This is an open-label, multicenter, Phase Ib dose-escalation study to assess the safety, tolerability, and pharmacokinetics (PK) of oral (PO) GDC-0941 administered in combination with PO erlotinib in patients with advanced solid tumors and patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) who have failed at least one prior chemotherapy regimen.

Inclusion Criteria:

• Documented locally advanced or metastatic solid tumors for which standard therapy either does not exist or has proven ineffective or intolerable (dose-escalation stage only)
• Documented locally advanced or metastatic NSCLC in patients who have failed at least one prior chemotherapy-based regimen for incurable disease (cohort-expansion stage only)
• Adequate organ function as assessed by laboratory tests
• Evaluable disease or disease measurable per Response Evaluation Criteria in Solid Tumors (RECIST)
• Agreement to use an effective form of contraception for the duration of the study

Exclusion Criteria:

• Any anti-cancer therapy (e.g., chemotherapy, biologic therapy, or hormonal therapy) within a specified timeframe prior to first study treatment
• Prior treatment with PI3K pathway-inhibiting agents (cohort-expansion stage only)
• History of Grade >= 3 fasting hyperglycemia or diabetes requiring regular medication
• Current clinically significant and uncontrolled systemic disease (e.g., cardiovascular, pulmonary, or metabolic)
• History of clinically significant cardiac or pulmonary dysfunction
• History of malabsorption syndrome or other condition that would interfere with enteral absorption
• Clinically significant history of liver disease
• Any condition requiring full-dose anticoagulants, such as warfarin, heparin, or thrombolytic agents
• Active autoimmune disease and/or need for corticosteroid therapy
• Known brain metastases that are untreated, symptomatic, or require therapy
• Pregnancy, lactation, or breastfeeding