A Study to Test Different Doses of BI 1831169 Alone and in Combination With an Anti-PD-1 Antibody in People With Different Types of Advanced Cancer (Solid Tumors)

This study is open to adults with different types of advanced cancer (solid tumors) that are accessible for injection and/or biopsy. This is a study for people with a life expectancy of at least 3 months after starting study treatment. The purpose of this study is to find the highest dose of a medicine called BI 1831169 that people with advanced cancer can tolerate when taken with or without a type of antibody called a checkpoint inhibitor (anti-PD-1 antibody). Another purpose is to check whether the study treatment can fight cancer. In this study, BI 1831169 is given to people for the first time. This study has 2 parts. In Part 1, participants get BI 1831169 alone for up to 3 months. In Part 2, participants get BI 1831169 in combination with a checkpoint inhibitor. Participants who take the combination treatment get BI 1831169 for up to 3 months and a checkpoint inhibitor for up to 1 year. BI 1831169 is given as an injection into the tumor, or as an infusion into the vein, or both (injection and infusion). Checkpoint inhibitors are given as an infusion into a vein. Participants get the medicines about every 3 weeks. This is called a treatment cycle. Participants visit the site study site regularly. The number of study visits vary based on the study phase and treatment response. Some visits include an overnight stay. The doctors regularly check the participants' health and monitor the tumors. The doctors also take note of any health problems that could have been caused by the study treatment.

Inclusion Criteria: * Histologically or cytologically confirmed diagnosis of advanced, unresectable and/or metastatic or relapsed/refractory solid tumors * At least one or two accessible lesions, one with a minimum lesion diameter for injection of BI 1831169 (where applicable), and one which is amenable to biopsy (where applicable). Lesions must either be easily accessible or, if not easily accessible, patient must be willing to undergo repeated procedures (e.g., image guided procedures) for both biopsies and injections of BI 1831169 * Has failed conventional treatment or for whom no therapy of proven efficacy exists, who is not eligible for established treatment options. Patient must have exhausted available treatment options known to prolong survival for their disease. This criterion does not apply to the specific indications in Part 2. Further inclusion criteria apply. Exclusion Criteria: * Previous treatment with Vesicular stomatitis virus (VSV)-based agents * Concomitant medication or condition considered a high risk for complications from injection or biopsy as per the Investigator's judgement * Presence of brain metastases * Presence of Human Immunodeficiency Virus (HIV) meeting certain criteria, active autoimmune disease or chronic active infection (Hepatitis C or B virus (HCV/HBV)) * Chronic steroid use, regardless of daily dose Further exclusion criteria apply.