A new study has found that a blood test for cancer DNA could predict if a woman is responding to the new breast cancer drug palbociclib, months earlier than current tests. Scientists from The Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust, say the test could detect in two to three weeks whether or not the drug is working, although they caution that the results need replicating before they are used clinically.
The research, published recently in the journal Nature Communications, was largely funded by the Medical Research Council (MRC). The researchers tested women with oestrogen receptor-positive breast cancer – the most common kind – who were taking part in a clinical trial of palbociclib for advanced breast cancer.
Currently, women must wait two to three months to find out, using a scan, if palbociclib is working. The new blood test instead looks for circulating tumour DNA – fragments of DNA shed by the cancer that have entered the bloodstream. The DNA mutations associated with the cancer can be detected in these samples.
The researchers found that they could predict if the palbociclib treatment would work by comparing the amount of the gene PIK3CA detected in a blood test before treatment and 15 days after starting treatment. In the study, 73 women had the PIK3CA mutation and were given blood tests before and after starting palbociclib treatment.
In these women, the researchers found that those who had a small decrease in PIK3CA circulating DNA at 15 days had a median progression-free survival of only 4.1 months, compared with women with a large decrease in PIK3CA, who had a median progression-free survival of 11.2 months. The test could allow the women in the first group for whom the treatment is not as effective to be identified early and they could consider altering their treatment.