BACKGROUND: Patients' quality of life has become a major objective of care in oncology. At the same time, it has become the object of increasing interest by researchers, working with both quantitative and qualitative methods. Progress in oncology has enabled more patients to survive longer, so that cancer is increasingly often a chronic disease that requires long-term treatment that can have negative effects on patients' quality of daily life. Nonetheless, no qualitative study has explored what patients report affects their quality of daily life during the treatment period. This study is intended to fill this gap. METHODS: We conducted a multicenter qualitative study based on 30 semi-structured interviews. Participants, purposively selected until data saturation, had diverse types of cancer and had started treatment at least 6 months before interview. Data were examined by thematic analysis. RESULTS: Our analysis found two themes: (1) what negatively affected for patient's quality of daily life during the treatment period, a question to which patients responded by talking only about the side effects of treatment; and (2) what positively affected their quality of daily life during the treatment period with three sub-themes: (i) The interest in having -investing in - a support object that can be defined as an object, a relationship or an activity particularly invested by the patients which makes them feel good and makes the cancer and its treatment bearable, (ii)The subjective perception of the efficacy of the antitumor treatment and (iii) the positive effects of relationships, with friends and family, and also with their physician. CONCLUSIONS: Patients must be involved in their care if they are to be able to bear their course of treatment and find ways to endure the difficult experience of cancer care. The support object represents an important therapeutic lever that can be used by their oncologists. They should be interested in their support objects, in order to support the patients in this investment and to help them to maintain it throughout the health care pathway. Furthermore, showing interest in this topic, important to the patient, could improve the physician-patient relation without using up very much of the physician's time.