Pregnancy changes a woman’s body in many ways. One of the most visible of these changes is that of the breasts. During pregnancy, a woman’s breasts will swell and become more sensitive to touch. Following birth, a mother then begins to lactate. However, not all breast changes are as welcome as the rest. It’s been shown that the post-birth environment is ideal for the growth of cancerous tumors. Fortunately, a new study has found one of the main reasons for this occurrence, and possibly revealed a way to prevent it.

Postpartum breasts carry a greater risk for breast cancer than breasts of women who have never given birth. According to the American Cancer Society, more than 232,670 women are diagnosed with breast cancer each year. According to The Denver Post, of these 232,670 women, about 12 percent are defined as postpartum, meaning that they have given birth within the last five years. On top of these figures, women diagnosed with breast cancer within five years of giving birth are also three times more likely to experience a recurrence than those who are not classified as postpartum.

"Obviously, women can't stop giving birth," Virginia Borges, an oncologist and director of the Young Women's Breast Cancer Translational Program at the University Of Colorado Cancer Center, told The Denver Post. "Having children is a part of life. But millions of women give birth every year, and a percentage of them are getting breast cancer...”

Not only is the environment of postpartum breasts ideal for the development of breast cancer, but often this cancer tends to be more aggressive. According to a press release, women who are diagnosed with postpartum breast cancer have a decreased disease survival time when compared to women who have never given birth. A new study, now published in the Journal of Clinical Investigation, may have uncovered the reason for this.

The team of researchers from Vanderbilt University in Tennessee found that dying tumor cells in postpartum breast tissue of mice promoted the mestastic disease, or the spread of the cancer from one organ to another. This is caused by the drastic changes that the breast undergoes in order to produce milk. As lactation cells are formed, older cells die. These cell deaths trigger the secretion of anti-inflammatory cytokins, which promote wound healing and clearance of dead cells.

What was most intriguing, however, was what happened when this process goes wrong. “Mice lacking a receptor on macrophages that is required for the clearance of dying cells did not develop metastatic disease,” the press release explained. This suppression of the natural “wound-healing” process prevented the cancerous tumors from further spreading and thus becoming more dangerous. Although only in the beginning phases, the researchers hope that these findings can one day be used to help prevent the severity of breast cancer in postpartum women.

Source: Cook R et al. Journal of Clinical Investigation. 2014.