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Protein S-palmitoylation, the reversible thioesterification of cysteine side chains, is emerging as a druggable post-translational modification that couples membrane topology to oncogenic, metabolic, immune, and epigenetic networks in cancer. ZDHHC palmitoyltransferases and depalmitoylating enzymes, including acyl-protein thioesterases and palmitoyl-protein thioesterase 1, constitute a dynamic circuitry that governs the localization, stability, and signaling competence of key regulators of tumor growth, metabolic adaptation, and immune phenotype. Here, we synthesize recent structural and chemical biology advances that clarify how human ZDHHC enzymes achieve acyl-chain recognition and substrate engagement. Structural studies show that these enzymes adopt a four-transmembrane, "tent-like" fold, in which the helices create a membrane-embedded cavity for acyl-chain accommodation. We also discuss how ankyrin-repeat domains and accessory partners shape substrate recruitment and subcellular localization, and we highlight emerging high-throughput platforms that enable quantitative profiling of isoform- and site-selective modulators. We then discuss how ZDHHC-substrate circuits rewire canonical growth-factor signaling and epithelial-mesenchymal transition programs, metabolic and ferroptotic control nodes, innate immune sensing, and chromatin-linked regulation. These convergent mechanisms position ZDHHC-mediated S-palmitoylation as a context-dependent regulator of tumor progression, therapy response, ferroptosis sensitivity, and immune phenotype. Finally, we outline a translational framework encompassing clinical-stage PPT1 inhibitors, selective ABHD17 blockade, emerging ZDHHC modulators, substrate-competitive strategies targeting checkpoint palmitoylation, and selected comparator approaches affecting Wnt and Hedgehog ligand lipidation. Current evidence positions ZDHHC-mediated S-palmitoylation as a regulatory layer with potential biomarker and therapeutic relevance; however, not all reported ZDHHC-substrate associations carry equivalent evidentiary weight. Mechanisms supported by convergent site-directed, genetic, biochemical, functional, and in vivo evidence should be distinguished from associations inferred mainly from expression profiling, overexpression systems, single-model observations, or broad pharmacological perturbation. Clinical translation remains preliminary and is constrained by isoform selectivity, substrate redundancy, incomplete pharmacodynamic read-outs, and the absence of validated biomarker-guided patient stratification.