When does breast cancer start? New study says its when you're asleep

FRESNO, Calif. (KFSN) -- About one in every eight women will develop breast cancer during her life.

"I just, I felt something and I thought, huh, it was real tiny, but it just felt different," patient Kristen Lyons says. "I was never one for self-examination, and that was a big mistake."

When breast cancer is found early, it's highly treatable. But if it's spread, "metastasized", the prognosis isn't so good.

"So, we understand metastatic breast cancer, it's not curable," Oncologist Sara Hurvitz says.

Scientists know metastasis happens when circulating cancer cells break away from the original tumor and travel in the body via blood vessels.

Until now, researchers assumed tumors released cells continuously and haven't known much about when tumors spread.

In a new study researchers examined mice and female cancer patients.

They found circulating cells that later form metastases mainly arise during sleep. In other words: when a person or animal is asleep, the tumor seems to "wake up."

Cells that leave a tumor at night also seem to divide more quickly compared to cells that exit in the daytime.

Researchers say this isn't just an interesting finding, it could help improve the way breast cancer is diagnosed and treated in the future.

For instance, the next step is to see if giving patients therapies at different times of the day has an effect on outcomes.

New information that could change how doctors treat breast cancer.