Breast Cancer Awareness Month: Endometriosis & Breast Cancer Risk
Research on endometriosis and breast cancer risk is mixed. The largest meta-analysis to date found only a very small (~4%) increase in relative risk, while other large studies found no association at all. Having endometriosis alone isn't a reason for extra mammograms or breast MRIs, screening should be based on age, family history, and personal risk factors. The one thing that doesn't change: always get new breast changes checked, even after a normal mammogram.
This Breast Cancer Awareness Month, it’s worth cutting through the noise on a question we hear often from PRM patients: if you have endometriosis, does that affect your risk for breast cancer? It’s a reasonable question, especially since both conditions are influenced by estrogen, and the honest answer is: the research is mixed.
Endometriosis and breast cancer are both classified as estrogen-related conditions, meaning estrogen plays a role in how tissue grows and behaves in both cases. Endometriosis involves tissue similar to the uterine lining growing outside the uterus, and that tissue responds to estrogen much like the uterine lining does. Breast tissue is also estrogen-sensitive, and estrogen exposure over a lifetime is a well-established factor in breast cancer risk generally.
Because both conditions share this estrogen connection, researchers have spent years investigating whether having one disease might signal something about risk for the other. That’s a legitimate scientific question, but a shared biological pathway doesn’t automatically mean one condition causes or significantly raises risk for the other.
Some studies have found a small statistical association between endometriosis and breast cancer. The largest and most comprehensive analysis to date, a 2021 systematic review and meta-analysis published in Human Reproduction Update that pooled data from 49 cohort and case-control studies, found what researchers described as “a very small association,” estimating roughly a 4% greater relative risk among people with endometriosis. To put that in context, researchers noted that applying this estimate to the general lifetime breast cancer risk (around 12.8%, per National Cancer Institute data) would move that number to roughly 13.3%, a small shift rather than a dramatic one.
Other research has found no connection at all. A 2023 retrospective cohort study out of Germany followed more than 15,000 patients with endometriosis, matched against an equal number of patients without the condition, and found no significant association with breast cancer over a 10-year period, even when researchers broke the data down by age group. Some genetic-level research has gone a step further: a Mendelian randomization study (a method that uses genetic data to test for likely causation rather than just correlation) found no causal relationship between endometriosis and breast cancer at all, and one such study even pointed toward a very slightly protective association.
It’s worth understanding why studies on this topic don’t all agree, because that inconsistency is itself informative. Researchers conducting these meta-analyses have pointed to a few recurring issues:
Taken together, this is what “mixed research” actually looks like in practice: a handful of studies pointing toward a small statistical association, several large, well-designed studies finding none at all, and genetic-level research suggesting no causal link. Even among the studies that do find an association, researchers are consistently careful to note that a small statistical correlation is not the same thing as proof of causation. Having endometriosis doesn’t mean endometriosis is actively driving breast cancer risk in any individual patient.
Here’s the practical takeaway: an endometriosis diagnosis alone is not, by itself, a reason to pursue additional mammograms or breast MRIs beyond standard guidelines.
Breast cancer screening decisions should continue to be based on the factors that are already well-established to matter:
If you have endometriosis and are unsure what screening schedule makes sense for you, that’s a conversation worth having directly with your provider, one that factors in your whole health picture, not just one diagnosis considered in isolation.
Regardless of what the research on endometriosis and breast cancer eventually settles on, one piece of advice doesn’t change: get any new breast changes checked, even after a normal mammogram.
A mammogram is a snapshot in time, not a guarantee about the future. New lumps, changes in skin texture, nipple changes, or persistent, localized pain are always worth bringing to a provider’s attention, regardless of when your last screening was, what it showed, or whether you have an endometriosis diagnosis at all.
Does having endometriosis mean I need a breast MRI instead of a regular mammogram? Not based on an endometriosis diagnosis alone. Breast MRI is typically reserved for patients with significantly elevated risk factors, like a known genetic mutation or strong family history, not a general endometriosis diagnosis.
Should I start breast cancer screening earlier because I have endometriosis? Current evidence doesn’t support changing your screening start age based on endometriosis alone. Screening age recommendations are driven by broader risk factors like family history and genetics.
If my family has a history of breast cancer and I also have endometriosis, does that add up to higher risk? Family history remains the more significant factor to discuss with your provider. Endometriosis isn’t established as adding meaningful additional risk on top of a genuine family history, but it’s still worth mentioning your full history during that conversation.
Why do some studies disagree about this topic? Different studies define and confirm endometriosis differently, follow patients for different lengths of time, and don’t always account for the same confounding factors, which is part of why results vary across the research.
Endometriosis research is still evolving, and it’s completely normal to have questions about what a diagnosis means for the rest of your health. When it comes to breast cancer specifically, the evidence doesn’t support treating endometriosis as a major risk factor requiring extra screening, but it does support staying attentive to your body and having an informed, whole-picture conversation with your provider about what’s right for you.
Not based on an endometriosis diagnosis alone. Breast MRI is typically reserved for patients with significantly elevated risk factors, like a known genetic mutation or strong family history, not a general endometriosis diagnosis.
Current evidence doesn’t support changing your screening start age based on endometriosis alone. Screening age recommendations are driven by broader risk factors like family history and genetics.
Family history remains the more significant factor to discuss with your provider. Endometriosis isn’t established as adding meaningful additional risk on top of a genuine family history, but it’s still worth mentioning your full history during that conversation.
Different studies define and confirm endometriosis differently, follow patients for different lengths of time, and don’t always account for the same confounding factors, which is part of why results vary across the research.
