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Changing weight loss, which millions of dieters and diabetics rely on, can cause breast cancer treatments to stop working, experts have warned.
The drugs, which include Ozempic and Wegovy, have ushered in a new era in the fight against obesity, helping dieters lose up to a fifth of their body weight.
But US doctors tracking women being treated for an aggressive form of breast cancer have discovered that the injections ‘adversely affect’ how the body responds to chemotherapy and immunotherapy.
That meant patients on the jabs — collectively known as glucagon-like peptide-1 receptor agonists, or GLP-1s — were less likely to be completely cancer-free after treatment and more at risk of tumors returning.
The British consultant, clinical oncologist Dr. John Glees said the results were ‘disturbing’ and added: ‘These weight loss drugs are relatively new so it is very worrying that patients taking them were less likely to be cancer free after treatment.’
In the study, hundreds of women with triple-negative early-stage breast cancer were followed throughout and after treatment.
A few dozen were already taking GLP-1s and continued to do so while receiving cancer treatment.
Tests two years later showed that only 28 percent of the women on GLP-1 responded fully to the cancer treatments and were cancer-free.
Changing the weight-loss regimen millions of dieters and diabetics rely on could make breast cancer treatments stop working, experts have warned
US doctors tracking women being treated for breast cancer have discovered that the injections – collectively known as glucagon-like peptide-1 receptor agonists or GLP-1s – ‘adversely affect’ how the body responds to chemotherapy and immunotherapy.
More than twice as many — 63 percent — of those not given GLP-1s were cancer-free.
Dr. Bethania Santos, an oncologist and researcher at UT Southwestern Medical Center in Dallas, who presented the study at the San Antonio Breast Cancer Symposium, said: ‘GLP-1 use may need to be carefully considered during breast cancer treatment.’
The researchers also discovered that GLP-1s had infiltrated tumor cells and immune cells in samples taken from patients.
Although what this meant was not yet fully understood, Dr. Santos that it can make tumor cells more resistant to standard treatments.
Dr. Glees also told MailOnline: ‘We know obesity increases the risk of cancer, so drugs like Ozempic that help people lose weight can also reduce that risk.
‘Jabs also seem to protect the heart and possibly the brain.
“But we need to think very carefully about this new data and do more research.
“It is important that patients do not panic, but it is also important that women tell their cancer specialist if they are taking one of these GLP-1 drugs while undergoing cancer treatment.”
Checking your breasts should be part of your monthly routine so you notice any unusual changes. Simply rub and feel from top to bottom, in semicircles and in a circular motion around your breast tissue to identify any abnormalities
Symptoms of breast cancer to look out for include lumps and swelling, dimpling of the skin, changes in colour, discharge and a rash or crusting around the nipple
Other experts today also urged users of weight loss pills not to continue taking them during cancer treatment and to wait for ‘more definitive data’ on the subject.
Professor Neil Lyengar, an oncologist at Memorial Sloan Kettering Cancer Center in New York told MailOnline: ‘The patients who were prescribed weight loss drugs in this study were already taking several other diabetes drugs.
“This suggests that these patients had advanced or difficult-to-control diabetes.
‘My interpretation of these data is not that weight loss drugs reduce the effectiveness of chemotherapy, but rather that people who have advanced diabetes that requires more drugs are at increased risk of getting breast cancer back.
“This study does not answer the question of whether weight loss agents help or harm the effectiveness of cancer treatment.”
He added: ‘Given the negative impact of obesity on cancer survival, I support the use of weight loss drugs after cancer treatment is completed.
‘However, I currently do not recommend the use of weight loss drugs during cancer treatment until we have more definitive data.
But these decisions are very complex and different for each individual.’
Ozempic, Wegovy and a similar drug Mounjaro are self-administered weekly.
Limited studies have suggested weight loss jabs may be helpful in reducing the risk of breast cancer and other cancers.
One in seven women in the UK will be diagnosed with breast cancer in their lifetime – around 56,000 a year – making it the most common cancer in the UK.
The number is around 300,000 annually in the United States. About 85 percent of women diagnosed with breast cancer survive more than five years.
However, triple negative breast cancer – which accounts for around 15 per cent of all breast cancers in the UK and US – is far more difficult.
It typically grows and spreads faster than other types of breast cancer and has fewer treatment options.
It is also more challenging to treat because it does not have receptors for hormones such as estrogen – for which there are targeted treatments.
On average, around 77 percent of women with triple-negative breast cancer will survive their cancer for five years or more after they are diagnosed, but depending on the stage, this can drop to as low as 12 percent.
Breast cancer specialist and author Dr. Liz O’Riordan told MailOnline: ‘This is an important study and more research is needed.
‘It appears that GLP-1s can make cancer cells less responsive to chemotherapy and immunotherapy.
“This will mean their cancers are much more likely to return.
“On the other hand, we think that giving GLP-1s to women after they’ve finished cancer treatment to keep their weight down may reduce the likelihood of cancer recurrence.
“We need to think more about how these patients are managed and more research to understand what’s going on.”
