Suppose your doctor could tell whether your Stage I breast cancer was likely to metastasize?  What if your oncologist could monitor the response of your cancer to chemotherapy?

A new study about circulating tumor cells is bringing that day closer.  Doctors have known for decades that cancer cells can break off from a primary tumor and travel to a different part of the body.  They understood that the bloodstream is the pathway the traveling cancer cells use to find a new place to live, but they did not have a good test to find those cells called circulating tumor cells (CTC).  They also were not sure how dangerous CTC are.  A cancer cell in the blood stream is not dangerous unless it decides to settle into a vital organ and grow, and many cancer cells undoubtedly die before finding a home in a liver or lung. 

In the last few years, more labs have been developing tests to find circulating tumor cells, and scientists have been doing research to understand how the presence of those cells affects a patient’s prognosis.  In a study reported this month in The Lancet, Dr. Anthony Lucci and his colleagues at MD Anderson Cancer Center found that the presence of even one CTC at the time of surgery increased the risk for metastasis and death four times for Stage I breast cancer patients.  The more tumor cells found in the blood sample, the higher the likelihood that the woman would recur.

This research builds on earlier findings that the number of circulating tumor cells is an important prognostic factor for metastatic breast cancer patients.  This study looked at 302 women diagnosed with Stage I, II, and III breast cancer at MD Anderson.

One important finding is that the presence of the cancer cells in the blood did not correlate with other factors that doctors often use to predict recurrence, such as the number of lymph nodes that test positive for cancer.  So doctors are excited about the possibility of having a simple blood test that might give them a more accurate idea about which cancers are likely to come back.

However, more research needs to be done before this test will be routine in your local oncologist’s office.  In an interview for MedPage Today, Dr. Lucci said, "It's frustrating in a way because we now know that the cells have significance, but we just haven't moved to the point where we know what to do with that data. We don't know if these cells should warrant different therapy or additional therapy or whether or not it would be chemotherapy."

New studies with more women will begin to answer those questions.  In the future, a CTC test might help a woman decide if she really needs chemotherapy or other treatments.  If she has no cancer cells in her blood, she and her doctor might decide that surgery is the only treatment she needs for her Stage II cancer.  Conversely, a patient with a tiny Stage I cancer might find out that cancer cells are already in her bloodstream and that she needs more aggressive treatment.