PUBLISHED ON: 20 January 2020

Each year we return to the San Antonio Breast Cancer Symposium in Texas, USA, to hear about the progress in research – from overall understanding of the disease to clinical trials bringing new treatments to patients.

San Antonio Breast Cancer Symposium 2019

Photo Courtesy © SABCS/Todd Buchanan 2019

Spotlight on secondary HER2 positive breast cancer

This year we heard the results from two clinical trials testing new drugs for secondary HER2 positive breast cancer.

The DESTINY-Breast01 trial investigated how well a drug called trastuzumab deruxtecan, or T-DXd, worked for people who had already received several treatments for secondary breast cancer, including trastuzumab emtansine (Kadcyla).

The researchers looked at how well breast cancers responded to this treatment and how long it took for the disease to progress. On average, patients taking T-DXd had 16.7 months before their disease got worse. And most of the cancers were sensitive to this drug, even though on average the trial participants had received six prior treatments for secondary disease.

T-Dxd works in a similar way to trastuzumab emtansine. It delivers substances capable of destroying cells directly to breast cancer cells, while leaving normal cells relatively untouched. The main difference between T-Dxd and trastuzumab emtansine is the substances they deliver.

However, 25 patients out of 184 taking this new drug experienced a serious side effect, a type of lung disease. If caught early, steroids can help recovery, but if left untreated it can be deadly. Signs of this side effect will need to be very closely monitored if T-Dxd reaches clinics. More studies are already ongoing to compare T-Dxd to existing treatments and establish if it could become a new standard of care for people with secondary HER2 positive breast cancer.

Tucatinib is another emerging drug for people with secondary HER2 positive breast cancer. The HER2CLIMB trial looked at how well it worked in combination with trastuzumab (Herceptin) and chemotherapy drug capecitabine (Xeloda). People taking the triple treatment had 7.8 months before their disease got worse, compared to 5.6 months for those taking trastuzumab with chemotherapy. On average they lived 4.5 months longer.

This was the first trial, as far as we are aware, to allow people whose cancer has spread to the brain to take part. The addition of tucatinib reduced the risk of disease getting worse or dying in these women by 52%. When breast cancer spreads to the brain, it is incredibly hard to treat. It’s encouraging to see that, in the future, there could be a new treatment for these patients. Researchers now want to investigate the effects of tucatinib in more detail to understand how it works in the brain.

Gearing up to skip surgery

Breast surgery is the first treatment a lot of people with breast cancer receive. But additional treatment given before surgery, called neo-adjuvant treatment, is becoming more common. Sometimes it works so well that at the time of the surgery there are no signs of breast cancer left. But some tissue is still removed with surgery to carefully check for leftover cancer cells.

The question researchers and clinicians are trying to answer now is whether some people could safely skip the surgery. To do that, we need an accurate way to check for leftover cancer without having to perform surgery.

Several different studies tested whether imaging methods, such as mammography or MRI, followed by a biopsy could accurately tell if all cancer signs are gone. However, since biopsies only take a small sample of tissue, researchers found that these methods missed around a third of patients that had some cancer left after neo-adjuvant treatment. So there’s more work to do to find accurate, less invasive ways to evaluate how well neo-adjuvant treatment worked.

Matching therapies to breast cancers

Exciting results from the UK were presented from the plasmaMATCH trial. The researchers were testing if a blood test, also called a liquid biopsy, could help to better select cancer therapies.

They showed that this blood test can quickly and accurately evaluate the genetic make-up of a patient’s secondary breast cancer and could help identify potential new treatment approaches. If genetic weaknesses that can be targeted with existing or experimental cancer treatments were detected by the test, the participants received the treatment.

We now need to further understand if this approach helps to better control breast cancer. And if so, how this test could be introduced and used at NHS hospitals across the country.

Aromatase inhibitors to prevent breast cancer

Breast cancer prevention was also covered at the conference. The biggest news was the lasting effect of an aromatase inhibitor drug called anastrozole in lowering the risk of the disease in postmenopausal women. The research has suggested that the preventive effects of this drug continue for over five years after women stop taking it.

The IBIS-II trial looked at 3,864 women at high risk of breast cancer. For five years, half of these women took anastrozole. The other half took a placebo pill, which had no effect on their chance of developing the disease. Researchers then followed the women for an additional five years. They found that those who were taking anastrozole were 50% less likely to have developed breast cancer.

Anastrozole is currently available for postmenopausal women who are at increased risk of breast cancer to help prevent the disease. However, the researchers think that the drug is not currently offered to all the women who could benefit. The treatment comes with unpleasant side effects and the decision to take preventive therapy can be difficult. But the lasting effect of the treatment could help to weigh up the pros and cons of this option.


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