Vitamin D, with its diverse molecular pathways and immunomodulatory properties, has become a crucial tool in the prevention and treatment of various cancers. It controls angiogenesis, apoptosis, differentiation, and cellular proliferation, inhibiting cancer through immune surveillance, DNA repair, and tumor suppression genes. Additionally, vitamin D signaling impacts tumor growth and metastasis in various cancer types by interacting with key oncogenic pathways like Wnt/β-catenin, NF-κB, PI3K/Akt, and p53. This review demonstrates the molecular and therapeutic implications of vitamin D in oncology, focusing on its potential as a safe, adjuvant treatment method. It emphasizes the role of vitamin D in epigenetic modification, its impact on tumor microenvironment, and its synergistic benefits when combined with immune checkpoint inhibitors and chemotherapeutic drugs. Despite promising results, genetic variations in the VDR gene continue to cause issues with bioavailability, ideal dosage, and interindividual response variability. The review also proposes future research on vitamin D's potentiality as a therapeutic adjuvant in various malignancies, including colorectal, prostate, and breast cancers, and suggests the development of non-calcemic vitamin D analogs and the incorporation of vitamin D-based methods into personalized oncology treatments.