Background and aims: Family caregivers play an important role in assisting their family members with cancer, but their influence on the treatment decision‐making process has not yet been adequately investigated. This exploratory study approached this topic via reconstructive methodology, focusing on assessing patient‐caregiver relationships. Methods: We conducted semi‐structured interviews with 37 mostly elderly cancer patients (median age: 74 years) about the context of their diagnosis, treatment decision, and family support. Additionally, we interviewed 34 caregivers of cancer patients. Of these, 25 were related to patients interviewed. We analyzed the interviews via a multi‐step coding method informed by Grounded Theory methodology toward characterizing patient‐caregiver relationships, the treatment decision‐making process, and the caregivers' role therein. Results: In the majority of cases (86%), patients were being supported by caregivers. We categorized patient‐caregiver relationships in regards to the caregivers' involvement in the therapy decision‐making process. We found patient‐caregiver interaction patterns that indicate the potential of caregivers to decidedly influence the therapy decision‐making process. Yet, only in 38% of cases, a caregiver attended relevant patient‐physician‐consultations. Conclusion: Depending on the nature of the patient‐caregiver relationship, the traditional concept of shared decision‐making, which assumes a dyadic relationship, needs to be extended toward a more dynamic concept in which caregivers should be involved more frequently. This could enable physicians to better understand a patient's reasons for or against a therapy proposal and ensure that the patient's wishes are communicated and considered. On the other hand, strong caregiver‐involvement bears risks of over‐stepping elderly patients' wishes, thus violating patient autonomy.