Postpartum Breast Cancer Prevention
The deadliest breast cancers spike postpartum, and evidence suggests ways to possibly lower the risk -- but no one's telling moms about the problem or possible solutions
Once upon a time, there was a good woman who followed the rules: She had babies, breastfed them, and so earned lifelong protection from breast cancer. If more women made her choices, they’d get her health outcome. The end.
Not.
In reality, there’s a huge postpartum spike in breast cancer risk. Postpartum breast cancers are far more lethal than other types, because they metastasize at about 2-5x higher rates (see, e.g., Nichols et al 2018, Callihan et al 2013, and Goddard et al 2019).
Metastases kill. So typical breast cancer rate figures need to separate out the subgroup of cancers that are postpartum cases, because this is a meaningfully different subset.
What’s with the risk spike? Oregon Health & Science University Professor of Cell, Developmental and Cancer Biology Pepper Schedin and colleagues suggest it’s because cancer cells seed neighboring lymphatic tissue along remodeling latticework as breast tissue does strike on the lactation set, rapidly tearing down what the body built during pregnancy and breastfeeding — and rebuilding anew. This process creates a kind of molecular superhighway for rogue cells to travel where they’re more likely to metastasize from later. You can’t avoid it by breastfeeding or bottle-feeding; the postpartum body runs the lactation and, eventually, weaning programs no matter what you do (unless it doesn’t, but lactation failure is another story). But this is relatively recent research and we still have a lot to learn.
In any event, it takes this lethal breast cancer risk spike decades to attenuate. So, far from decreasing breast cancer risk — as the conventional wisdom says — something about the conjoined processes of pregnancy, lactation, and weaning seems to massively increase breast cancer risk for a long time. Yet, no one tells new moms that the postpartum period looks like a sensitive period for future breast cancer risk.
What New Moms Aren’t Told
What you do and don’t do during sensitive developmental periods (in utero-early infancy, adolescence, pregnancy/postpartum) can have outsize consequences for future health. So taking special care of your health postpartum may make a life or death difference for moms.
We could have better-quality evidence on what this means. But that doesn’t mean the current status quo — effectively zero clinical translation of what the imperfect evidence we do have, suggests — is fine.
Here’s what current evidence suggests.
Do
Everyone knows it, but changing your lifestyle is hard. Especially when you’re sleep-deprived and moving more is the last thing you feel like doing. I have no solutions here, only sympathy. And hey, maybe fussy baby bouncy-walking counts?
Eat well
As I wrote previously, there’s an extensive literature on diet and breast cancer risk. On one hand, cancer-diet associations are often flimsy (Shoenfeld and Ioannidis 2013). On the other hand, there’s suggestive evidence on a number of generally healthy foods that probably can’t hurt you anyway, like citrus, cruciferous vegetables, green tea, and fish oil. And then there are some big potential effects for soy.
Harvard’s soy page offers a good breakdown of how much of what soy foods contains how many isoflavones (the active component for our purposes), along with a nice summary of research on breast cancer and soy. This includes highlights from the Shanghai Women’s Health Study suggesting massive possible protective effects of a soy-heavy diet.
Some research suggests soy doesn’t only decrease breast cancer risk, but may also reduce the risks of recurrence and death in breast cancer patients; but the jury is out, with some specialists recommending breast cancer patients avoid soy instead.
Some research suggests timing matters, and eating lots of soy in adolescence is most impactful. Pregnancy and postpartum are similarly sensitive developmental windows where we might expect diet to matter more for breast cancer risk because of tissue remodeling. So if soy isn’t your thing, you don’t have to snack on it forever.
Have Another Cup
Some research suggests a weak inverse relationship between relatively high caffeine consumption and breast cancer, as well as a stronger inverse relationship between caffeine and colorectal cancers. One possible causal mechanism has to do with caffeine reducing serum folate levels. Folic acid increases cancer risks, and reproductive-aged women are generally told to take it to prevent birth defects without being told it may specifically increase their breast cancer death risk. If mitigating that possible risk may be as easy as having another cup of coffee or tea, and you like it, go for it. (But yes, there are two conditionals there. Sorry; clickbait, this ain’t.)
Ease Your Pain
Non-steroidal anti-inflammatories like ibuprofen and aspirin may lower cancer risks. The mechanism is thought to be inhibition of the COX-2 inflammatory pathway.
Their main risks have to do with possible GI bleeding, and seem low in general. You can also take something like pantoprazole with them to protect the stomach, if you’re going to be taking them daily for weeks or months at a time.
It would be great if we had randomized controlled trial data on what dose of ibuprofen new moms could take how often to lower postpartum breast cancer risk (if it works). We don’t. So probably it just makes sense to treat pain with painkillers as appropriate. But you might as well know that the “this could prevent cancer” framing is more evidence-based than the “drug-free is the way to be” one in this case.
Sleep
Sleep deprivation causes inflammatory changes. Babies cause sleep deprivation. So if you can get someone else to take a night shift, do it. It doesn’t just feel good. It feels good because it’s healthy. The modern, Western one mama/one baby norm is ahistorical crap: Human beings are cooperative breeders, evolved as a species to raise our very expensive and slow-maturing young by getting a lot of help from a lot of sources in the process.
Don’t
You know this already. Don’t drink alcohol.
You know this already, too. Don’t smoke.
Feel pressured to conform to the “breast is best” norm. There is a huge breast cancer section in my long-abandoned breastfeeding book, and I can’t face it today in Overleaf. But basically, the evidence doesn’t establish that breastfeeding reduces breast cancer risk. One reason is that any observed link could causally result from different biological lactation abilities rather than different breastfeeding behaviors. However, there is suggestive evidence that weaning gradually instead of suddenly is safer as it triggers less inflammation; having oversupply (far from being a boon) could be risky (as it triggers weaning continually, and this is a risky window); and tissue injury (e.g., mastitis) could be risky, too.
Preventing Breast Cancer Deaths: Rethinking Mammography
I’m still wondering how one would go about doing a net cost-benefits assessment for mammography as a case study of a mass screening for a low-prevalence problem. Do women give or get other important information in the screening process (i.e., are there side benefits to account for here)? Are there practically meaningful risks of harm from the radiation, compression, follow-up needle biopsies or surgeries, or other aspects of it — especially when it’s iterative? Or is it just really the classification test mechanism that we care about? How do we figure in perverse incentives and common cognitive distortions? And, most importantly, how do we calculate resource (re)allocation costs? If there are huge possible preventive medicine wins here, but we don’t know what they are yet, then how can I actually help anyone by estimating the uncertainties?
More Information, Less Myth-Based Medicine
Pregnancy is a trip. A hormonal, psychedelic, life-creating, brain-and-body-transforming journey. It carries great creative and healing power… And also risks. One of the low-probability, high-impact ones is postpartum breast cancer.
The absolute risk of postpartum breast cancer is quite small. I corrected denominator and decimal mistakes in the medical literature, estimating its prevalence at around 1.9 in 10,000 (.0192%) annually. (Previous estimates were an order of magnitude greater.)
Still, we have decent evidence for ways to potentially reduce that risk and probably not do harm trying. We should be sharing that information with every new mom. We should be researching it more. And we should be asking harder questions about where our prevention money goes — and what real healthcare looks like.