I’m really excited to join with other bloggers today to "write pink" and talk about breast cancer prevention. There are two excellent ways to reduce your risk of breast cancer, the first of which is almost completely unknown and the second of which is fairly well-known. Are you ready? They are (1) don't use hormonal contraception and (2) have babies!
How does hormonal contraception increase your risk of breast cancer?
When you use any type of hormonal contraception – oral pills, injections, implantations, vaginal rings and patches – you are increasing your exposure to estrogen. The more estrogen you are exposed to, the higher your risk of breast cancer. Even the “low-dose” pills are associated with greater risk. Also, remember the hullabaloo about hormone replacement therapy about 8 years ago? That was due to increased estrogen exposure, and is scarily similar to what happens with hormonal contraception.
It’s important to remember that estrogen itself isn’t evil or anything. The problem is when our bodies are getting excessive amounts of it. We’re being exposed to more and more of it, both in nature and in our immediate environment. Hyacynth also mentioned estrogen today and specifically noted the importance of avoiding hormonal contraception to avoid estrogen. She’s right!
The fact that hormonal contraception increases your risk of breast cancer is just that: a fact. Sometimes you will read that results are mixed, but really the science is clear. The World Health Organization has labeled oral contraceptives as a Group I carcinogen for breast cancer: it’s highly carcinogenic.
The Polycarp Institute concludes that women who take the pill before their first full-term pregnancy have at least a 40% increased risk of developing breast cancer. If that continues for four years or more, the risk is even higher. (The risk from Depo-Provera in particular is astoundingly large.) You can read a bit more about this here.
But I’ve heard the pill actually decreases your risk of ovarian cancer. So isn’t it just a draw?
Oral contraceptives do reduce the risk of ovarian and endometrial (aka uterine) cancer. However, they also increase the risk of cervical and liver cancer, in addition to the increased risk of breast cancer. What I think is most important to realize here is that more women get breast cancer than all of these other cancers combined. The NCI states that a U.S. woman’s lifetime risk of getting breast cancer is 1 in 8. Hormonal contraceptives increase your risk of what you were already more likely to get. (See Q-R.)
So if hormonal birth control is so dangerous, what’s a woman who needs to postpone pregnancy to do? Use Natural Family Planning! NFP comes in handy because it can also assist with achieving pregnancy, and as I explain below, full-term pregnancy decreases your risk of breast cancer.
How does having a baby reduce the risk of breast cancer?
I’m taking the following almost directly from here and here, and I encourage you to check out the Breast Cancer Prevention Institute for more information. The explanation can get a bit technical, but it’s really enlightening. I'll try to break it down here so it's easy to understand.
There are four types of lobules you can have in your breast, conveniently called Types 1, 2, 3, and 4. Type 1 lobules are where ductal breast cancers start (85% of breast cancers). Type 2 lobules are where lobular breast cancers start (12% of breast cancers.) Type 3 lobules are cancer resistant (you have them after weaning a child). Type 4 lobules are even more cancer resistant and contain milk (you have them while you’re breastfeeding). The lobules in your breast change due to pregnancy.
In the time between puberty and your first pregnancy, your breasts are almost entirely composed of Type 1 (75%) and Type 2 (25%) lobules. This time period is called the “susceptibility window” because that’s when your breast is most susceptible to forming cancer. That’s why earlier first full-term pregnancy (FFTP) lessens your risk of breast cancer - because this time span is shorter.
After you conceive, your body produces more estrogen and progesterone and your breasts get bigger and make more lobules. This means that there are more places for breast cancer to start. Also, the lobules are maturing from Type 1 to Type 2 by the end of the first trimester (still cancer-susceptible).
By the middle of the second trimester, your breast size has doubled and you have tons of lobules. By the end of the third trimester, 85% of the lobules are Type 4 - cancer resistant milk producers! That means only 15% of the lobules are susceptible to cancer.
At delivery, your breasts lobules have matured to be almost entirely Type 4. And that is why having a child reduces your long-term risk of breast cancer. Each additional birth reduces your risk by a further 10%.
Breastfeeding also reduces your risk of breast cancer. There are two reasons for this. First, your lobules remain Type 4 longer. Second, breastfeeding often causes anovulatory or missed periods, which means less exposure to estrogen. Risk decreases in proportion to the cumulative length of breastfeeding.
After you wean, your breasts get smaller again and the Type 4 lobules regress to Type 3 (which are also cancer-resistant). 85% of the lobules are Type 3 and there are still fewer places for cancers to start.
So to sum up, you start out with fewer but more cancer-susceptible lobules. Initially pregnancy increases the number of lobules but doesn't change the type (that’s an increased risk). But by the end of pregnancy, the type of lobules have changed to be cancer-resistant. The more babies you have and the longer you breastfeed, the lower your risk of breast cancer.
What if a pregnancy ends early?
If the baby is born between 32 and 37 weeks, the mother gets about 90% of the risk reduction of a full-term (40 week) pregnancy.
If a pregnancy ends before 32 weeks (either from very premature birth or induced abortion), a mother will have an increased risk of breast cancer.* This is because she will have more lobules but they haven’t changed types yet (meaning there are more places for cancer to start), and she has been exposed to high levels of estrogen throughout the beginning of pregnancy.
If a woman naturally miscarries during the first trimester, however, breast cancer risk does not increase. This is because these miscarriages are associated with low estrogen levels. (That’s why a woman who miscarries might not feel pregnant, because her breasts didn’t change and she wasn’t nauseous.)
For illustrations of the above scenarios, see here.
The moral of the story
Are there women out there who’ve breastfed several children and got breast cancer? Of course. Are there women out there who never take the pill and get breast cancer? I assume so. There is no single proven way to prevent breast cancer, but there are ways to reduce your risks of getting it. Two of the best ways to decrease your risk of breast cancer are to have babies and avoid hormonal contraception!
*The question of abortion causing breast cancer is a very politicized and hotly debated one (no surprise there). The Wikipedia article about it is fairly good and detailed. From my reading, though, I’ve gathered that the physical process which I’ve outlined here is actually not the part that’s debated. Since I’m less interested in talking about the abortion link and more interested in talking about the contraception link, I’m leaving it at that for this post.
For more information:
Breast Cancer: Its Link to Abortion and the Birth Control Pill (Read a pared down version of the final chapter here)
The Breast Cancer Prevention Institute
The Polycarp Research Institute