Neoplasia, the pathologic process of new and uncontrolled cellular growth, represents a fundamental challenge in modern medicine, underlying the vast spectrum of diseases we call cancer. A sophisticated understanding of its principles is critical for all healthcare professionals involved in patient care. This paper provides a comprehensive framework for the diagnosis and management of neoplasia, tracing the journey from the molecular hallmarks of cancer to the implementation of multimodal, patient-centered therapeutic strategies. We begin by elucidating the core biological principles genetic instability, sustained proliferative signaling, evasion of growth suppressors, resistance to cell death, replicative immortality, induction of angiogenesis, activation of invasion and metastasis, and reprogramming of cellular metabolism. These hallmarks provide the rationale for modern diagnostic and therapeutic approaches. The diagnostic pathway is detailed, emphasizing the indispensable integration of histopathology (including immunohistochemistry and molecular diagnostics), advanced radiological imaging, and clinical staging systems. Management principles are explored through the lens of surgical oncology, radiation oncology, and medical oncology, with a focus on the evolution from cytotoxic agents to targeted therapies and immunomodulation. The critical importance of a multidisciplinary team in formulating individualized treatment plans based on tumor biology, stage, and patient factors is underscored. Finally, we discuss the expanding frontiers of precision oncology, including next-generation sequencing, liquid biopsies, and the management of treatment resistance. This paper argues that mastery of these foundational principles is essential for navigating the increasing complexity of cancer care and delivering outcomes that optimize both survival and quality of life.