A Study of BMS-986449 With and Without Nivolumab in Participants With Advanced Solid Tumors

Inclusion Criteria: * All participants must have a histologically or cytologically confirmed, advanced, unresectable/metastatic, solid malignancy (measurable by Response Evaluation Criteria in Solid Tumors \[RECIST\] v1.1), and have received, be refractory to, ineligible for, or intolerant of existing therapy(ies) known to provide clinical benefit for the condition of the participant. * Part 1A may have a solid malignancy of any histology. * Part 1B is restricted to participants with Non-small cell lung cancer (NSCLC). * Part 1C is restricted to participants with Triple-negative breast cancer (TNBC). * Tumor biopsy must be obtained for all participants (unless medically precluded). Exclusion Criteria: * History of Grade ≥ 3 toxicity related to prior T-cell agonist or checkpoint inhibitor therapy (eg, anti-cytotoxic T-lymphocyte-associated antigen 4 \[CTLA-4\], or anti-PD- 1/programmed death-ligand 1 \[PD-L1\] treatment, or any other antibody or drug specifically targeting T-cell co-stimulation or other immune checkpoint pathways) except those that are unlikely to re-occur with standard countermeasures. * Current or recent (within 3 months of study intervention administration) gastrointestinal disease or gastrointestinal surgery (eg, intestinal/gastric/colon resection) that could impact the absorption of study intervention. * Any significant acute or chronic medical illness which would interfere with study intervention or follow-up in the opinion of the investigator. Other protocol-defined criteria may apply.