Mirena IUD/breast cancer

I had a mirena IUD from about 2010-2014. I had it taken out and did a few cycles of egg freezing. I went to go get a new hormonal IUD (not Mirena but Liletta) in summer 2018. The day I got it inserted, the gyn found the lump in my breast that turned out to be breast cancer.

For me, getting that new IUD was the only reason my cancer was found so early. I don't believe the Mirena had anything to do with the cancer. Medicine doesn't really understand the role that progesterone plays in ER+/PR+ cancer, and they are just playing better safe than story. There is a lot of evidence that taking estrogen supplementing hormones increases risk. Almost none for progesterone. In fact, they are now speculating that progesterone actually helps slow down the spread of estrogen based tumors, and that is why being both ER+ *and* PR+ seems to have better outcomes than ER+ alone. They are at the very early stages (non-human) of studying whether progesterone *supplementation* might have a positive effect for slowing cancer growth. (This could well not apply to hormonal IUDs in the end, because they are based on synthetic progesterone, but it still shows - to me - that progesterone shouldn't be treated the same as estrogen in a knee-jerk way).

There were multiple studies that didn't find a link between breast cancer and hormonal IUDs. Only one study did find a link to increased recurrence rates for women who already had breast cancer, but it wasn't well designed for studying the impact of the hormonal IUD specifically versus the impact of long nulliparous-ness, and the tiny increase in risk of breast cancer it showed was more than completely balanced out by the reduction in the risk of ovarian cancer.

My gyn and all my oncologists wanted me to get the IUD out. Like a knee jerking. I resisted. I love the effective birth control and the lack of periods. I delayed until I could meet with the medical oncologist. She admitted to me that she was not counseling me to take the IUD out based on any specific studies or evidence about the impact of hormonal IUDs, but just on the general principal of removing exogenous hormones. She said she didn't know about any studies involving hormonal IUDs. Well - I knew about a couple of studies involving hormonal IUDs, so that tells me she isn't very informed on the subject, just following that knee-jerk trend. She consulted with an oncologist gynecologist at my cancer center, who confirmed to her that the IUD would not increase the risk for blood clots the way an estrogen-based birth control would (which is a big concern with tamoxifen), and also told her that she (the gyn) had had a few patients over the years who'd used hormonal IUDs, and done fine. At that point, the medical oncologist told me that she would make a note in my file that she'd advised me to remove the IUD and been advised of the risks (unnamed, non-evidence-based risks....) and I had chosen not to, and we could just close the subject.

So I am keeping my Liletta IUD. I appreciate the protection against ovarian cancer and also the protection against thickening uterine lining, which is a known side effect of tamoxifen. I love the reliable birth control, and the lack of periods.

It is very tempting to find something to blame breast cancer on. But I don't think the Mirena is it. For me, maybe it's easier, because my mother and my grandmother both had breast cancer without ever having spent time on any kind of hormonal birth control. So it doesn't seem to me that I need to blame the birth control. If anything, I think the hormones I took for the egg freezing are a much more likely culprit.

Mirena user for almost 10 years, the second 5 years after age 40. Diagnosed with ILC in the two months following removal of the Mirena (2nd user). I absolutely believe but cannot prove that Mirena caused weight gain and that the progestin stimulated proliferation of breast tissue and caused breast cancer. There is at least one recent internationally valid study in Acta Ontologica indicating significant increased BC risk (say 19%) with levonogestrel usage, with risk higher for those using it for more than 5 years.

The mechanism for progestins being carcinogenic is as follows. (I am not a doctor, but I am not unintelligent either.) The progestin replaces your body's natural progesterone, but unlike natural progesterone, it does not act completely like natural progesterone and it does not balance out or down-regulate your estrogen. Unopposed estrogen is a known carcinogen and acknowledged as such by IARC. Massive amounts of estrogen can of course also be produced by your own body fat. Either way, therefore, you become estrogen dominant and are at increased risk of breast cancer.