A new quantitative imaging bone biomarker has been identified that can assess response and is prognostic for survival in men with metastatic castration-resistant prostate cancer (mCRPC).
Called the bone scintigraphy index (BSI), it represents the first quantitative imaging biomarker in prostate cancer. In a head-to-head comparison, the BSI was superior to PSA (prostate-specific antigen)—the traditional method—in assessing response to therapy and prognosticating for survival after 3 and 6 months on therapy for mCRPC, according to a study published online ahead of print in the Journal of Clinical Oncology on January 9, 2012. Michael Morris, MD, Memorial Sloan-Kettering Cancer Center, New York City, was senior author of the paper.
Bone scintigraphy is an older technology that images bone but not the cancerous lesions themselves. It shows the effect on the bone surrounding the metastasis, and, as such, is considered an imperfect tool on its own.
BSI is a method of expressing the tumor burden in bone as a percent of the total skeletal mass based on reference man skeletal masses. The study included 88 men enrolled in 4 different clinical trials who had bone scintigraphy done at baseline, 3 months, and 6 months on therapy
The percent change in BSI from baseline to 3 and 6 months was prognostic for survival. Doubling of the BSI was associated with an almost 2-fold increase in risk of death. When compared head-to-head with PSA, change in PSA from baseline was not prognostic for survival.
“BSI tells us about response to therapy and survival. When the BSI goes up, survival is shorter, and when it goes down, survival will be longer,” Morris explained. He and his colleagues are developing a computer-generated BSI that will have wide applicability. At present, the BSI is computed manually.