This first-in-human study of GEN-009 will be conducted in three parts in adult patients with cutaneous melanoma, non-small cell lung cancer (NSCLC), squamous cell carcinoma of the head and neck (SCCHN), urothelial carcinoma, or renal cell carcinoma (Parts B and C only). In Part A, the safety and immunogenicity of single-agent GEN 009 will be evaluated in patients with the above-noted tumor types who have completed treatment with curative intent for their disease (eg, surgical resection, neoadjuvant and/or adjuvant chemotherapy, and/or radiation therapy) and have no evidence of disease (NED) at the time of initiating vaccination with GEN-009. In Part B, up to 15 patients in each disease cohort will be enrolled and evaluated for safety, immunogenicity, and preliminary antitumor activity of GEN-009. Patients in Part B will receive GEN-009 at the schedule selected in Part A, in combination with nivolumab at the approved dose and schedule per the United States Package Insert (USPI). Part C will evaluate the safety, immunogenicity, and objective response rate (ORR) of patients with the above-noted tumor types who have received at least 1 line of standard systemic therapy that included a programmed cell death protein 1 (PD-1) or programmed death-ligand 1 (PD-L1) inhibitor for advanced, recurrent, or metastatic disease.