Bone scan index: a quantitative treatment response biomarker for castration-resistant metastatic prostate cancer.
OBJECTIVE
There is currently no imaging biomarker for metastatic prostate cancer. The bone scan index (BSI) is a promising candidate, being a reproducible, quantitative expression of tumor burden seen on bone scintigraphy. Prior studies have shown the prognostic value of a baseline BSI. This study tested whether treatment-related changes in BSI are prognostic for survival and compared BSI to prostate-specific antigen (PSA) as an outcome measure.


METHODS
We retrospectively examined serial bone scans from patients with castration-resistant metastatic prostate cancer (CRMPC) enrolled in four clinical trials. We calculated BSI at baseline and at 3 and 6 months on treatment and performed univariate and bivariate analyses of PSA, BSI, and survival.


RESULTS
Eighty-eight patients were scanned, 81 of whom have died. In the univariate analysis, the log percent change in BSI from baseline to 3 and 6 months on treatment prognosticated for survival (hazard ratio [HR], 2.44; P = .0089 and HR, 2.54; P < .001, respectively). A doubling in BSI resulted in a 1.9-fold increase in risk of death. Log percent change in PSA at 6 months on treatment was also associated with survival (HR, 1.298; P = .013). In the bivariate analysis, change in BSI while adjusting for PSA was prognostic at 3 and 6 months on treatment (HR, 2.368; P = .012 and HR, 2.226; P = .002, respectively), but while adjusting for BSI, PSA was not prognostic.


CONCLUSIONS
These data furnish early evidence that on-treatment changes in BSI are a response indicator and support further exploration of bone scintigraphy as an imaging biomarker in CRMPC.
Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Elizabeth R
ER
Dennis
Xiaoyu
X
Jia
Irina S
IS
Mezheritskiy
Ryan D
RD
Stephenson
Heiko
H
Schoder
Josef J
JJ
Fox
Glenn
G
Heller
Howard I
HI
Scher
Steven M
SM
Larson
Michael J
MJ
Morris
D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000097:blood*; D001859:Bone Neoplasms / Q000000981:diagnostic imaging* / Q000401:mortality / Q000556:secondary*; D018450:Disease Progression; D019008:Drug Resistance, Neoplasm; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D016017:Odds Ratio; D009919:Orchiectomy; D011237:Predictive Value of Tests; D011379:Prognosis; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000276:immunology / Q000378:metabolism / Q000401:mortality* / Q000473:pathology*; D011877:Radionuclide Imaging; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D016019:Survival Analysis
D014408:Biomarkers, Tumor; D017430:Prostate-Specific Antigen