Molecular classification and biomarkers of outcome with immunotherapy in extensive-stage small-cell lung cancer: analyses of the CASPIAN phase 3 study

Abstract

Background: We explored potential predictive biomarkers of immunotherapy response in patients with extensive-stage small-cell lung cancer (ES-SCLC) treated with durvalumab (D) + tremelimumab (T) + etoposide-platinum (EP), D + EP, or EP in the randomized phase 3 CASPIAN trial.

Methods: 805 treatment-naïve patients with ES-SCLC were randomized (1:1:1) to receive D + T + EP, D + EP, or EP. The primary endpoint was overall survival (OS). Patients were required to provide an archived tumor tissue block (or ≥ 15 newly cut unstained slides) at screening, if these samples existed. After assessment for programmed cell death ligand-1 expression and tissue tumor mutational burden, residual tissue was used for additional molecular profiling including by RNA sequencing and immunohistochemistry.

Results: In 182 patients with transcriptional molecular subtyping, OS with D ± T + EP was numerically highest in the SCLC-inflamed subtype (n = 10, median 24.0 months). Patients derived benefit from immunotherapy across subtypes; thus, additional biomarkers were investigated. OS benefit with D ± T + EP versus EP was greater with high versus low CD8A expression/CD8 cell density by immunohistochemistry, but with no additional benefit with D + T + EP versus D + EP. OS benefit with D + T + EP versus D + EP was associated with high expression of CD4 (median 25.9 vs. 11.4 months) and antigen-presenting and processing machinery (25.9 vs. 14.6 months) and MHC I and II (23.6 vs. 17.3 months) gene signatures, and with higher MHC I expression by immunohistochemistry.

Conclusions: These findings demonstrate the tumor microenvironment is important in mediating better outcomes with D ± T + EP in ES-SCLC, with canonical immune markers associated with hypothesized immunotherapy mechanisms of action defining patient subsets that respond to D ± T.

Trial registration: ClinicalTrials.gov, NCT03043872.

Keywords: Antigen presentation machinery; Biomarkers; CTLA-4; Gene expression profiling; Molecular subtyping; PD-L1; SCLC subtypes; Small-cell lung cancer; T-cell inflamed signature.

Fig. 1

CASPIAN biomarker study design and molecular datasets. CASPIAN was a randomized phase 3 trial comparing D + T + EP, D + EP, and EP as first-line therapy in patients with ES-SCLC. Tissue-based analyses were conducted using archival tumor samples obtained from 65% of patients at screening

Fig. 2

Common mutations in the CASPIAN population do not inform outcomes with immunotherapy. (A) Genes mutated in > 5% of patients in the CASPIAN FMI BEP (n = 290). (B) Association of mutation status of the most commonly mutated genes with OS (hazard ratio and 95% confidence interval, mutant versus wild-type) with immunotherapy (IO; D ± T) plus EP or EP alone. (C) Kaplan–Meier analyses of OS with IO + EP or EP in CASPIAN according to tTMB by 10 mut/Mb cut-off (D + T + EP group: median OS 9.1 [95% CI 6.9–11.4] and 10.0 [7.2–14.8] in the TMB low and TMB high cohorts, respectively; D + EP group, median OS 12.4 [95% CI 8.0–15.8] and 11.8 [8.6–14.9], respectively [16])

Fig. 3

Immune phenotype and molecular subtyping, and association with OS. (A) Proportion of patients with PD-L1 expression of ≥ 1% or < 1% on TC or IC. (B) Patients grouped by PD-L1 expression of ≥ 1% or < 1% on TC and/or IC and categorized according to SCLC molecular subtype per the method of Gay et al. [5]. (C) T-cell inflamed signature in patients with PD-L1 TC/IC ≥ 1% versus < 1% and according to SCLC molecular subtype per the method of Gay et al. [5]. (D) OS by subtype, and median OS by subtype and treatment received (immunotherapy [IO; D ± T] plus EP or EP alone), as well as in the RNAseq BEP and ITT population, with HRs and 95% CIs showing relative OS benefit of IO + EP versus EP (for total group sizes > 20 patients). Median OS and progression-free survival values for each SCLC molecular subtype in each treatment group are shown in Table S5

Fig. 4

CD8 expression and association with OS in patients receiving D ± T + EP in CASPIAN. (A) Correlation of T-cell inflamed signature score with CD8A expression (Pearson correlation methodology). (B) Inverse correlation of CD8A expression and expression of DLL3 and other neuroendocrine markers (Pearson correlation methodology). (C, D) Kaplan‒Meier analyses of (C) OS and (D) PFS with D + T + EP and D + EP versus EP in patients with high (top 30% cut-off) CD8 cell density on IHC, and OS/PFS comparisons in patients with high versus low CD8 cell density in the CD8 IHC BEP (n = 169). BEP, biomarker-evaluable population; CI, confidence interval; D, durvalumab; EP, etoposide-platinum; HR, hazard ratio; IHC, immunohistochemistry; OS, overall survival; PFS, progression-free survival; T, tremelimumab

Fig. 5

APM gene signature and its surrogate, MHC I and II, associate with OS with D + T + EP. (A) Gene expression signatures in the MSigDB enriched in patients benefitting from D + T + EP, including the APM signature (KEGG gene set). (B, C) OS by treatment arm and expression of (B) APM signature (high [top 25% cut-off] vs. low) and (C) MHC I and II signature (high vs. low) in the RNAseq BEP (n = 182). The MHC I and II signature included B2M, HLA-A, HLA-B, HLA-C, HLA-DPA1, HLA-DPB1, HLA-DMA, HLA-DMB, HLA-DQA1, HLA-DQB1, HLA-DOA, HLA-DOB, HLA-DRA, HLA-DRB1, HLA-DRB5, HLA-DQA2, HLA-DQB2, HLA-E, HLA-F, and HLA-G. (D, E) Expression of (D) APM signature and I MHC I and II signature according to SCLC molecular subtype per the method of Gay et al. [5]. (F) Inverse correlation of APM gene expression signature with expression of EZH2 and LSD1/KDM1A (Pearson correlation methodology)

Fig. 6

Distribution of MHC I expression by IHC and association of MHC I expression with OS. (A) Distribution of MHC I H-score by IHC. (B) TC positivity and intensity according to H score. (C) OS HRs and 95% CI with D + T + EP versus D + EP according to MHC I expression (%TC) by IHC, MHC I IHC BEP (n = 175)