A cancer diagnosis is a critical event that can change the psychological, social, and emotional structure of the family in a short period of time, confronting family members with a series of emotions, new decisions, different roles, and uncertainty about the future. The psychosocial adjustment of the family after a cancer diagnosis does not mean the complete elimination of anxiety, sadness, or worry, but rather a dynamic process for the emotional, cognitive, relational, and functional readjustment of the family in the face of new conditions of the disease. In this process, the psycho-oncologist plays an important role in identifying risk factors, strengthening coping resources, facilitating family relationships, and helping to rebuild life balance. From the perspective of theoretical foundations, the biological, psychosocial, and spiritual model considers cancer as a phenomenon whose consequences are intertwined at the physical, psychological, family, social, and spiritual levels, so the patient's adaptation cannot be separated from family adjustment. Family systems theory also considers the family as a dynamic system in which a change in the status of one member can change the roles, boundaries, relationships, and communication patterns of other members. A cancer diagnosis may cause one member to assume the role of primary caregiver, change economic responsibilities, limit family social activities, or change communication patterns between parents and children. By assessing these changes, the psycho-oncologist can identify the family's vulnerabilities and adaptive capacities and design the intervention based on its actual needs. The first stage of the intervention is an assessment of the psychological and social distress of family members, as reactions after a cancer diagnosis range from normal and temporary worry to severe anxiety, depression, sleep disturbances, feelings of helplessness, and caring burnout. In addition to psychological symptoms, this assessment should also include the quality of family relationships, economic status, social support network, beliefs about the disease, and family coping resources. One of the important tasks of a psycho-oncologist in the early stages is to provide a safe space to process the shock caused by the diagnosis, as some families experience denial, confusion, fear, or intense emotional reactions in the first days and weeks. Providing emotional support and psychological education can help family members better understand their reactions and understand them as part of the process of dealing with a medical crisis. Education about the overall course of treatment and how to manage stress can also reduce feelings of instability and ambiguity, although medical information should be provided with the opinion of the treatment team and appropriate to the patient's situation. From the perspective of stress and coping theory, adjustment increases when a person is able to balance the requirements of the situation with the resources available to him, so the psycho-oncologist tries to develop the family's coping resources and teach the skills needed to cope with new situations. Problem-solving, emotion regulation, cognitive restructuring, and planning training can help the family break down complex problems into more manageable issues and reduce feelings of helplessness. One of the major barriers to coping is catastrophic thoughts about the future; for example, family members may view any physical symptom as a sign of a deterioration of the disease or see the future solely from the perspective of loss. Cognitive-behavioral interventions can help identify these thoughts and create more realistic perceptions, without denying the reality of the disease or its difficulties. A psycho-oncologist can also help the family manage uncertainty, as many stages of cancer are associated with incomplete or changeable information, and trying to achieve complete certainty may increase anxiety. Strengthening tolerance of uncertainty and teaching skills to focus on manageable things can increase psychological adjustment. Family connection is also a key foundation for adaptation, as family members may disagree about how much information should be shared with the patient, how to talk about the future, or how to make treatment decisions. By facilitating family conversations, a psycho-oncologist can help members express their feelings and needs in a clear and non-invasive manner and reach greater understanding in important decisions. In families with children, it is especially important to pay attention to the developmental and emotional needs of the children, as trying to completely hide the illness may create anxiety and misconceptions. A psycho-oncologist can teach parents how to discuss cancer, treatment, and family changes according to the child's age, and maintain a child's sense of security. Strengthening family roles is also an important element of adaptation, as the disease should not reduce the entire family identity to the "patient's family" as much as possible. Maintaining certain daily activities, social relationships, family relationships, and enjoyable activities can help maintain a sense of identity and stability. In this way, a psycho-oncologist can guide the family to set realistic priorities and strike a balance between care, treatment, and daily life. Social support also plays an important role in adaptation, and identifying sources of support can reduce the psychological and practical stress of the family. Some families avoid seeking help due to fear of judgment, social stigma, or fear of being harassed by others, and as a result, they bear more of the burden on their own, so training the skill of seeking help and activating the support network can be part of the intervention. In situations where a cancer diagnosis causes a semantic crisis, existential and meaning-based interventions can help the family have a conversation about values, hope, suffering, the future, and the meaning of family relationships. The goal of these interventions is not to create imposed meaning or unrealistic hope, but rather to help the family find a framework that can integrate the experience of illness into their life structure. In the presence of severe conflicts, family therapy can help identify dysfunctional communication patterns, reduce blame, and increase collaboration. Also, in families where a primary caregiver bears a lot of burden, the psycho-oncologist should assess the risk of burnout and strengthen the division of responsibilities and self-care. Psychosocial adjustment also includes the family's ability to maintain job and economic functioning as much as possible, so referrals to a social worker in cases of financial difficulties or access to services are considered part of holistic care. Psychological support should also be continued in subsequent periods of treatment, as initiation of treatment, physical complications, body image changes, hospitalization, or uncertain medical outcomes can alter the family's needs. After the end of active treatment, the family may also face fear of recurrence, worry about the future, and difficulty returning to normal life, so adjustment should be seen as an ongoing process and not an event limited to the time of diagnosis. One of the important uses of psycho-oncological interventions at this stage is to help reconstruct the family narrative after illness, so that cancer is part of the life experience, but does not define the entire identity of the individual and the family. The use of group interventions, family education, and telepsycho-oncology can also increase access to support, especially for families who are unable to visit regularly due to geographical distance or caring responsibilities. However, the use of digital interventions requires attention to confidentiality, data security, digital literacy, and the quality of the therapeutic relationship. Important limitations in promoting family adjustment include cultural, economic, and structural differences in families, different severity of the disease, unequal access to psychological services, lack of psycho-oncology specialists, and the focus of some health systems on the patient's physical condition. Also, adaptation is a multidimensional concept and cannot be measured only by reducing anxiety or depression, but also family functioning, communication, quality of life, social participation, and a sense of control. It is suggested that psycho-oncology services be integrated into the standard path of cancer care from the time of diagnosis, and periodic family assessment should be done alongside the patient's evaluation. Designing stage-based, family-centered, and culturally appropriate interventions, creating a clear referral pathway between the medical and mental health team, training caregivers, strengthening support groups, and purposeful use of technology can increase the effectiveness of support. It is also necessary for the treatment team members to be familiar with the principles of family communication and identifying the symptoms of psychological distress so that the family can be referred to a psycho-oncologist at the appropriate time. In general, the role of the psycho-oncologist in promoting the psychosocial adjustment of the family after a cancer diagnosis is a multidimensional and continuous process that begins with support in the initial crisis and continues with education, emotion regulation, cognitive modification, strengthening communication, activating social resources, managing the burden of care, and helping to reconstruct meaning at different stages of the disease. The ultimate goal of these interventions is to enable the family to be able to rebuild its psychosocial balance while realistically facing cancer, keep its internal and external resources active, maintain meaningful relationships, and continue family life in a flexible and sustainable way in accordance with the new circumstances.