Final analysis of the randomized phase 2 part of the ASPEN-06 study: A phase 2/3 study of evorpacept (ALX148), a CD47 myeloid checkpoint inhibitor, in patients with HER2-overexpressing gastric/gastroesophageal cancer (GC).

332 Background: Evorpacept (Evo) is a high affinity, CD47-blocker with an inactive Fc region designed to safely magnify anticancer antibody dependent cellular phagocytosis. Evorpacept is being evaluated across cancers, in combination with anticancer antibodies and checkpoint inhibitors. Methods: The ASPEN-06 randomized phase 2 trial evaluates Evo in combination with standard trastuzumab (T), ramucirumab (R) and paclitaxel (P) for the treatment of patients with HER2+ GC. Patients with 2 nd or 3 rd line HER2+ advanced or metastatic GC that has progressed on or after prior anti-HER2 therapy were randomized to Evo (30 mg/kg Q2W) plus TRP or TRP. HER2 status was determined in the most recent GC tissue sample. Primary study objectives were to compare confirmed ORR of Evo-TRP to an assumed ORR of RP (=30%) with one-sided alpha error of 0.025 and to identify a clinically meaningful contribution of Evo to TRP in ORR (delta>10%). Results: Among the entire randomized population (N=127) the ORR was 40.3% (Evo-TRP) and 26.6% (TRP), respectively. The difference between Evo-TRP's ORR compared to historical RP's ORR was not statistically significant (p=0.095), but Evo-TRP's ORR demonstrated a meaningful delta of 13.7% over TRP's ORR (p=0.028 in an exploratory analysis). Median DOR for Evo-TRP and TRP was 15.7 and 7.6 months, respectively. In a prespecified population with HER2+ disease in fresh tumor tissues after prior anti-HER2 treatment (N=48), Evo-TRP's ORR (54.8%) compared favorably to historical RP's ORR (p=0.030) with a delta of 31.7% over TRP's ORR of 23.1% (p=0.004 in an exploratory analysis). Evo-TRP was well tolerated with a safety profile consistent with prior experience. Updated results including PFS will be presented at the meeting. Conclusions: The addition of Evo to TRP showed promising activities in HER2+ GC. The magnitude of response was greatest in tumors identified as HER2+ using fresh biopsies emphasizing the importance of biopsies post anti HER2 therapy. Consistent with Evo’s mechanism of enhancing antibody dependent phagocytosis, these data support its ongoing investigation as an adjunct to anti-HER2 gastric cancer therapy. Clinical trial information: NCT05002127 .