Immune checkpoint inhibitor and adoptive lymphocyte transfer-based therapies have shown great therapeutic potential for cancers with high tumor mutation burden (TMB). Here, we employed mass spectrometry (MS)-based proteogenomic large-scale profiling to identify potential immunogenic human leukocyte antigen (HLA) Class ǀ-presented peptides in both melanoma, a “hot tumor” with high TMB, and EGFR mutant lung adenocarcinoma, a “cold tumor” with low TMB. We used cell line and patient-specific databases constructed using variants identified from whole-exome sequencing, as well as a de novo search algorithm from the PEAKS search algorithm to interrogate the mass spectrometry data of the Class I immunopeptidome. We identified 12 mutant neoantigens. Several classes of tumor-associated antigen-derived peptides were also identified. We constructed a cancer germline (CG) antigen database with 285 antigens and identified 42 Class I-presented CG antigens. We identified more than 1000 post-translationally modified (PTM) peptides representing 58 different PTMs. Our results suggest that PTMs play a critical role impacting HLA-binding affinity dramatically. Finally, leveraging de novo search and an annotated lncRNA database, we developed a novel non-canonical peptide discovery pipeline to identify 44 lncRNA-derived peptides that are presented by Class I. We validated MS/MS spectra of select peptides using synthetic peptides and performed HLA Class I binding assays to demonstrate binding of select neo-peptides and lncRNA-derived peptides to Class I proteins. In summary, we provide direct evidence of HLA Class I presentation of a large number of mutant and tumor-associated peptides for potential use as vaccine or adoptive cell therapy in melanoma and EGFR mutant lung cancer.