504.
 Duijts L, Jaddoe VWV, Hofman A, & Moll HA. Prolonged and exclusive breastfeeding reduces the risk of infectious diseases in infancy. Pediatrics 2010; 126: e18-e25.
 Shu XO, Linet MS, Steinbuch M, Wen WQ, Buckley JD, Neglia JP, et al. Breast-feeding and risk of childhood acute leukemia. Journal of the National Cancer Institute (1999); 91: 1765-1772.
 Kwan ML, Buffler PA, Abrams B, & Kiley VA. Breastfeeding and the risk of childhood leukemia: a meta-analysis. Public Health Reports (2004); 119: 521-535.
 Martin RM, Gunnell D, Owen CG, & Smith GD. Breast-feeding and childhood cancer: a systematic review with metaanalysis. International Journal of Cancer (2005); 117: 1020-1031.
 American Cancer Society. Global Cancer Facts & Figures, 2nd Edition. Atlanta: American Cancer Society; 2011
 http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002285/ (Accessed November 10, 2011)
 Lauer JA, Betran AP, Victora CG, de Onis M, & Barros AJD. Breastfeeding patterns and exposure to suboptimal breastfeeding among children in developing countries: review and analysis of nationally representative surveys. BMC Medicine (2004); 2: 26.