Automated Bone Scan Index as a quantitative imaging biomarker in metastatic castration-resistant prostate cancer patients being treated with enzalutamide

Abstract

BackgroundHaving performed analytical validation studies, we are now assessing the clinical utility of the upgraded automated Bone Scan Index (BSI) in metastatic castration-resistant prostate cancer (mCRPC). In the present study, we retrospectively evaluated the discriminatory strength of the automated BSI in predicting overall survival (OS) in mCRPC patients being treated with enzalutamide.MethodsRetrospectively, we included patients who received enzalutamide as a clinically approved therapy for mCRPC and had undergone bone scan prior to starting therapy. Automated BSI, prostate-specific antigen (PSA), hemoglobin (HgB), and alkaline phosphatase (ALP) were obtained at baseline. Change in automated BSI and PSA were obtained from patients who have had bone scan at week 12 of treatment follow-up. Automated BSI was obtained using the analytically validated EXINI BoneBSI version 2. Kendall’s tau (τ) was used to assess the correlation of BSI with other blood-based biomarkers. Concordance index (C-index) was used to evaluate the discriminating strength of automated BSI in predicting OS.ResultsEighty mCRPC patients with baseline bone scans were included in the study. There was a weak correlation of automated BSI with PSA (τ = 0.30), with HgB (τ = −0.17), and with ALP (τ = 0.56). At baseline, the automated BSI was observed to be predictive of OS (C-index 0.72, standard error (SE) 0.03). Adding automated BSI to the blood-based model significantly improved the C-index from 0.67 to 0.72, p = 0.017. Treatment follow-up bone scans were available from 62 patients. Both change in BSI and percent change in PSA were predictive of OS. However, the combined predictive model of percent PSA change and change in automated BSI (C-index 0.77) was significantly higher than that of percent PSA change alone (C-index 0.73), p = 0.041.ConclusionsThe upgraded and analytically validated automated BSI was found to be a strong predictor of OS in mCRPC patients. Additionally, the change in automated BSI demonstrated an additive clinical value to the change in PSA in mCRPC patients being treated with enzalutamide.

Therapies for castration‐resistant prostate cancer in a new era: The indication of vintage hormonal therapy, chemotherapy and the new medicines

“…The computer‐aided diagnosis system shows the BSI, which provides a quantitative measure of the percentage of the adult skeleton involved in bone metastases . BSI on bone scintigraphy was a predictor of overall survival . Measurement of BSI showed that PSA is not always correlated with the level of bone metastasis .…”

“…57,66 BSI on bone scintigraphy was a predictor of overall survival. [67][68][69] Measurement of BSI showed that PSA is not always correlated with the level of bone metastasis. 29 The Prostate Cancer Clinical Trials Working Group 3 also recommends computed tomography to evaluate lymph node metastases and visceral metastases.…”

Editorial Comment to Bone scan index: A new biomarker of bone metastasis in patients with prostate cancer

“…However, as the range of each score is broad, the detailed assessments are limited. In the case of BSI, the amount (%) of bone metastasis can be calculated by adapting the artificial neural network, which enables the detection of precise baseline metastasis, as well as the range of change among metastatic lesions …”

“…Anand et al . reported the change in BSI was useful in predicting survival in castration‐resistant prostate cancer patients treated with enzalutamide …”

“…In the case of BSI, the amount (%) of bone metastasis can be calculated by adapting the artificial neural network, which enables the detection of precise baseline metastasis, as well as the range of change among metastatic lesions. 3 The BSI has been adopted in the assessment of bone metastasis among hormone-na€ ıve to hormone-resistant prostate cancer. 4,5 The cut-off of the BSI in predicting worse survival varies from 1% to 5%.…”