The role of the psycho-oncologist in facilitating treatment decision-making and the family's adaptation to the cancer treatment process is one of the essential components of family-centered psychological care in the comprehensive oncology system, because the diagnosis of cancer confronts not only the patient, but also the whole family with a series of complex decisions, emotional concerns, and new roles and responsibilities. From the time of the announcement of the diagnosis to the choice of treatment method, the initiation of chemotherapy, radiation therapy, surgery, treatments, Targeted and supportive care, the family is exposed to extensive medical information that can be difficult to process and evaluate in situations of anxiety and stress. In such a situation, treatment decision-making is not simply a medical process, but a psychological and family experience influenced by beliefs, values, emotions, interpersonal relationships, supportive resources, and family members' perceptions of the future. The theoretical foundations of this field are based on the biological-psychosocial model and the family-centered approach of care, in which cancer is considered as a phenomenon affecting the whole family system. According to this viewpoint, any change in the patient's situation can affect the psychological and functional balance of the family, and the reaction of the family members, in turn, affects the quality of the patient's support. One of the important frameworks in this regard is shared decision-making, which emphasizes the conscious participation of the patient and, if he or she wishes, the family members in the dialogue with the treatment team. The psycho-oncologist plays the role of a psychological facilitator in this process, helping the patient and the family to identify emotional and cognitive barriers to decision-making, better process the information provided by the physician, and clearly articulate their preferences and values. Of course, it is the responsibility of the treating physician to provide expert information about the effectiveness, complications, and risks of treatments, and the psycho-oncologist should not replace medical decision-making. One of the most important challenges for the family at this stage is the anxiety caused by the need to choose between different treatment options. By examining these patterns, the psycho-oncologist can help reduce the stress of decision-making and increase the ability to realistically assess the situation. One of the cognitive foundations of this intervention is to pay attention to mental biases and catastrophic thinking that may be exacerbated in a crisis situation. For example, the family may perceive any delay in treatment as a loss of the opportunity to recover or perceive the possible complications of a treatment as a definitive outcome. In such a setting, cognitive intervention helps family members to distinguish between possibility, certainty, and personal perception. Also, training the skills of asking clear questions of the doctor, taking notes of therapeutic information, reviewing available options, and participating in counseling sessions can increase the quality of decision-making. On the other hand, the family's adjustment to the cancer treatment process requires a readjustment of family roles and responsibilities. Initiation of treatment may result in a change in the division of duties, economic status, childcare, work activities, and emotional relationships. By assessing the family structure and identifying sources of support, a psycho-oncologist can help members divide responsibilities according to each individual's ability and circumstances. In this way, it is important to strengthen family resilience, as families who are able to adapt to changes are better able to cope with the patient's treatment requirements and physical and psychological fluctuations. Another important application of the intervention is to manage family conflicts around treatment decisions. The patient's spouse may emphasize the continuation of aggressive treatments, while children or other relatives may have a different view. Sometimes the patient wants to be more involved in decision-making, but family members try to make all the choices for him or her because of concern and a desire to protect him. In such a situation, the psycho-oncologist maintains the patient's autonomy and right to choose, provides a respectful atmosphere for dialogue and teaches family members to discuss differences of views without blame and psychological pressure. Paying attention to the patient's preferences, decision-making capacity, and the extent of family involvement are among the basic principles of this process. In families where the patient wishes to share therapeutic information directly with his close members, joint psychological sessions can be held to address the concerns, expectations, and emotional needs of the members. Emotion regulation training is also an important part of these interventions, as anxiety, anger, sadness, fear of death, and feelings of helplessness may reduce the family's ability to have rational dialogue and collaborative decision-making. The psycho-oncologist can strengthen the family's psychological capacity to cope with different stages of treatment by using cognitive-behavioral techniques, problem-solving training, communication skills, and relaxation strategies. In the acceptance and commitment approach, members of the familylearn that in situations of medical uncertainty, it is not always possible to achieve a definitive answer and can make decisions that are tailored to their values and priorities despite their concerns. This approach helps to reduce the exhausting effort to control all aspects of the disease and directs the family's attention to actions that can be taken in the present. Another important area is the psychological preparation of the family for possible complications of treatment. Being aware of the patient's physical changes, fatigue, nausea, pain, changes in appearance, and functional limitations can reduce the severity of the family's trauma in the face of these conditions, provided that the training is accurate and appropriate to the information of the treatment team. The psycho-oncologist can also help family caregivers distinguish between effective support and extreme care, and maintain the patient's independence as much as possible. Strengthening family self-efficacy is another important goal of the intervention, which means that members feel that they are capable and skilled enough to manage daily issues, communicate with the treatment team, and provide emotional support to the patient. In this context, identifying social support resources, using social support services, support groups, and caregiver training programs can reduce the stress of treatment. Also, in families where children and adolescents are present, it is essential to provide age-appropriate education and level of understanding so that the changes caused by the illness are not experienced in a frightening and ambiguous way. A psycho-oncologist can help parents talk about the illness and the stages of treatment in an honest, understandable language appropriate to their children's cognitive capacity. In families where long-term treatment or relapse occurs, the need to re-evaluate psychological adjustment increases, as strategies that were effective in the early stages may not meet the needs of the family in the later stages. Therefore, continuous follow-up and periodic evaluation of psychological distress should be part of the care plan. One of the main challenges in this area is the difference between the patient's demands and the expectations of the family, which can lead to conflict and decreased emotional support in the absence of appropriate dialogue. Another challenge is the time constraints of medical sessions and the high volume of therapeutic information, which reduces the opportunity for psychological processing of decisions. Cultural beliefs, differences in the level of health literacy, economic problems, unequal access to health services, and the family's previous experiences of cancer also affect decision-making and adjustment. Limitations of psycho-oncological interventions include the dependence of the results on the severity of the disease, the quality of the treatment team's communication, the level of involvement of family members, and access to specialized services. It is also not expected that psychological interventions will eliminate all conflicts or concerns in the family, as part of the psychological stress stems from the true nature of the disease and the difficult conditions of treatment. To increase effectiveness, it is suggested that the psychological evaluation of the family begin from the early stages of diagnosis and continue at critical points such as the choice of treatment method, the initiation of chemotherapy, the end of active treatment, and the entry into the follow-up phase. Designing family-centered protocols, holding joint meetings in coordination with the oncology team, teaching informed decision-making skills, and developing face-to-face and remote counseling services can increase families' access to specialized support. Also, the use of valid tools to measure distress, anxiety, family conflict, and self-efficacy of caregivers can help to accurately identify needs and assess the consequences of intervention. Finally, the role of the psycho-oncologist in facilitating therapeutic decision-making and family adjustment goes beyond reducing anxiety and providing emotional support, and includes empowering the family to participate consciously, maintain effective communication, manage conflicts, accept changes, and rebuild the balance of life in the context of the disease. Such an approach can transform the cancer treatment process from a purely experience based on fear and confusion to a path of awareness, participation, mutual support, and the preservation of the patient's dignity and independence.