A Study Evaluating Safety, Pharmacokinetics, and Therapeutic Activity of RO6874281 as a Single Agent (Part A) or in Combination With Trastuzumab or Cetuximab (Part B or C)

Inclusion Criteria: * Radiologically measurable and clinically evaluable disease * Absence of rapid disease progression or threat to vital organs or critical anatomical sites requiring urgent alternative medical intervention * Confirmed at least one tumor lesion with location accessible to safely biopsy per clinical judgment (special requirements apply for Part C; Participants with only one target lesion and no non-target lesions can enroll after documented agreement with the Medical Monitor). * Life expectancy of greater than or equal to (\>=12) weeks * Eastern Cooperative Oncology Group (ECOG) Performance Status 0-1 * Participants with unilateral pleural effusion (other than non-small cell lung cancer \[NSCLC\] indication) should fulfill the following criteria for pulmonary and cardiac functions: Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification 0 - 1 level and New York Heart Association (NYHA) classification class 1 or better * Forced expiratory volume 1 (FEV1) \>70% and forced vital capacity (FVC) \>70% of predicted value; participants with lung metastases should present with DLCO \>60% of predicted value * Adequate cardiovascular, hematological, liver and renal function * All acute toxic effects of any prior radiotherapy, chemotherapy, or surgical procedure must have resolved to grade less than or equal to (\<=) 1, except alopecia (any grade) and Grade 2 peripheral neuropathy * Negative serum pregnancy test within 7 days prior to study treatme…