Automated bone scan index as a prognostic tool in prostate cancer patients with bone metastasis

Objectives: Bone scan index (BSI), a method of expressing the tumor burden in bone as a percent of the total skeletal mass, was developed as a quantitative tool to improve the interpretability and clinical relevance of bone scintigraphy. Baseline BSI has already been shown to be an independent prognostic factor for overall survival. The objective of this study was to evaluate whether BSI from scans throughout management are also predictive for survival and to compare BSI to prostate-specific antigen (PSA) as an outcome measure in prostate cancer patients with bone metastasis.

Methods: We retrospectively reviewed 283 bone scans from 29 prostate cancer patients. BSI and the lesion number were calculated using EXINI bone^BSI, and correlated with PSA and survival. Predictive modeling with these biomarkers was performed by Cox regression, with survival defined from time of each bone scan to death, or censored to the date of last follow-up. BSI values were dichotomized at the median, and survival distribution was estimated by the Kaplan-Meier method.

Results: BSI correlated inversely with survival in the subset of pretreatment baseline scans (ρ=-.404, p=0.030) and the overall series including subsequent in-treatment and posttreatment scans (ρ=-.362, p<0.001). BSI moderately correlated with PSA (ρ=0.592, p<0.001), while lesion number did not (p=0.374). The only statistically significant predictive variable on forward conditional Cox regression was BSI, with a relative risk of 1.089 (p<0.001). Kaplan-Meier curves for BSI dichotomized at the median 0.38 showed a significant difference between the two groups (p<0.001), with higher BSI showing shorter survival (mean survival 67.84 months vs 49.65 months for BSI<0.38 and 蠅0.38, respectively).

Conclusion: As with BSI from pretreatment scans, scans throughout management can be used to predict survival in prostate cancer patients with bone metastasis, and may have higher prognostic value than PSA. Research Support: $$graphic_3E23EEE4-DCE1-487E-BB77-A77C6B601BD3$$