Background: ALCHEMIST (Adjuvant Lung Cancer Enrichment Marker Identification and Sequencing Trial) is a clinical trial platform of the National Cancer Institute that offers biomarker analysis for high-risk resected non-small cell lung cancer (NSCLC) to support randomized trials of novel adjuvant therapies within the National Clinical Trials Network (NCTN). EA5142, a trial of adjuvant nivolumab for patients (pts) without EGFR / ALK alterations, has completed enrollment. Given the survival benefit seen with 1st-line chemo-immunotherapy (chemo-IO) for advanced NSCLC without EGFR / ALK alterations, there was compelling rationale for the launch of a trial offering concurrent immunotherapy with adjuvant chemo. Here we report updated enrollment to ALCHEMIST as of Jan 14, 2020. Methods: ALCHEMIST includes a screening trial (A151216, 5362 registered) that enrolls pts with completely resected clinical stage IB (≥4 cm)–IIIA (per AJCC 7) NSCLC. Tissue and blood are collected, biomarker testing includes EGFR sequencing, ALK FISH and PD-L1 IHC. 733 active sites are enrolling across the NCTN. Pts with EGFR mutations may enroll to adjuvant erlotinib vs observation (A081105, 352 randomized); those with ALK fusions may enroll to adjuvant crizotinib vs observation (E4512, 99 randomized). A trial offering adjuvant nivolumab vs observation regardless of PD-L1 status (EA5142, 935 randomized) recently completed enrollment. To support ongoing investigation of adjuvant immunotherapy, ALCHEMIST is adding A081801 (opens spring 2020). Pts will be randomized to one of 3 arms: chemo-IO with pembrolizumab during and after chemo vs sequential chemo followed by pembrolizumab vs chemo alone. Pts with pathological N2 nodes are eligible and can undergo postoperative radiotherapy after completing chemo. Pts are eligible if enrolled to A151216, negative for EGFR and ALK alterations, and with PD-L1 testing completed (required for stratification). Local testing for EGFR, ALK and PD-L1 will be accepted for enrollment; central testing will not delay randomization. Pts may not have received any therapy except surgery for the lung cancer and must be age >18, Eastern Cooperative Oncology Group performance status 0-1, have no active autoimmune disease requiring systemic treatment within 2 years, must not be pregnant or nursing, have no active second malignancy within 3 years and meet standard organ function values. By building off the ongoing ALCHEMIST platform, we hope to facilitate rapid enrollment to A081801 across participating NCTN sites. Clinical trial information: NCT02194738