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does breast cancer sometimes recur after treatment? A new study suggests that
in part, the answer may lie in the effect of adjuvant hormone therapy on some
cancer cells.
Scientists delve deeper into the effects of hormone therapy on cancer cells, hoping to find out more about what drives recurrence.
"For a long time scientists have debated
whether hormone therapies — which are a very effective treatment and save
millions of lives — work by killing breast cancer cells,
or whether the drugs flip them into a dormant 'sleeper' state," says Luca
Magnani, who is a principal research fellow in the Faculty of Medicine at
Imperial College London in the United Kingdom.
"This is an important question as
hormone treatments are used on the majority of breast cancers," he notes.
Magnani and colleagues from Imperial College
London, the University of Milan in Italy, and Yonsei University College of
Medicine in Seoul, South Korea — among other academic institutions — have
recently delved into this debate, studying approximately 50,000 single cells of
human breast cancer.
In their study, the researchers looked at the
effect of adjuvant endocrine therapy — a type of hormone therapy — on these
different breast cancer cells.
"Our findings suggest the drugs may
actually kill some cells and switch others into this sleeper state. If we can
unlock the secrets of these dormant cells, we may be able to find a way of
preventing cancer coming back,
either by holding the cells in permanent sleep mode or by waking them up and
killing them," explains Magnani.
The researchers' findings now appear in the
journal Nature Communications.
Findings give rise to more
questions
Doctors usually recommend hormone therapies for
the treatment of estrogen receptor-positive
breast cancers, in which the cancer cells grow and spread by interacting with a
hormone called estrogen.
The American Cancer Society note that these
make up the majority — about two-thirds — of breast cancer cases.
Typically, a course of hormone therapy
follows surgery for tumor removal,
and while this strategy is successful in many cases, some people experience a
relapse. This can lead to metastasis — a state in which cancer cells spread
throughout the body, making it more difficult for doctors to spot and treat.
"This strategy significantly delays
clinical relapse but does not abrogate it completely, as about 3% of the
patients each year come back with overt relapse, inevitably leading to further
metastatic development," the researchers write in their study paper.
In the study,
Magnani and colleagues found that while adjuvant hormone therapy did indeed
kill most of the cancer cells they exposed to it, it only sent some cancer
cells into a dormant state.
This state can be temporary, meaning that
there is a possibility these cancer cells will later "awaken,"
leading to the formation of new tumors.
"These sleeper cells seem to be an
intermediate stage to the cells becoming resistant to the cancer drugs,"
hypothesizes study co-author Dr. Iros Barozzi. "The findings also suggest
the drugs actually trigger the cancer cells to enter this sleeper state,"
Dr. Barozzi adds.
Moreover, the researchers' "experiments
suggest these sleeper cells are more likely to travel around the body,"
according to another study co-author, Dr. Sung Pil Hong. Yet how and why some
cancer cells become dormant, and what factors may contribute to their awakening
remain a mystery.
"They
[the sleeper cells] could then 'awaken' once in other organs of the body and
cause secondary cancers. However, we still don't know how these cells switch
themselves into sleep mode — and what would cause them to wake up. These are
questions that need to be addressed with further research."
Dr. Sung Pil Hong
Despite these preliminary findings, the
researchers emphasize that hormone therapies are a very effective strategy
against breast cancer. To better understand the mechanics at play, possible
dangers, and how to address them, the investigators advise that further
research is needed.
Dr. Rachel Shaw, who is research information
manager at Cancer Research UK — a cancer research and awareness charity that
partly funded the recent study — also explains that the current findings
suggest a new route for cancer research.
"Although treatments for breast cancer
are usually successful, cancer returns for some women, often bringing with it a
poorer prognosis. Figuring out why breast cancer sometimes comes back is
essential to help us develop better treatments and prevent this from
happening," notes Dr. Shaw.
"This study highlights a key route
researchers can now explore to tackle 'sleeping' cancer cells that can wake up
years after treatment, which could potentially save the lives of many more
women with the disease," she explains.
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