Reverse PSMA Theranostic Discordance

18 F-PSMA-1007 PET/CT is widely used for selecting patients with metastatic castration-resistant prostate cancer (mCRPC) for 177Lu-PSMA radioligand therapy. We present a striking case in which multiple skeletal metastases demonstrated intense, reproducible ¹⁷⁷Lu-PSMA-617 uptake on post-therapy scintigraphy across all three treatment cycles, yet remained occult or only minimally avid on serial ¹⁸F-PSMA-1007 PET/CT. SPECT/CT confirmed anatomic lesion localization, excluding artifact. This case of “reverse theranostic discordance” challenges the assumption that diagnostic PSMA PET faithfully represents the full target landscape for radioligand therapy. Systematic SPECT/CT review after treatment cycles may reveal therapeutically relevant disease invisible to pretherapy PET.