BACKGROUND: Family caregivers play a vital role in providing care and support for patients with life-threatening hematologic diseases. Extensive patient care needs and long-term treatment trajectories can negatively affect the health of caregivers. Despite the importance of supporting caregivers, few studies examine family caregivers' experiences and support needs during treatment. OBJECTIVE: To explore the role, experiences, and needs of family caregivers of patients with hematologic malignancies during treatment. METHODS: An exploratory longitudinal qualitative study using serial semistructured interviews with caregivers of hematologic patients was carried out. Data were analyzed using thematic analysis. RESULTS: A sample of 16 caregivers completed 47 interviews. Three themes and 2 subthemes were identified: (1) committing to an unconditional mission while adjusting to a changeable situation: developing resilience over time; (2) being an invisible and inseparable sufferer: cultivating hope one day at a time; and (3) balancing between sacrificing one's own needs and self-care. CONCLUSIONS: During treatment, caregivers face long-term psychological and physical distress, social isolation, and loneliness due to the extended life-threatening situation imposing shifting challenges and needs. Future research should explore the concept of social support in caregiver resilience and investigate psychosocial interventions in hematologic caregivers. IMPLICATIONS FOR PRACTICE: Healthcare professionals should address caregiver needs throughout the patient's treatment and provide new supportive initiatives to lessen the burden of care in hematologic caregivers. Facilitating peer support and deploying a family-oriented approach considering the patient-caregiver dyad as a subject for care have implications for clinical nursing practice.