New Test May Help Better Treat Prostate Cancer

By Margarita Nahapetyan

A new test that looks for tumor cells in the blood may give doctors a better opportunity to figure out whether chemotherapy is helping a prostate cancer patients, researchers reported this week.

A study in The Lancet Oncology medical journal showed that counting number of cancer cells that have broken away from the tumor in the bloodstream was found to be far more reliable than the blood marker currently used to track the disease, and helped to concentrate treatment more effectively.

Prostate cancer is one of the most common types of cancer that affects men more often when they are over the age of 50 years. When hormonal therapy is not being effective anymore, a patient is deemed to suffer from castration-resistant prostate cancer. The progression of such disease is very difficult to track, as well as the to predict as to how patients will respond to chemotherapy.

Professor Howard Scher from the Memorial Sloan Kettering Cancer Center, New York City, USA and the team of researchers used the IMMC38 data to determine the association between circulating tumor cells number (CTCs), before and after the treatment, and subsequent survival in 164 patients. The researchers also evaluated other factors, such as changes in the prostate specific antigen (PSA) and baseline lactate dehydrogenase (LDH). Circulating tumor cell number was determined using the Cell Search™ (Veridex) system which was approved by US Food and Drug Administration. Patients in IMMC38 had progressive, metastatic prostate cancer and were beginning their first-line chemotherapy.

Scientists used concordance probability estimates to measure the discriminatory power of variables for identifying patients with low and high risk of survival. Values of 1, 0, and - 1 were used to reflect perfect positive concordance, no concordance, and perfect negative concordance, accordingly.

What the researchers found was that, before treatment, high numbers of circulating tumor cells and PSA, used at the current test, were associated with the increased risk of death. However, 4, 8, and 12 weeks after the treatment, changes in CTC number were still strongly associated with the risk, while changes in prostate specific antigen were associated only marginally. The study confirmed that pre-treatment CTC number can be used to predict survival of patients starting first-line chemotherapy, and that changes in the levels of circulating tumor cells were more predictive of response to treatment than the level of prostate specific antigen.

In monitoring patients with metastatic, castration-resistant prostate cancer, bone scans and changes in prostate specific antigen values no potential for predicting benefit from therapy was shown. And those trials that involved patients with metastatic breast, colorectal, and prostate cancer have shown that pre-treatment tumor cell counts could stratify patients into prognostically favorable and unfavorable groups, the authors said

"CTC number ... can be used to monitor disease status and might be useful as an intermediate endpoint of survival in clinical trials", said Howard Scher. "Use as an intermediate or surrogate endpoint for survival could shorten the timeline for drug approval," although he pointed out that "several prospective trials are needed to generate evidence to guide the use of biomarkers." He added that the model that best predicted survival incorporated pre-treatment CTC number and LDH concentration alongside post-treatment changes in CTC number.

John Neate, chief executive of The Prostate Cancer Charity, a London-based advocacy group said that "Once prostate cancer has advanced to the stage where chemotherapy is an option - which is at a late stage of the disease, unlike in many other cancers - one of the problems that doctors face is uncertainty about the effectiveness of the treatment."

"Progress is not easy to track with current tests. They work reasonably well but something better is needed. Whilst further trials are necessary, this new research shows that measuring the number of circulating tumor cells seems to improve prediction of how men will respond to chemotherapy," concluded Neate in his statement.