Lobules are the part of your breast that make milk (they’re actually glands). If you’ve given birth, you are sure to remember how your breasts changed over the course of your pregnancy…and then voila, like magic you are suddenly able to feed a tiny human.
OK. It’s not magic. We know why the breast change post-pregnancy–your lobules are now capable of making milk. There is a lot of change that your breasts undergo to be ready to produce milk (we can talk about that another time). But, when you are done breastfeeding, whether it’s on day one, or day 500, your breasts change again! This change is called postlactational involution.
You’re body gets the signal that it no longer needs to make milk, and all the cells that were supporting the process of milk-making, now turn on the self-destruct signal. That’s right, it sounds a bit harsh, but they know they are no longer need–and poof, they begin the process of clearing out so your breast goes back to a pre-pregnancy state (although most of us don’t seem to go back to that pre-pregnancy perkiness).
Sometimes, the cells in your breasts may get confused. This postlactational involution process is actually quite complicated and sometimes your cells make a mistake and can’t actually figure out how to complete the involution process. Women with incomplete involution are known to have an increased risk of developing breast cancer. Without a breast biopsy, your doctor can’t tell if you have undergone complete involution–so it’s a difficult risk factor to account for.
Although we don’t know all the reasons why, there is a 10-year window after giving birth, where your risk of breast cancer is increased. Development of breast cancer within this 10-year window is called, postpartum breast cancer.
During the involution process, there is a lot of inflammation due to all the “rearrangement” going on in the breast tissue. This inflammation may promote tumor growth in some circumstances. There is some evidence that breastfeeding longer than 6 months can be protective against some of these pro-inflammatory cellular changes. And we know every 12 months of breastfeeding reduces your risk of developing breast cancer. Just keep in mind, breast feeding is just one of many factors; just because you breastfed doesn’t mean you’re completely “protected.”
Finally, there is another type of involution that every woman goes through, regardless of whether she gave birth, or not. This is age-related lobular involution and typically starts around 40. The first type of involution we talked about involved the milk-producing-breasts shrinking back to normal. But, the age-related involution actually permanently replaces 75% or more of your lobules with collagen and fat. Studies have shown that women with complete involution are at lower risk of developing breast cancer.
During these lobular involution processes, your body is hard at work “remodeling” your breast tissue…and you’d never know it! Your body is pretty amazing, but occasionally “routine maintenance” can go off-course. You know your body best, trust your instincts and as always, stay up-to-date on your breast cancer screening.
- Basree, M.M., Shinde, N., Koivisto, C. et al. Abrupt involution induces inflammation, estrogenic signaling, and hyperplasia linking lack of breastfeeding with increased risk of breast cancer. Breast Cancer Res 21, 80 (2019).
- Tia R. Milanese, Lynn C. Hartmann, Thomas A. Sellers, Marlene H. Frost, Robert A. Vierkant, Shaun D. Maloney, V. Shane Pankratz, Amy C. Degnim, Celine M. Vachon, Carol A. Reynolds, Romayne A. Thompson, L. Joseph Melton, III, Ellen L. Goode, Daniel W. Visscher, Age-Related Lobular Involution and Risk of Breast Cancer, JNCI: Journal of the National Cancer Institute, 98, 22, 15 (2006)
- Maskarinec, G., Ju, D., Horio, D. et al. Involution of breast tissue and mammographic density. Breast Cancer Res 18, 128 (2016).