A Study of Dacomitinib in Patients With Metastatic EGFR Mutant Lung Cancer Previously Treated With Osimertinib

Inclusion Criteria:

- Written informed consent

- Advanced biopsy-proven metastatic non-small cell lung cancer

- Somatic activating mutation in EGFR in a tumor biopsy

- Prior treatment with osimertinib with response followed by disease progression

- No prior first or second generation EGFR inhibitor treatment (gefitinib, afatinib,
erlotinib)

- Archival tissue available from a tumor biopsy done after disease progression on
osimertinib or willing to undergo a tumor biopsy after disease progression on
osimertinib prior to study initiation

- Measurable (RECIST 1.1) indicator lesion not previously irradiated

- Karnofsky performance status (KPS) >/= 70%

- Age >/= 18 years old

- Ability to swallow oral medication

- Adequate organ function

- AST, ALT
- Total bilirubin
- Creatinine /= 60ml/min

- Absolute neutrophil count (ANC) >/= 1000 cells/mm3

- Hemoglobin>/=8.0 g/dL

- Platelets >/=100,000/mm3

Exclusion Criteria:

- Pregnant or lactating women

- Any radiotherapy within 1 week of starting treatment on protocol.

- Any major surgery within 1 weeks of starting treatment on protocol.

- Any evidence of active clinically significant interstitial lung disease

- Continue to have unresolved > grade 1 toxicity from any previous treatment Treatment

- Patients with a known mechanism of resistance to osimertinib that will clearly not
respond to dacomitinib therapy (i.e. known MET amplification, ALK fusion, RET fusion).

- Symptomatic brain metastases or leptomeningeal disease requiring escalating doses of
steroids