A Study of JNJ-89402638 for Metastatic Colorectal and Gastric Cancers

The purpose of this study is to determine the putative recommended phase 2 dose(s) (RP2Ds) and best way to take (optimal route of administration) JNJ-89402638 and to determine the safety of JNJ-89402638 at the RP2D(s) in participants with metastatic colorectal cancer (mCRC) and metastatic gastric cancer (mGAC) and to determine the safety and tolerability of JNJ-89402638 in combination with bevacizumab or biosimilar with or without chemotherapy in participants with mCRC.

Inclusion Criteria: * For Part 1 (dose escalation), Part 2 (Arm A \[JNJ-89402638 monotherapy\]): Have histologically or cytologically confirmed diagnosis of colorectal adenocarcinoma (CRC) progressing after 2 or more prior lines of standard therapy in the metastatic/unresectable setting; For Part 2 Arm B (JNJ-89402638 + bevacizumab or biosimilar): Have histologically or cytologically confirmed diagnosis of CRC progressing after 2 or more prior lines of standard therapy in the metastatic/unresectable setting; For Part 2 Arm C (JNJ-89402638 + FOLFOX/bevacizumab or biosimilar): Have histologically or cytologically confirmed diagnosis of microsatellite stable (MSS) or proficient mismatch repair (pMMR) CRC progressing after 1 or more prior lines of standard therapy in the metastatic/unresectable setting. Participants must have previously received a fluoropyrimidine and irinotecan doublet (such as FOLFIRI); For Part 2 Arm D (JNJ-89402638 + FOLFIRI/bevacizumab or biosimilar): Have histologically or cytologically confirmed diagnosis of MSS or pMMR CRC progressing after 1 prior line of standard therapy in the metastatic/unresectable setting. Must not have received irinotecan previously for metastatic disease; For Part 2 Arm E (JNJ-89402638 monotherapy in mGAC): Have histologically or cytologically confirmed diagnosis of gastric adenocarcinoma or gastroesophageal junction adenocarcinoma progressing after 1 or more prior lines of standard therapy in the metastatic/unresectable setting * Have evaluable or measurable disease per response evaluation criteria in solid tumors (RECIST) version 1.1 1. Part 1: Must have either measurable or evaluable disease 2. Part 2: Must have at least 1 measurable lesion * Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 * Have an estimated or measured glomerular filtration rate (GFR) greater than or equal to (\>=) 30 milliliter per minute (mL/min) based on modification of diet in renal disease (MDRD) 4-variable formula Exclusion Criteria: * Active (new or progressive) brain metastases, leptomeningeal disease, or untreated spinal cord compression * Toxicity from prior anticancer therapy that has not resolved to Grade less than or equal to (\