by ecancer reporter Janet Fricker

On-treatment changes in the Bone Scan Index (BSI) can be used to predict outcomes in patients with metastatic prostate cancer, reports a study in the Journal of Clinical Oncology. 

BSI is a method that was developed to measure the extent of bone metastases by expressing tumour burden in the bone as a percent of total skeletal mass.  The procedure is undertaken for every individual bone, with results for all the bones summed to arrive at a single number representing the tumour burden. 

Currently there is no imaging biomarker for metastatic prostate cancer, with bone scintigraphy proving an “imperfect modality” for quantifying disease or demonstrating treatment effects.

The study by Elizabeth Dennis and colleagues, from Memorial Sloan-Kettering Cancer Centre (MSKCC), New York, set out to test whether treatment-related changes in BSI were prognostic for survival and to compare BSI to prostate-specific antigen (PSA) as outcome measures.

Investigators retrospectively examined serial bone scans from 88 patients with castration-resistant metastatic prostate cancer (CRMPC) who had been enrolled in four clinical trials with comparable end points conducted between 1997 and 2005 at MSKCC. In each of the four studies radionuclide bone scans were collected at baseline (just before the start of treatment) and at three and six months after the base line scan. Additionally PSA levels were obtained at each of the three time points.

Results at six months show that a patient with a doubling of BSI from baseline had a 0.34 chance of surviving longer than a patient with no change in BSI. Put an alternative way, a doubling of BSI while on treatment resulted in a 1.9 fold increase in the risk of death.

Although declines in PSA were frequently seen after three and six months on treatment, these changes were not associated with survival when changes in BSI had been adjusted for.

“To summarize, this study preliminarily showed that on treatment change in BSI is strongly associated with overall survival for patients receiving chemotherapy,” write the authors. 

The study, they add, serves as a good foundation to undertake more extensive research on BSI as a quantitative measure of progression in CRMPC. 

Reference

E.R. Dennis, X Jia, I.S. Mezheritskiy, et al. Bone Scan Index: A Quantitative Treatment Response Biomarker for Castration-Resistant Metastatic Prostate Cancer. JCO. DOI: 10.1200/JCO.2011.36.5791