Can Counting Cancer Cells In Your Blood Show That the Treatment is Doing its Job

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    A blood test may be enough to determine if prostate cancer treatment is working, and allow doctors to change treatment faster if it isn’t effective. A 30 percent drop in circulating tumor cells in blood samples can indicate the efficacy of prostate cancer treatment, researchers in England report in a new study published in the journal European Urology. Circulating tumor cells are cancer cells shedded by both primary and metastatic tumors, which can be detected in blood samples.

    The use of blood tests to diagnose and track cancer has garnered more attention in recent years, and CTCs have been indicated as potentially helping to determine the prognosis of breast, colon, and prostate cancers. Previous studies have also indicated the tests may be useful for judging the efficacy of treatment, for breast cancer and also for prostate cancer. The new study, based on two clinical trials of prostate cancer drugs, reveals levels of CTCs may be useful for judging whether a treatment works, the researchers say.

    “This study raises the prospect that a patient could simply have a blood test within as little as four to six weeks after starting a new treatment to indicate whether they should continue or switch to another option,” Johann de Bono, a professor of cancer research at the Institute for Cancer Research and an oncologist at The Royal Marsden, said in a press release.

    For the study, researchers reviewed data on 486 men participating in two trials: A phase 3 clinical trial testing whether prostate cancer patients already treated with chemotherapy would benefit from abiraterone and prednisone or placebo and prednisone; and another focused on men with metastatic prostate cancer who had been treated with chemotherapy.

    Overall, 64.3 percent of study participants saw a 30 percent decline in CTC count four weeks after treatment, 65.3 percent saw a 30 percent drop 8 weeks after treatment and 64.4 percent saw a 30 percent drop at 12 weeks after treatment.

    The researchers focused on a 30 percent drop after linking it to improved survival in both studies. The number was determined, based on participant evaluations, to be a more sensitive biomarker that minimized the risk of false negative evaluation of treatments.

    “For too long patients suffering from advanced prostate cancer and their clinicians have had to face a frustrating wait to find out whether a new a new cancer treatment was working,” de Bono said.

    Before the measure can be adopted for use in treatment, the researchers say larger studies are needed for confirmation, as are the results of other clinical trials regarding the benefit of earlier changes to treatment for unresponsive patients.

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