Posted: April 4, 2013

A frequent conundrum for the oncologists is how to assess whether his or her patient with metastatic breast cancer is responding to treatment.  Scans change slowly and are expensive, cumbersome and usually involve radiation exposure.  Symptoms are unreliable, especially when the patient’s tumor burden is fairly low.  Serum tumor markers have been a useful indicator in the past but are not always elevated and sometimes fluctuate widely for no apparent reason.  Circulating tumor cells are sometimes assayed but have not proven as useful as once hoped.  Now investigators from Cambridge University in England have come up with a new approach, published in a recent New England Journal of Medicine.  Click here for the abstract; email Dr. Stark for the entire article.   The investigators found that they could identify abnormal, tumor-derived DNA floating free in the blood stream of 97% of women with metastatic breast cancer, a much higher number than for tumor markers or intact circulating tumor cells.   Free DNA changed more rapidly and dramatically than either of the other tests with changes in the patient’s status — for better or worse.    Right now the technology requires a detailed analysis of the tumor’s mutations and matching those with the protein in the blood.  If applied clinically the technology would be extremely expensive.  However, with increased volume the cost of the test should plummet.

We generally can’t cure women with metastatic breast cancer currently but with better tools to monitor their progress we will be in a much better position to custom tailor their treatment as we push ever closer to completely eradicating this disease.

Update 2020: not much has happened in this field since this original posting in 2013.  A recent article in the Journal of Clinical Oncology (click here for the abstract) discusses new approaches.  The assays have improved with newer ways to detect tumor-derived mutations.  Clearly the presence of tumor DNA is bad and its persistence is bad.  Circulating DNA is still not the standard of care in following patients with breast cancer, but arguably it should be.