Tuesday, January 13, 2009

Breast Cancer Part II: Breastfeeding after Breast Cancer

A "Before and After" theme: Breast Cancer Part I discussed how breastfeeding and other lifestyle changes may help protect women from breast cancer. Part II will discuss breastfeeding after breast cancer.

The idea for this post came from an interesting thread on one my nutrition listservs regarding cancer diagnosis and later breastfeeding. Can and should a woman breastfeed if she previously had breast cancer? Would it be protective, harmful, or neutral? This is an important question considering that 3% of all diagnosed breast cancers occur in pregnant or lactating women.

I remembered this article about pregnancy and cancer in the NYT.
I will quote the relevant text:

"Can hormonal changes during pregnancy cause cancer? Evidence suggests that, at the very least, pregnancy hormones can cause pre-existing abnormal breast cells or growths to develop quickly and aggressively. In addition, pregnancy, it seems, changes the way the body handles the threat of cancer: During a healthy person’s lifetime, cells undergo changes that may or may not turn them into cancer. “Cells may be on the verge of becoming evil cells, then typically go back to being normal,” says Dr. V. K. Gadi, an oncologist at the Fred Hutchinson Cancer Research Center in Seattle. “But during pregnancy, there’s a surge of hormones that help promote certain types of breast cancer. It’s a highly estrogenic environment.” Meanwhile, the woman’s immune system is learning to tolerate the fetus, which is in many ways like a transplanted organ. “Essentially, the immune system is dampened to protect the fetus,” Gadi says. “Cancer cells take advantage of this opportunity where the immune system is backing off from its normal processes. They’re emboldened. And that’s the perfect storm.” The effects of this “perfect storm” appear to linger during the postpartum period. While pregnancy lowers a woman’s lifetime chances of developing breast cancer, her risk is actually heightened in the 2 to 10 years following childbirth. Moreover, if a woman has been pregnant within the last two years and develops breast cancer, she is twice as likely to die from the disease."

Although this is a controversial topic that is seemingly simplified in this quote, I was left wondering if this lingering postpartum "perfect storm" would be diminished by the additional hormones from breastfeeding. Breastfeeding would thus reduce the risk of breast cancer during the postpartum period. I propose my theory below and I would love to hear your comments!

A little Biology 101
After the placenta is delivered, progesterone and estrogen decrease dramatically. The receptor sites on the cells of the milk ducts are then open to receive prolactin. Prolactin increases each time breastfeeding occurs and ensures an adequate milk supply. However, if breastfeeding does not occur frequently enough, or a piece of placenta remains, or birth control pills containing progesterone are introduced prior to 6 weeks postpartum, then prolactin levels will not increase. This is because the cells will always prefer and accept the progesterone. Low prolactin levels and high progesterone levels lead to a decreased milk supply.

What does this have to do with breast cancer?
In hormone-receptive breast cancer, more cancers are progesterone-receptor positive, rather than progesterone-receptor negative. So getting rid of the progesterone and replacing it with prolactin would seem to be protective against breast cancer. However, this theory is complicated by the fact that prolactin receptor sites are also found on a majority breast cancers and that prolactin is shown to promote cancer growth.

Let us review what we know:
We know that breastfeeding protects against breast cancer (see Part I). We also know that there is no evidence that breastfeeding increases breast cancer recurrence. We know that breast cancer can have receptor sites for progesterone and prolactin. And we know that progesterone receptors can be involved in turning on breast cancer cell growth, while prolactin promotes breast cancer cell growth.

The Theory
There are many theories on why breastfeeding protects against breast cancer: it reduces the number of menses cycles and ovulation, physical changes in the breast during breastfeeding, low DNA synthesis during breastfeeding, or elimination of carcinogens through milk ducts.

I understand I am venturing outside of my expertise, but here is what I am thinking: The longer you breastfeed for, the longer your body remains in a state of elevated prolactin and decreased progesterone. This prevents breast cancer cells from turning on, negating the fact that prolactin can cause cancer growth because there are no cancer cells (hopefully). This idea is supported by the fact that the research shows greater protection from breast cancer with longer periods of breastfeeding (12 months and on). And it would also make sense that women who have previously had breast cancer would benefit from breastfeeding due to this progesterone suppression.

To bring Part I and Part II together:
Breastfeed to protect against breast cancer and breastfeed after you recover from breast cancer, but maybe not while you have breast cancer.

These guidelines are actually easy to follow since most women will not be allowed to breastfeed during cancer due to toxic levels of chemotherapeutic drugs and radiation. Traditionaly women were told to"pump and dump" their milk to maintain their supply and then continue breastfeeding after treatment. However, I am not sure how wise that advise is based on the aforementioned theory.

If you are a breast cancer survivor who became pregnant and you would like to breastfeed, please make sure to find youself a good lactation consultant. If you had breast surgery or radiation, there may be damage to the affected breast resulting in low milk supply to the affected breast depending on the extent of treatment. But you won't know until you try. Many breast cancer survivors have gone on to breastfeed from both breasts very succesfully and this has been documented in the literature. I would love to hear your stories!

For everyone reading this post who has healthy breasts, realize the gifts that you were given and put them to good breastfeeding use (besides the good uses they have served you until now). And please become familar with how your breasts look and feel so you can detect cancer early, before you get pregnant.

Related post: Breast Cancer Part I: Breast Cancer Prevention

1 comment:

  1. Hi
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