A Study to Investigate the Efficacy and Safety of Dato-DXd With or Without Osimertinib Compared With Platinum Based Doublet Chemotherapy in Participants With EGFR-Mutated Locally Advanced or Metastatic Non-Small Cell Lung Cancer

This study will assess the effect of Dato-DXd in combination with osimertinib or Dato-DXd monotherapy versus platinum-based doublet chemotherapy in terms of progression-free survival (PFS).

This is a Phase III, open-label, 3-arm, multicenter study assessing the effects of Dato-DXd in combination with osimertinib or Dato-DXd monotherapy versus platinum-based doublet chemotherapy in participants with epidermal growth factor receptor gene mutation (EGFRm) locally advanced or metastatic non-small cell lung cancer (NSCLC) whose disease has progressed on prior osimertinib treatment.

Participants will be randomized in a 1:1:1 ratio to one of the following intervention groups:

1. Dato-DXd + osimertinib combination therapy
2. Dato-DXd monotherapy
3. Platinum-based doublet chemotherapy

Participants will receive study intervention until Response Evaluation Criteria in Solid Tumors, Version 1.1 (RECIST v1.1) -defined radiological progression by the investigator, unacceptable toxicity, or other discontinuation criterion is met.

After study intervention discontinuation, all participants will undergo an end of treatment (EoT) visit within 35 days of discontinuation and will be followed up for safety assessments 28 (+ 7) days after their last dose of study intervention.

Eligibility Criteria:
Inclusion Criteria:

* Histologically or cytologically confirmed non-squamous NSCLC.
* Must have evidence of documented pre-existing EGFRm information (EGFRm known to be associated with (epidermal growth factor receptor \[EGFR\] tyrosine kinase inhibitor \[TKis\] sensitivity \[Ex19del, L858R, G719X, S768I, or L861Q\], either alone or in combination with other EGFR mutations, which may include T790M).
* Documented extra-cranial radiologic progression on prior osimertinib monotherapy (as most recent line of treatment) in the adjuvant, locally advanced, or metastatic setting.
* Less than or equal to (\<=2) prior lines of EGFR TKIs (osimertinib is the only permitted prior third generation EGFR TKI).
* At least one lesion, not previously irradiated, that qualifies as a RECIST v1.1 TL at baseline and can be accurately measured at baseline.
* World Health Organization (WHO)/Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
* Adequate bone marrow reserve and organ function within 7 days before randomization.

Exclusion Criteria:

* Use of chemotherapy, vascular endothelial growth factor inhibitor, immunotherapy or any anti-cancer therapy in the metastatic setting. Platinum-based chemotherapy in non-metastatic setting within 12 months prior to randomization.
* History of another primary malignancy except for malignancy treated with curative intent with no known active disease within 2 years before the first dose of study intervention.
* Any evidence of severe or uncontrolled systemic diseases, including, but not limited to active bleeding diseases, active infection, active ILD/pneumonitis, cardiac disease.
* Has significant third-space fluid retention (example \[eg.\], ascites or pleural effusion) as judged by the investigator and is not amenable for required repeated drainage.
* History of non-infectious ILD/pneumonitis including radiation pneumonitis that required steroids or drug-induced ILD, has current ILD/pneumonitis, or has suspected ILD/pneumonitis that cannot be ruled out by imaging at screening.
* Has severe pulmonary function compromise resulting from intercurrent pulmonary illnesses.
* Unstable spinal cord compression and/or unstable brain metastases.
* Participants with symptomatic brain metastases (including leptomeningeal involvement).
* Clinically significant corneal disease.
* Uncontrolled infection requiring IV antibiotics, antivirals, or antifungals, suspected infections or inability to rule out infections.
* Has known human immunodeficiency virus (HIV) infection that is not well controlled.