Comparison of chemotherapy to chemo-immunotherapy as first-line treatment in patients with advanced large cell neuroendocrine carcinomas (LCNECs) of mixed histology: A multi-institutional international retrospective study.

8602 Background: LCNECs are a rare subtype of lung cancer, with limited clinical trial data and an unclear consensus on first-line treatment. Even less is known about the optimal treatment approach for pts with mixed LCNECs, a pathologic subtype where tumors contain both LCNEC histology as well as features of adenocarcinoma, squamous cell, or small cell lung cancer. Methods: We conducted an international multi-institutional retrospective analysis (n=13 institutions) of pts with advanced or metastatic mixed LCNECs who received 1 st -line systemic therapy with either chemotherapy alone (chemo) or chemo-immunotherapy (chemoIO) between 2010-2023. Clinical outcomes included progression-free survival (PFS), overall survival (OS), objective response rate (ORR), and treatment-related adverse events (trAEs). Survival comparisons were made via the log-rank test. Results: Seventy-three pts with mixed LCNECs received either chemo (n=42, 57.5%) or chemoIO (n=31, 42.5%). The most common chemo regimens were carboplatin/etoposide (n=27) and cisplatin/etoposide (n=8), while the most common chemoIO was carboplatin/etoposide/atezolizumab (n=19). Median age at 1 st -line therapy initiation was 65 (IQR: 60-72). 64% of pts were male (n=47). The majority were former smokers (n=41, 56.2%), with 22 current smokers (30.1%), and 10 non-smokers (13.7%). Mixed histologies included LCNEC/NSCLC (n=45, 56.2%), LCNEC/SCLC (n=17), LCNEC/carcinoid (n=1), and unspecified mixed LCNEC (n=10). Median PFS for chemo was 5 months (95% CI 2.7-9.2) vs. 6 months (95% CI 4.4-8.3) for chemoIO ( p=0.86). Median OS for chemo was 14.2 months (95% CI 10.4-22.5) vs. 17.2 months (95% CI 9.4-27.2) for chemoIO ( p=0.66). The ORR did not differ between chemo (n=18, 45%) and chemoIO (n=15, 48.4%) ( p=0.81). In the chemo group, 60% (n=25) experienced trAEs of any grade, with 23.8% (n=10) experiencing grade 3+ events and four requiring hospitalizations. For chemoIO pts, 61% (n=19) experienced trAEs, with 25.8% (n=8) experiencing grade 3+ events and six requiring hospitalizations. Neutropenia was the most common grade 3+ trAE for both chemo (n=5) and chemoIO (n=4). Overall, there were no significant differences between chemo or chemoIO groups for ORR ( p=0.81), all-grade trAEs ( p=0.88), grade 3+ trAEs ( p=0.84), PFS ( p=0.86), or median OS ( p=0.66). There were no significant differences in median PFS ( p=0.46) or OS ( p=0.99) for pts with mixed LCNEC/NSCLC vs. LCNEC/SCLC. Conclusions: For mixed LCNECs, there was no significant difference in PFS or OS between first-line treatment with chemo vs. chemoIO, suggesting limited benefit from immunotherapy for these pts. Additionally, survival outcomes did not differ between mixed LCNEC/NSCLC and LCNEC/SCLC, suggesting a biology primarily driven by their neuroendocrine component.