Tumor progression versus bone scan “flare” in new lesions detected on early bone scans in patients with chemo-naïve metastatic castration resistant prostate cancer (mCRPC) treated with placebo or enzalutamide.

Abstract

305 Background: To differentiate between bone metastasis progression vs. Tc99m scan “flare” in new lesions on early bone scans ( ≤ 12 wks), ≥ 2 additional lesions on a confirmatory scan (6 wks later) are proposed. This reduces the risk of misreading scan “flare” as progression in responding patients (pts). Independent central review (ICR) of scans from placebo (PLC)-controlled trials can help evaluate the role of confirmatory scans as PLC should neither delay progression nor elicit scan “flare”. Methods: The ICR datasets from a randomized PLC-controlled trial of enzalutamide (ENZ) in pts with chemo-naïve mCRPC were examined. Pts with ≥ 2 new lesions on Week 9 bone scans who underwent confirmatory scans were analyzed. Scan “flare” was defined as unconfirmed progression associated with responses in PSA ( ≥ 50% decline). Results: Summarized in the table. Confirmed progression on Week 9 bone scans occurred more in pts on PLC than in pts on ENZ (57% vs. 14%). In pts with unconfirmed progression, scan “flare” occurred in 80% of pts on ENZ. Of the pts with unconfirmed progression who had PSA progression, nearly 60% progressed on follow-up scans. Conclusions: The findings from this large PLC-controlled trial provide strong evidence for performing confirmatory bone scans to verify tumor progression in new lesions on early bone scans in mCRPC. For pts with unconfirmed progression, early PSA progression appears associated with progression on follow-up scans. [Table: see text]