US scientists have developed a simple test to determine the severity of prostate cancer. The breakthrough could help doctors decide whether patients require aggressive radiation therapy or a gentler form of treatment. Michael Zelefsky and colleagues at the Memorial Sloan-Kettering Cancer Center in New York studied 213 men with localised prostate cancer. All the patients had received a hormone therapy called neoadjuvant androgen deprivation (NADD) and radiation therapy. NADD blocks the hormone testosterone which is linked to the formation of prostate cancer. Reporting in the Journal of Clinical Oncology, Zelefsky said that a chemical found only in malignant prostate cells is an excellent indicator of the cancer's severity. Levels of prostate-specific antigen (PSA) correlate directly to the strength of the cancer, he said on Wednesday 30 September.