One of the most frightening things for women with breast cancer is that it can come back years—or even decades—after successful treatment. The return of breast cancer also poses challenges for medical treatments because researchers don't know how cancer hides in the body.
Many patients finish treatment believing the cancer is gone for good, only to discover their breast cancer has returned.
Now, researchers believe they may have found an important piece of the puzzle.
A new study published in Bone Research reveals how breast cancer cells hide from detection only to suddenly become active again.
Cancer Cells Can Go Into "Sleep Mode"
After a breast tumor is treated, a small number of cancer cells can sometimes break away and travel to the bone marrow. This is where they lurk until they mysteriously wake up.
Instead of growing into new tumors right away, these cells can enter a dormant state—essentially going to sleep.
While dormant, the cells stop dividing and remain inactive. Because many cancer treatments target fast-growing cells, these sleeping cancer cells can often escape treatment.
The problem is that they don't always stay asleep.
Months, years, or even decades later, some of these cells can begin growing again, leading to new tumors in the bones or other parts of the body.
How Do These Cells Stay Hidden?
Researchers discovered that breast cancer cells may survive by pretending to be something they're not.
Inside the bone marrow are special areas that help protect healthy stem cells, which are responsible for producing new blood cells and repairing tissues.
The study found that dormant breast cancer cells appear to mimic some of the same characteristics as these healthy stem cells. By doing so, they gain access to the bone marrow's protective environment and can remain hidden for long periods.
In other words, the cancer cells may be using the body's own survival systems to protect themselves. We've always know that cancer is sneaky in ways that until now, defied medical explanation.
One Protein Stood Out
The researchers focused on two proteins called Notch1 and Notch2, which help cells communicate and respond to their surroundings.
What they found was surprising.
While both proteins were present in breast cancer cells, Notch2 appeared to play a much bigger role in helping the cells remain undetected.
Cells with high levels of Notch2 divided much more slowly—a hallmark of dormant cancer cells. Cells with higher levels of Notch1 did not show the same behavior.
This suggests that Notch2 may act like a switch that helps breast cancer cells enter and maintain their sleeping state.
Cancer Cells Start Acting Like Stem Cells
These genes help stem cells survive inside the bone marrow, and breast cancer cells appear to be using the same tools.
In experiments with mice, cells carrying these stem cell-like traits produced fewer and smaller tumors, further supporting the idea that they were remaining dormant rather than actively spreading.
A Survival System Helps Them Endure
The researchers also found evidence that dormant cancer cells activate special stress-response systems that help them survive even when they're under attack from lack of nutrients, low oxygen levels, or other environmental stresses.
One molecule that caught the researchers' attention was CD177.
Cells with high levels of CD177 were more likely to be dormant and less likely to divide rapidly. Interestingly, patients with higher levels of this marker also tended to have better outcomes.
This suggests CD177 could one day help doctors identify dormant cancer cells and better predict a patient's risk of recurrence.
Why This Discovery Matters
The findings could have important implications for the future of breast cancer treatment.
Most current therapies focus on destroying actively growing cancer cells. Dormant cells are much harder to target because they remain hidden and inactive. The goal could be to include breast cancer treatments that also get rid of sleeping, or dormant cells, or immobilize them forever.
If successful, these approaches could help reduce the risk of breast cancer returning years after treatment.
The Bottom Line
Scientists have uncovered new clues about how breast cancer cells can hide in the bone marrow for years before causing a relapse. The study suggests these cells survive by acting like healthy stem cells and taking advantage of the bone marrow's natural protective environment.
The discovery of key players such as Notch2, CXCR4, and CD177 could eventually lead to new therapies aimed at preventing breast cancer recurrence—offering hope to millions of survivors worldwide.
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