<p>Chemotherapeutic agents effective in killing cancer cells, but not having specificity, leading to severe systemic toxicity and adverse side effects. To address this limitation, polymeric nanoparticle-based drug delivery systems have emerged as a promising approach for targeted cancer therapy. Unlike conventional chemotherapy, these nanocarrier systems utilize natural, synthetic, semi-synthetic, and biodegradable polymers to encapsulate or coat drug molecules, enabling site-specific delivery and sustained release profiles. This review comprehensively examines the recent advancements in polymeric nanocarriers, with a specific focus on their application in targeting colorectal, breast, and lung cancers. In contrast to earlier reviews that primarily discussed general nanocarrier technologies, this study emphasizes polymer selection, fabrication methods, and structure–activity relationships in achieving enhanced therapeutic efficacy and reduced off-target effects. The review highlights how modern formulations achieve superior drug entrapment efficiency, enhanced stability, improved tumor penetration, elevated plasma concentrations, and prolonged retention time. Furthermore, it discusses how different manufacturing techniques influence the formation of specific nanoforms—such as nanoparticles, nanospheres, and nanocapsules—each with unique properties suitable for specific cancer types. By comparing recent breakthroughs in polymeric nanoformulations with earlier strategies, this study outlines the shifting paradigm toward more personalized and efficient drug delivery systems. These advancements represent a significant step forward in overcoming the major limitations of traditional chemotherapy and underscore the growing potential of polymeric nanocarriers in clinical oncology.</p>