In mice, pregnancy appears to slow the accumulation of suspicious breast cells
Frankenstein’s cellular monster has breathed new life into an old breast cancer mystery.
For decades, scientists have known that early pregnancy somehow reduces the risk of breast cancer as women age. No one has said how, but a group of strange breast cells could help solve the case. In female mice, these cells accumulate over time — unless an animal was pregnant, scientists report January 21 Natural communications.
This suggests that pregnancy blocks accumulation, and that might be a good thing. The cells have undergone an identity crisis that could drive cancer progression, says Shaheen Sikandar, a cancer and stem cell biologist at the University of California, Santa Cruz. If the cells actually do it pushing tissues toward diseasepreventing their buildup could also prevent breast cancer, she says. “We are trying to understand why these cells appear and if there is a way to stop them.”
For women, giving birth before your 20s may reduce your lifetime risk of breast cancer, although estimates vary. A few clues to the phenomenon come from young mice, whose mammary tissues undergo molecular changes after pregnancy. But no one had a good idea of what happened in older animals, once the pregnancy-protective effect occurred, Sikandar says.
His team compared pregnant mice with those that were not, and examined the two groups at different ages – up to 18 months, the equivalent of 55 to 65 years in humans. Researchers probed breast tissue using a technique that allowed them to identify cells and see what each was doing.
In aged mice that were not pregnant, the team discovered cells with particular characteristics. They were hybrids, for example. Instead of being either of the two main types of breast cells, the hybrid cells were a mix of the two. This kind of identity change may be a key driver of canceranother team of researchers studying lung tumors reported in a separate study published Jan. 21 in Nature.
The hybrid cells discovered by Sikandar’s team produce an inflammatory molecule called IL33. Injected into young mice, IL33 appears to age breast tissue, causing it to form hybrid cells, like those in older, never-pregnant mice, the researchers found. It’s possible that early pregnancy offers a cellular reset, stopping the buildup of these irregular cells, Sikandar says. But many questions remain.
Mice and humans are very different animals, so it’s unclear whether the team’s observations will hold in humans, says Mark LaBarge, a breast cancer researcher at City of Hope in Duarte, California. It is also too early to say whether these hybrid cells are a driver of cancer. Sikandar agrees. “We think they’re bad,” she said. “They show all the signs of being evil.” But the team is currently conducting experiments to find out.
For LaBarge, the study sparked “cautious optimism and curiosity.” By examining mice, Sikandar’s team discovered a “really interesting population of cells,” he says, and that’s reason to do more research.
