This study is evaluating the safety of a new oral drug (called GDC-1971) when it is given in combination with targeted therapy (either osimertinib or cetuximab) in people with advanced or metastatic non-small cell lung cancer, or metastatic colorectal cancerA Phase Ib Study to Evaluate the Safety, Pharmacokinetics, and Activity of GDC-1971 in Combination With Either Osimertinib in Patients With Unresectable, Locally Advanced, or Metastatic Non-Small Cell Lung Cancer, or With Cetuximab in Patients With Metastatic Colorectal Cancer

Exclusion

• Treatment with chemotherapy, immunotherapy, biologic therapy, or an investigational agent as anti-cancer therapy within 3 weeks or 5 drug elimination half-lives, whichever is shorter, prior to initiation of study treatment
• Treatment with endocrine therapy within 2 weeks prior to initiation of study drug, except for hormonal therapy with gonadotropin-releasing hormone agonists or antagonists for endocrine-sensitive cancers
• Significant traumatic injury or major surgical procedure within 4 weeks prior to Cycle 1, Day 1
• Positive hepatitis C virus (HCV) antibody test at screening
• Positive hepatitis B surface antigen (HBsAg) test at screening
• Known HIV infection
• Clinically significant history of liver disease, including viral or other hepatitis, current alcohol abuse, or cirrhosis
• Uncontrolled hypercalcemia
• Substance abuse, as determined by the investigator, within 12 months prior to screening
• Poor peripheral venous access
• Inability or unwillingness to swallow pills
• Malabsorption syndrome or other condition that would interfere with enteral absorption Chronic diarrhea, short bowel syndrome, or significant upper GI surgery including gastric resection, a history of inflammatory bowel disease (e.g., Crohn's disease or ulcerative colitis), or any active bowel inflammation (including diverticulitis)
• Serious infection within 4 weeks prior to screening
• History of malignancy within 3 years prior to screening
• Known and untreated, or active central nervous system (CNS) metastases (progressing or requiring anticonvulsants or corticosteroids for symptomatic control)
• Leptomeningeal disease or carcinomatous meningitis
• History or presence of an abnormal electrocardiogram (ECG) that is deemed clinically significant by the investigator (e.g., complete left bundle branch block, second- or third-degree atrioventricular heart block) or evidence of prior myocardial infarction
• Left ventricular ejection fraction (LVEF) less than the institutional lower limit of normal (LLN) or <50%
• History or evidence of ophthalmic disease
• History of or active clinically significant cardiovascular dysfunction
• History of pulmonary firbrosis, organizing pneumonia, or pneumonitis

Other protocol-defined inclusion/exclusion criteria may apply.