CHICAGO (AFP) - The number of cancer cells that have broken off from the tumor and reached the blood stream affects the survival rate of patients suffering from advanced stages of prostate cancer, according to a study unveiled here. One of the problems preventing progress in the fight against cancer is identification of reliable early indicators that may signal whether a treatment can prolong the life of a patient, explained Dr. Howard Scher, a leading cancer researcher from Memorial Sloan-Kettering Cancer Center in New York and the lead author of the study. He presented this work at the 47th annual conference of the American Society of Clinical Oncology (ASCO) that is held this weekend in Chicago. More than 30,000 researchers and representatives of pharmaceutical companies are taking part in the forum. A Phase III trial known as COU-AA that involved 1,195 patients showed that the drug Zytiga developed by US laboratory Johnson and Johnson significantly improved overall survival in patients with metastatic castration-resistant prostate cancer. The drug helped reduce the number of circulating tumor cells from unfavorable to favorable counts, the researchers said. The findings could affect development of future treatment procedures because these markers could be used to evaluate the effectiveness of a new therapy in prolonging the patients life, replacing clinical trials that are longer and more expensive. In another study released Saturday at the conference, a panel of lung cancer experts known as the Lung Cancer Mutation Consortium analyzed tumor samples from 830 patients and found that half of them had undergone at least one of 10 genetic mutations known to cause cancer. Identification of these mutations should help a doctor decide which treatment is best suited for the patient.