Breast cancer blood test tracks treatment response

A blood test is being developed that could help doctors monitor how breast cancer tumours respond to therapy.

'These results hold the promise of a system that could allow us to modify someone's treatment as their cancer changes', says Professor Peter Johnson, the chief clinician at Cancer Research UK, which part-funded the study.

Currently, biopsies and scans are used to monitor tumours during treatment, but these can be slow and don't always provide reliable information. Results from an early study indicate that this blood test could potentially provide a faster, more reliable, and less invasive alternative. The test is among a growing number being developed for several aspects of cancer diagnosis (see BioNews 656 and 677).

Scientists tested the blood of 30 women with an advanced form of cancer called metastatic breast cancer. The blood was screened for several cancer components, called biomarkers. These included a cancer protein, tumour DNA, and whole tumour cells circulating in the blood. The levels of each were compared with the disease's progression, as assessed by computerised tomography (CT) scans.

They discovered that the amount of one biomarker, tumour DNA, correlated well with the extent of the cancer: the more the disease progressed, the more tumour DNA there was in the blood sample.

'Fragments of DNA are shed by cancer cells when they die, meaning they can be detected in blood samples using sensitive new sequencing techniques', says Professor Carlos Caldas of the Cancer Research UK Cambridge Institute, who co-led the study. 'The levels of tumour DNA tell us how the cancer is responding to treatment'.

The test works by checking the blood sample for two mutated genes, which are commonly associated with tumours. However, not all breast cancers have mutations in these genes. In fact, 52 women with metastatic breast cancer were recruited for the study, but only 30 of the women had tumours with the mutations used in the test. This limits the usefulness of the test to women whose tumour cells carry these specific mutations.

Metastatic breast cancer is currently incurable. Treatment is intended to extend the patient's lifespan, rather than eliminate the cancer. It is therefore hoped that the blood test could supplement CT scans to improve the quality of life of these patients. 'By understanding the point at which a cancer changes we can select the most effective treatments and minimise side effects for patients', says Professor Caldas.

The results, published in the New England Journal of Medicine, are from a small pilot study. There are plans for a larger, randomised trial to determine whether the test could change how the cancer is treated or improve patient survival times.

Professor Daniel Haber of Massachusetts General Hospital Cancer Center, who was not involved in the study, told Nature News: 'This is a powerful technology. It can be very scalable, inexpensive, and useful'.