A Study Investigating BG-60366 in Adults With Epidermal Growth Factor Receptor (EGFR)-Mutant Non-Small Cell Lung Cancer

Inclusion Criteria: * Histologically or cytologically confirmed diagnosis of NSCLC, carrying an EGFR activating mutation prior to receiving standard EGFR-tyrosine kinase inhibitor (EGFR-TKI) * Phase 1a general inclusion criteria: * Disease progression on prior third-generation EGFR-TKI for advanced or metastatic disease, and either progressed or ineligible for currently available standard-of-care treatment (eg, platinum-based chemotherapy) after EGFR-TKI treatment * Phase 1a safety expansion * Documentation of EGFR resistance mutations (ie, C797s) * At least ≥ 1 evaluable lesion (for Phase 1a Dose Escalation) or at least ≥ 1 measurable lesion (for Phase 1a Safety Expansion or Phase 1b Dose Expansion) per RECIST v1.1 * EGFR resistance mutations may be detected locally either from tumor tissue or circulating tumor DNA (ctDNA) in blood, and samples used for detection of resistance mutations must be collected after progression on the most recent systemic antitumor treatment * Adequate organ function * Stable Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 1 Exclusion Criteria: * Any previous histologic or cytologic evidence of small cell or combined small cell/non-small cell disease in the archival tumor tissue or tumor biopsy before enrollment * Symptomatic spinal cord compression * Brain metastases which are symptomatic and/or requiring emergency treatment (eg, starting steroid, or stereotactic radiation/whole-brain radiation within 2 weeks before first dose of study drug) * Prior treatment with fourth-generation EGFR-TKI, other CDAC/proteolysis-targeting chimeras (PROTAC) compounds targeting EGFR mutations, or other drugs with the mechanism of action specifically targeting EGFR resistance mutations (eg, C797X) (except for the first- to third-generation EGFR-TKIs) * Any history of interstitial lung disease (ILD) or ≥ Grade 2 noninfectious pneumonitis ≤ 2 years before the first dose of study drug, or has current ILD/noninfectious pneumonitis, or where suspected active ILD/noninfectious pneumonitis cannot be ruled out by imaging during screening * Uncontrollable pleural effusion, pericardial effusion, or ascites requiring frequent drainage Note: Other protocol defined Inclusion/Exclusion criteria may apply.