Determinants of Survival with Combined HER2 and PD-1 Blockade in Metastatic Esophagogastric Cancer

Abstract

Purpose: We report updated clinical outcomes from a phase II study of pembrolizumab, trastuzumab, and chemotherapy (PTC) in metastatic esophagogastric cancer in conjunction with outcomes from an independent Memorial Sloan Kettering (MSK) cohort.

Patients and methods: The significance of pretreatment 89Zr-trastuzumab PET, plasma circulating tumor DNA (ctDNA) dynamics, and tumor HER2 expression and whole exome sequencing was evaluated to identify prognostic biomarkers and mechanisms of resistance in patients treated on-protocol with PTC. Additional prognostic features were evaluated using a multivariable Cox regression model of trastuzumab-treated MSK patients (n = 226). Single-cell RNA sequencing (scRNA-seq) data from MSK and Samsung were evaluated for mechanisms of therapy resistance.

Results: 89Zr-trastuzumab PET, scRNA-seq, and serial ctDNA with CT imaging identified how pre-treatment intrapatient genomic heterogeneity contributes to inferior progression-free survival (PFS). We demonstrated that the presence of intensely avid lesions by 89Zr-trastuzumab PET declines in tumor-matched ctDNA by 3 weeks, and clearance of tumor-matched ctDNA by 9 weeks were minimally invasive biomarkers of durable PFS. Paired pre- and on-treatment scRNA-seq identified rapid clearance of HER2-expressing tumor clones with expansion of clones expressing a transcriptional resistance program, which was associated with MT1H, MT1E, MT2A, and MSMB expression. Among trastuzumab-treated patients at MSK, ERBB2 amplification was associated with improved PFS, while alterations in MYC and CDKN2A/B were associated with inferior PFS.

Conclusions: These findings highlight the clinical relevance of identifying baseline intrapatient heterogeneity and serial ctDNA monitoring of HER2-positive esophagogastric cancer patients to identify early evidence of treatment resistance, which could guide proactive therapy escalation or deescalation.

Trial registration: ClinicalTrials.gov NCT01522768.

Figure 1.

IHC, ctDNA, and ⁸⁹Zr-trastuzumab PET imaging predict durable clinical benefit from trastuzumab, pembrolizumab, and chemotherapy. A, PFS of patients stratified according to baseline testing into HER2⁺ (IHC 3+ expression) or “indeterminate/heterogeneous” (IHC 2+/FISH+ or heterogeneous expression between disease sites or between testing at MSK and another site). B, Timeline of disease evolution in a patient who remains on therapy for over 30 months after a rapid and durable response. The patient had homogeneous high pretreatment ⁸⁹Zr-trastuzumab PET avidity in all sites (right) and clearance of ctDNA after pembrolizumab and trastuzumab induction. Tumor burden (cumulative unidimensional lesion measurements) declined in conjunction with ctDNA. Lesion-level unidimensional measurements and post-induction ⁸⁹Zr-trastuzumab PET demonstrated response in all lesions. C, Timeline of a patient who had a HER2⁺ primary tumor and HER2⁻ metastatic biopsy at baseline, and no ERBB2 amplification in tissue or ctDNA at any time. ctDNA maxVAF and tumor burden increased with pembrolizumab and trastuzumab induction, followed by decline once chemotherapy was added. Several lesions were trastuzumab-non-avid by ⁸⁹Zr-trastuzumab PET (dashed lines), and a mixed response in a celiac lymph node and increasing ctDNA maxVAF at 4 months were identified prior to RECIST progression. FGFR2 amplification was detected in ctDNA at baseline, which likely contributed to resistance along with intertumoral HER2 heterogeneity. D, PFS of patients in whom ctDNA was cleared by 9 weeks versus those with persistent ctDNA. E, PFS of patients with uniform response at 9 weeks versus those with mixed responses.

Figure 2.

Intratumoral and intertumoral heterogeneity associated with resistance. A, Therapeutic timeline in a patient demonstrating pretreatment HER2 heterogeneity with a HER2⁺ primary tumor and HER2⁻ but high PD-L1 CPS retroperitoneal lymph node (Supplementary Fig. S7). ERBB2 amplification was also identified in the primary tumor and ctDNA pretreatment. This patient initially responded to induction pembrolizumab and trastuzumab induction by ctDNA and radiographic measurements, but ctDNA was never cleared. Serial ctDNA identified a reappearance of ERBB2 amplification, as well as a new MET coamplification. Imaging identified new liver lesions that were later confirmed as metastases, as well as non-radiographically evident scalp lesions. Both the liver and scalp lesions were found to have strong MET expression by IHC upon progression. B, scRNA-seq analysis of 1,116 viable cells from an otherwise mostly necrotic on-treatment biopsy. Uniform manifold approximation and projection (UMAP) plots; color scale in inset indicates single tumor cell (n = 51) ERBB2 and FGFR3 RNA expression. Serial ctDNA assessment identified a pretreatment subclonal FGFR3-TACC3 fusion that expanded over time (see Supplementary Fig. S9).