(AP) — Doctors, on Wednesday, reported unusually good results from tests of two experimental drugs in women with an aggressive form of breast cancer that had spread widely and resisted many previous treatments.
One drug showed particular ability to reach tumours in the brain, which are notoriously tough to treat. The other pairs a sort of homing device for cancer cells with a payload of chemotherapy that’s released when it reaches its target.
“It’s a guided missile. It’s able to bring the chemotherapy directly to the cancer cell,” said the study leader Dr Ian Krop of the Dana-Farber Cancer Institute in Boston.
Results were disclosed at the San Antonio Breast Cancer Symposium and in the New England Journal of Medicine. From 15 per cent to 20 per cent of breast cancers are HER2-positive — they have too much of a protein called HER2 on their cell surfaces, driven by an overactive gene that promotes cancer growth.
Krop led a study of 253 such women to test the guided missile drug called T-DXd, given as an infusion every three weeks. These women had tried on average six previous treatments before the experimental drug. Different doses were tested, and 184 women got what turned out to be the best one.
Among those women, 61 per cent saw their tumours shrink at least 30 per cent. In six per cent of them, no signs of cancer were seen in at least two follow-up scans. Although the experimental drug was not tested against others, the response rate is three to four times better than what’s usually seen in this situation, Krop said.
The median time until cancer worsened was 16 months, and to see anything hold such serious cancers at bay for more than a year is exciting, he said. Side effects were substantial, though.
About 60 per cent of women had low blood counts, nausea, anaemia, or fatigue, and 15 per cent stopped treatment because of them. Most serious: Twenty-five developed lung inflammation, and four died of it.
This is a rare side effect with other drugs for this type of cancer, but it was much more common with the experimental drug. Doctors can watch patients closely and give anti-inflammatory medicines if it occurs, Krop said.
Because these cancers generally prove fatal, the drug “is still beneficial for most patients”, he said.
An independent expert, Dr Jennifer Litton of the MD Anderson Cancer Center in Houston, said it may be possible to give patients preventative anti-inflammatory medicines.
It’s worth the risk because the drug’s benefit is so great, she said. The study was sponsored by the drug’s developers, Daiichi Sankyo Inc and AstraZeneca, and they are seeking approval for the medicine in the US, Japan and Europe.
Dana-Farber’s Dr Eric Winer helped lead a study of the other experimental medicine — tucatinib, from Seattle Genetics.
“It’s a drug that’s particularly able to get into the brain,” he said, and half of the 612 participants had cancer that had spread there.
“These patients had nothing” that worked, and they’re often excluded from tests of new drugs because their outlook is so poor, Litton said.
All were given usual treatments — Herceptin and the chemo drug Xeloda — plus tucatinib or dummy pills. After two years, 45 per cent of those on tucatinib were alive versus 27 per cent of the others.
Among the women whose cancer had spread to the brain, one quarter were alive with no worsening of those tumours a year later. None of the women in the comparison group achieved that.
Diarrhoea, fatigue, nausea, and some liver side effects were a little more common with tucatinib. About six per cent of the tucatinib group stopped treatment because of side effects versus three per cent of the others.
Litton said she put some patients on studies of the drug “and they did really well”. Seattle Genetics sponsored the study and Winer and others consult for the company.