This is a prospective, single-center, single-arm Phase I study evaluating GPRC5D-targeted PET/CT imaging in patients with plasma cell disorders, including multiple myeloma.

Participants will undergo GPRC5D-targeted PET/CT, 18F-FDG PET/CT, and 68Ga-BCMA PET/CT within 5 days whenever feasible for head-to-head comparison of lesion detection and disease assessment.

The study aims to evaluate the safety, feasibility, biodistribution, and diagnostic performance of GPRC5D-targeted PET/CT and to compare its imaging characteristics with currently available molecular imaging modalities in plasma cell disorders.

This is a prospective, single-center, single-arm Phase I interventional imaging study designed to evaluate the safety, feasibility, biodistribution, and diagnostic performance of GPRC5D-targeted PET/CT imaging in patients with plasma cell disorders, including multiple myeloma.

GPRC5D is a novel therapeutic and molecular imaging target that is highly expressed on malignant plasma cells while showing limited expression in normal tissues. Recent advances in GPRC5D-targeted immunotherapies have demonstrated promising clinical activity in multiple myeloma, highlighting the potential value of GPRC5D-directed molecular imaging for disease detection, tumor burden evaluation, treatment selection, therapeutic response assessment and prognostic evaluation.

Current standard molecular imaging with 18F-FDG PET/CT has several limitations in multiple myeloma, including reduced sensitivity in lesions with low hexokinase-2 expression and limited specificity due to inflammatory uptake.Therefore, development of novel imaging approaches targeting alternative plasma cell antigens may improve disease evaluation and provide complementary biological information.

In this study, eligible participants will undergo GPRC5D-targeted PET/CT imaging together with standard molecular imaging examinations, including 18F-FDG PET/CT and 68Ga-BCMA PET/CT. Whenever feasible, all imaging studies will be completed within 5 days to minimize interval changes in disease status and enable direct head-to-head comparison among imaging modalities.

Imaging findings from GPRC5D-targeted PET/CT will be compared with 18F-FDG PET/CT and 68Ga-BCMA PET/CT with respect to lesion detectability, disease distribution, tumor uptake characteristics, and overall disease assessment. The study will also evaluate tracer biodistribution, radiation dosimetry, image quality, and safety of the GPRC5D-targeted radiotracer.

The results of this study may help establish GPRC5D-targeted PET/CT as a novel molecular imaging tool for plasma cell disorders and support future development of GPRC5D-directed theranostic strategies in multiple myeloma.

Inclusion Criteria:

• Adults with confirmed or suspected plasma cell disorders, including multiple myeloma.
• Healthy volunteers eligible for PET/CT imaging may also be enrolled.
• Availability of recent clinical laboratory results within 1 week prior to imaging, when applicable.
• Ability to undergo PET/CT imaging procedures.
• Ability to understand the study requirements and provide written informed consent.

Exclusion Criteria:

• History of other active malignant tumors, unless considered clinically insignificant by the investigator.
• Pregnant or breastfeeding women.
• Inability to understand study procedures or comply with imaging examinations.
• Any medical or psychiatric condition that, in the investigator's judgment, may interfere with study participation or image interpretation.

Image interpretation will be performed independently by experienced nuclear medicine physicians who are blinded to participants' clinical data and to the findings of the comparator imaging studies (18F-FDG PET/CT and 68Ga-BCMA PET/CT) whenever feasible. Discordant findings will be resolved by consensus review.