Aptamers are short, single-stranded sequences of DNA or RNA molecules, having greater binding affinity and target specificity, which make them extremely useful tools in the field of oncology for early detection and treatment of cancer. With an emphasis on their mechanisms of action, selection strategies like Systemic Evolution of Ligands by Exponential Enrichment (SELEX) and cell-SELEX, and their wide range of applications, this chapter aims to present the potential prospects of aptamer-based diagnostic methods and therapies in cancer treatments. Aptamer-based probes are essential for the detection and profiling of circulating tumor cells (CTCs) using advanced screening techniques. Additionally, aptamer-based in vivo molecular imaging techniques make it easier to detect tumors and monitor the course of the disease. The cutting-edge advancements in the field of oncology hold promising hope for developing potential therapeutics shortly. Technological advancements improve targeted drug delivery and are also utilized for certain therapies, including immunotherapy and radiotherapy (RT), which show some active responses to certain complicated cases. Newer techniques like signal-enhanced immunological aptasensors and electrochemical aptasensors make biomarker detection even more sensitive and specific. Stability, industrial scaling problems, and regulatory barriers are primarily obstructing the translation of clinical data and hindering the potential development of aptamer-based novel diagnostic tools and therapeutic agents. While exploring new molecular targets in the oncological landscape, future research should prioritize combination therapy that incorporates aptamers with traditional chemotherapy, which might show better results. Ultimately, aptamer-based approaches have enormous potential to advance personalized medicine and enhance patient outcomes when included in cancer diagnoses and treatments.