Posted on June 4th, 2012 by
A new quantitative imaging response biomarker, the bone scan index (BSI), can assess response to treatment and predict survival in metastatic hormone-refractory prostate cancer, according to the results of a study published in the Journal of Clinical Oncology.
Men who have metastatic hormone-refractory prostate cancer have cancer that no longer responds to hormonal therapy and has spread to distant sites in the body, including the bones. These men typically undergo bone scans during treatment, but this is an imperfect tool—it images the bone rather than the cancer and there is no standard measurement of post-treatment changes. Historically there has been no reproducible or quantifiable way to measure treatment effects in bone. In other words, there has been no way to tell if a patient is responding to treatment.
The bone scan index (BSI) was developed as a quantitative tool to improve interpretability and clinical relevance of the bone scan. The BSI is a method of expressing the tumor burden in bone as a percentage of the total skeletal mass based on “reference man” skeletal masses. (Reference man provides a standard set of biologic characteristics modeled on a hypothetical young Caucasian male.)
Researchers in this study retrospectively examined serial bone scans from 88 patients with metastatic hormone-refractory prostate cancer who were enrolled in four clinical trials. They calculated BSI at baseline and at 3 and 6 months on treatment. They found that the percent change in BSI from baseline to 3 and 6 months was predictive for survival. A doubling in BSI was associated with a 1.9-fold increased risk of death.
The researchers also compared the BSI with prostate-specific antigen (PSA)—a blood test often used to determine response to treatment—and found that a change in PSA was not prognostic for survival.
The researchers found that the BSI provides a quantitative measure—as a single number—of the amount of disease progression or regression as a result of treatment. They concluded that the BSI can prognosticate for survival and is a more accurate indicator of treatment response than PSA.
The researchers are currently at work to automate the BSI so that it is computer generated rather than manual. An automated system would make the BSI available to clinicians for use as a response biomarker.
Dennis ER, Jia X, Mezheritskiy IS, et al: Bone scan index: A quantitative treatment response biomarker for castration-resistant metastatic prostate cancer. Journal of Clinical Oncology. 2012; 30(5): 519-524.
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