Posted: 2:44 p.m. Friday, Nov. 25, 2016
…The Texas A&M University team knew that some stem cells tended to be “recruited” into growing breast cancer tumors. The researchers figured that if they could discover why, they could use a stem cell “like a missile that you load up with something” that kills the cancer. Yet time after time in the experiments, the missiles kept disappearing. They couldn’t figure out why.
After unsuccessful trials — dating as far back as 2010 — plus the advice of researchers who mentioned an often-overlooked phenomenon of “cannibal” cells, Bartosh and his colleagues realized their experiments hadn’t been a failure.
According to a paper published in the Proceedings of the National Academy of Sciences, they might have stumbled upon the reason why breast cancer recurs so often, and why it often returns from dormancy in a form more resistant to treatment.
“We overlooked (the implications of the experiment) for years,” Bartosh told the American-Statesman. “It was one of those situations that was disappointing because your system isn’t working, and then you do a 180 and there’s excitement in the room about what you’ve found.”
What scientists found won’t yield a new treatment anytime soon. But the research appears to have uncovered a key insight into what happens when breast cancer becomes dormant. What the cancer cells do during that dormancy has vexed researchers for decades.
Survivors have at least a five-year window when relapse is most common, and they might worry for the rest of their lives about whether the disease will again try to ravage their bodies. If the cancer hasn’t spread to the lymph nodes, the chance of a recurrence within five years is about 6 percent, according to statistics from the Susan G. Komen breast cancer awareness organization. If it has spread to the lymph nodes, the odds of recurrence after radiation therapy is about 6 percent, with the odds rising among those who opt for other forms of treatment to 23 percent.
“Knowing what causes some breast cancer cells to become dormant, and then reawaken later, is key to understanding and stopping breast cancer metastasis,” said Joni Avery, a Komen spokeswoman.
At their lab, near Scott & White Memorial Hospital in Temple, Bartosh and his colleagues examined how bone marrow stem cells — chosen for the study because they are common in the body — interact with breast cancer. The disappearance of those stem cells frustrated the researchers. Others had previously discovered evidence of a cancer cell eating another kind of cell. But, Bartosh said, the phenomenon rarely draws attention and didn’t come up as a possibility until his team had shared their frustrations over what seemed to be bizarre experimental failures with colleagues elsewhere.
“Cell cannibalism is just something you don’t think about,” he said.
Once that idea was on the table, the researchers found that the cancer cells were, indeed, eating the stem cells. Afterward, the cancer cells got “sleepy.” But, contrary to the more popular theory, they didn’t go dormant. They weren’t proliferating, but they were sending signals to one another.
“It really appears that the growth-arrested cells weren’t really sleepy. They seem to be quite active,” Bartosh said.
With so few of those cells, they were difficult to detect — the kind of difficulty faced by modern screening methods. Those cancer cells also became more resistant to chemotherapy. When they awoke, they were harder to kill off.
The process occurred in the breast tissue of mice tested at the lab. But Bartosh is careful to note that the research hasn’t proved definitely that the same process is happening in human bodies. Likewise, he and his research team aren’t certain why the cancer cells eat the stem cells or what exactly happens to the cancer cells that causes them to go dormant while making them more resistant to treatment.
“There are some wild ideas about what’s going on,” he said.
Experts often encourage the public to consider cancer not one disease, but many diseases with some similar characteristics. That line of thinking appears to apply to the Texas A&M findings. Bartosh and his colleagues have tested the interaction of stem cells with a half-dozen types of cancer, he said. Melanoma and pancreatic cancer are among those that appear to react to the stem cells the way that breast cancer does. Ovarian cancer is among the cancers that appear not to, Bartosh said.