Inclusion Criteria - Histologically or cytologically documented, locally advanced or metastatic solid tumors for which standard therapy either does not exist or has proven ineffective or intolerable - Evaluable disease or disease measurable per Response Evaluation Criteria in Solid Tumors (RECIST) - Life expectancy ≥ 12 weeks - Adequate hematologic and end organ function - Agreement to use an effective form of contraception for the duration of the study Exclusion Criteria - History of prior significant toxicity from another MEK pathway inhibitor requiring discontinuation of treatment - History of prior significant toxicity from another PI3K pathway inhibitor requiring discontinuation of treatment - Allergy or hypersensitivity to components of the GDC-0973 or GDC-0941 formulations - Palliative radiotherapy within 2 weeks prior to first dose of study drug treatment in Cycle 1 - Experimental therapy within 4 weeks prior to first dose of study drug treatment in Cycle 1 - Major surgical procedure or significant traumatic injury within 4 weeks prior to first dose of study drug treatment in Cycle 1, or anticipation of the need for major surgery during the course of study treatment - Prior anti-cancer therapy within 28 days before the first dose of study drug treatment in Cycle 1 - History of diabetes requiring daily medication, or history of Grade ≥ 3 fasting hyperglycemia - Current severe, uncontrolled systemic disease - History of clinically significant cardiac or pulmonary dysfunction - History of malabsorption or other condition that would interfere with enteral absorption - Clinically significant history of liver disease (including cirrhosis), current alcohol abuse, or current known active infection with HIV, hepatitis B virus, or hepatitis C virus - Any condition requiring anticoagulants, such as warfarin, heparin, or thrombolytics - Active autoimmune disease - Uncontrolled ascites requiring weekly large volume paracentesis for 3 consecutive weeks prior to enrollment - Pregnancy, lactation, or breastfeeding - Known brain metastases that are untreated, symptomatic, or require therapy to control symptoms - No other history of or ongoing malignancy that would potentially interfere with the interpretation of the pharmacodynamic or efficacy assays