Effect of SHR-1701 on chemotherapy (chemo)-induced myelosuppression: Data from a phase 3 study in HER2-negative gastric/gastroesophageal junction adenocarcinoma (G/GEJA).

335 Background: Blocking TGF-β signaling has the potential to facilitate the recovery from chemo-induced myelosuppression. SHR-1701 is a bifunctional agent targeting PD-L1 and TGF-β. Methods: In the multicenter, randomized, double-blind phase 3 study (NCT04950322), SHR-1701 plus CAPOX demonstrated a statistically significant and clinically meaningful benefit in OS compared with placebo plus CAPOX in patients (pts) with previously untreated, unresectable locally advanced or metastatic HER2-negative G/GEJA (ESMO 2024, LBA60). Here, we reported the effect of SHR-1701 on chemo-associated myelosuppression. Results: In total, 364 and 366 pts in the SHR-1701 and placebo arm received assigned treatment. As of May 20, 2024, with a KM estimated median follow-up of 13.6 mo, all study medications showed similar exposure duration between the two arms (Table). Occurrence of treatment-related adverse events was generally comparable (any grade, 97.8% in SHR-1701 arm vs 98.4% in placebo arm; grade ≥3, 62.6% vs 59.0%). SHR-1701 reduced the incidence of any grade decreased platelet count, decreased neutrophil count, and decreased white blood cell count by 8.7%, 10.1%, and 11.2%, and for grade ≥3, by 9.1%, 4.3%, and 1.6%, respectively (Table). Compared with the placebo arm, less pts in the SHR-1701 arm used platelet growth factors (30.2% vs 42.9%) and white blood cell growth factors (32.7% vs 39.6%). Conclusions: SHR-1701 showed the capacity to suppress chemo-associated myelosuppression. Clinical trial information: NCT04950322 . Safety. SHR-1701 plus CAPOX(N=364) Placebo plus CAPOX(N=366) Treatment difference (SHR-1701 vs placebo) Treatment exposure (day), median (IQR) SHR-1701/placebo 137.0 (65.5-251.5) 127.5 (62.0-190.0) NA Capecitabine 122.0 (83.0-138.0) 122.0 (73.5-135.0) NA Oxaliplatin 107.0 (66.0-123.0) 108.5 (64.0-121.0) NA Treatment-related hematological toxicities, n (%) or % Any grade Grade ≥ 3 Any grade Grade ≥ 3 Any grade Grade ≥ 3 Platelet count decreased 217 (59.6%) 69 (19.0%) 250 (68.3%) 103 (28.1%) -8.7% -9.1% Neutrophil count decreased 163 (44.8%) 44 (12.1%) 201 (54.9%) 60 (16.4%) -10.1% -4.3% White blood cell count decreased 147 (40.4%) 13 (3.6%) 189 (51.6%) 19 (5.2%) -11.2% -1.6%