Bone Scan Index: A Quantitative Treatment Response Biomarker for Castration-Resistant Metastatic Prostate Cancer

Abstract

A B S T R A C T PurposeThere 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. Patients and MethodsWe 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. ResultsEighty-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 ϭ .0089 and HR, 2.54; P Ͻ .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 ϭ .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 ϭ .012 and HR, 2.226; P ϭ .002, respectively), but while adjusting for BSI, PSA was not prognostic. ConclusionThese 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.

Dynamic Bone Imaging with99mTc-Labeled Diphosphonates and18F-NaF: Mechanisms and Applications

“…Thus, at best they represent an indirect measurement of tumor response. Consequently, even after successful systemic treatment of bone metastases, bone scans are known to improve very slowly, if at all (63). Other notable problems are false-negative results, a flare response leading to worsening of the scan appearance despite a clinical response to therapy, poor interobserver agreement, subjective interpretation, and inability to grade changes in intensity and extent (63,64).…”

Predictors of Positive Bone Metastasis in Newly Diagnosed Prostate Cancer Patients

“…However, this might be because there were just four patients with only spine metastasis in our cohort. In order to quantify and interpret the bone scan results, the bone scan index (BSI) was developed as a quantitative tool (Imbriaco et al, 1998) BSI has been strongly associated with overall survival in previous studies (Imbriaco et al, 1998;Sabbatini et al, 1999;Dennis et al, 2012). Current efforts have been focused on developing techniques to express BSI not as a fraction of skeletal mass but as a percentage of active marrow to generate more evidence for further clinical applications (Sabbatini et al, 1999).…”

Radiotrazadores empleados en medicina nuclear para el diagnóstico y seguimiento del cáncer de próstata

“…Es un méto-do altamente sensible para detectar metástasis óseas, especialmente osteoblásticas. También puede usarse para evaluar la respuesta al tratamiento, aunque no de una manera semicuantitativa, como en el caso de la tomografía por emisión de positrones con tomografía computarizada (PET/CT) 9 . Una de las mayores ventajas del gammagrama óseo es que requiere un mínimo del 5% de tasa de recambio óseo para poder detectar una lesión, mientras que los estudios anatómicos como la radiografía requieren un mínimo del 40-50% de dicho recambio para la visualización.…”