[Expression of GPRC5D in newly diagnosed patients with multiple myeloma detected by flow cytometry and its prognostic value].

Objective: To investigate GPRC5D expression on myeloma cells in newly diagnosed multiple myeloma (NDMM) patients and evaluate its prognostic significance. Methods: This study retrospectively analyzed the clinical data of 65 patients with NDMM treated at the Affiliated Hospital of Xuzhou Medical University from April 2023 to April 2024. The expression of GPRC5D on the surface of myeloma cells in all patients was detected with flow cytometry before induction therapy, and patients were stratified into high and low GPRC5D expression groups based on the median GPRC5D positivity rate. Clinical characteristics, immune status, treatment response after induction therapy, and prognosis were compared between the two groups. Results: The median positive rate of GPRC5D in the plasma cells of 65 patients with NDMM was 32.68%. Based on this threshold, patients were categorized into the high (33 cases, GPRC5D positive rate ≥ 32.68%) and low (32 cases, GPRC5D positive rate <32.68%) GPRC5D expression groups. Compared with the low GPRC5D expression group, the high GPRC5D expression group demonstrated a higher proportion of 1q21 gain (78.8% vs 43.8%, P=0.004), a higher incidence of immunoparesis involving ≥2 uninvolved immunoglobulins (87.9% vs 62.5%, P=0.018), and severe immunoparesis (59.4% vs 33.3%, P=0.046). Further, CD16(+)CD56(+) cell levels were lower in the high GPRC5D expression group [ (16.60±8.70) % vs (27.78±15.78) %, P=0.005]. No significant difference was observed in the overall response rate between the high and low GPRC5D expression groups (78.8% vs 93.8%, P=0.165). However, the high GPRC5D expression group exhibited a significantly lower rate of achieving very good partial remission or better (42.4% vs 78.2%, P=0.003) and a lower MRD negativity rate (30.0% vs 68.8%, P=0.002). Compared with the low GPRC5D expression group, patients with high expression demonstrated a significantly shorter median progression-free survival (11.2 months vs not reached, P=0.002), whereas the median overall survival was not reached in either group, with no statistically significant difference (P=0.069) . Conclusions: The GPRC5D positivity rate in the plasma cells of patients with NDMM is associated with 1q21 gain and immune status. High GPRC5D expression at diagnosis may predict poor response to induction therapy and an unfavorable prognosis.