Adults with cancer are at a substantially increased risk of infectious complications due to malignancy-related immune dysregulation and the immunosuppressive effects of anticancer therapies. Vaccine-preventable infections remain a significant cause of morbidity and mortality despite advances in oncologic care. This review summarizes current evidence and international guideline recommendations on vaccination strategies in adult patients with solid tumors. Inactivated and recombinant vaccines are generally safe and should be administered according to standard schedules, preferably before the initiation of immunosuppressive therapy. Although immune responses may be attenuated during treatment, available data support a meaningful clinical benefit in reducing severe infections and hospitalizations. Live attenuated vaccines are contraindicated during significant immunosuppression and should be considered only after documented immune reconstitution. Optimizing vaccination outcomes requires individualized scheduling, attention to treatment-related immune effects, and immunization of household contacts. Proactive, guideline-based vaccination should be integrated into routine oncology care to reduce infection-related complications and support treatment continuity.