Balneotherapy and Spa Rehabilitation in Patients with Hematological Malignancies: Current Evidence, Clinical Safety, and a Proposed Qualification Framework—A Critical Narrative Review

Background: Hematological malignancies and their treatment frequently cause fatigue, reduced physical capacity, neuropathy, pain and impaired quality of life. Exercise-based rehabilitation is increasingly recognized as part of the care of patients with hematological malignancies, whereas the role and safety of spa-based interventions, such as balneotherapy, hydrotherapy and peloidotherapy, remain uncertain. Methods: A critical narrative review of PubMed was performed. Evidence obtained in patients with hematological malignancies (direct evidence) was distinguished from evidence obtained in other oncological and non-oncological populations (indirect evidence), and each recommendation was assigned an evidence-certainty label (A–D). Results: No clinical studies evaluating balneotherapy or spa therapy in hematological malignancies were identified. Evidence supports exercise-based and functional rehabilitation for improving physical capacity, fatigue and quality of life, including in selected patients with cytopenias. Evidence for spa-specific procedures is indirect, and the laboratory thresholds used in practice derive from exercise studies and expert opinion rather than from validation for spa-specific procedures. Conclusions: The benefits documented in this population relate to rehabilitation and exercise, which can also be delivered in a spa setting; spa-specific procedures should be regarded as optional adjuncts requiring procedure-specific qualification. As a hypothesis for prospective evaluation, we also outline a framework in which the time-based eligibility criterion used in Poland is supplemented by structured clinical assessment.