UNICANCER: French prospective cohort study of treatment-related chronic toxicity in women with localised breast cancer (CANTO)

Background Corresponding with improved survival among patients with breast cancer, the awareness of the long-term effects of cancer treatments has increased. CANcer TOxicities (CANTO) aims to identify predictors of development and persistence of long-term toxicities in patients treated for stages I-III breast cancer and to characterise their incidence, as well their impact. In this paper, we describe the methodology used in this study and provide a first characterisation of the study population. Methods CANTO (NCT01993498) is a French prospective, longitudinal cohort study enrolling patients with invasive cT0-cT3cN0-3M0 breast cancer of 26 French cancer centres. Patients are assessed at diagnosis, 3-6 (M0), 12 (M12), 36 (M36) and 60 (M60) months after completion of primary surgery, chemotherapy or radiotherapy whichever comes last. CANTO collects clinical, treatment, toxicity data, an extensive list of validated patient-reported outcomes (focusing on quality of life, psychological and behavioural questionnaires) and ad hoc socioeconomic questionnaires. Blood collection is performed at diagnosis, M0, M12, M36 and M60. Biologic sub-studies are ongoing (eg, microbiotic and cognitive sub-study). Results Enrolment started in 2012; by October 2018, 12 012 patients had been enrolled. Data collected have a low missing completion rate (<5% for key clinical variables, <20% for patient-reported outcomes). Blood, serum and plasma samples are stored in over 96% of patients. Among the first 5801 patients enrolled in CANTO, 76.7% of patients had hormone receptor positive and human epidermal growth factor 2 negative tumours; 73.1% of patients had breast conserving surgery; 90.4% received adjuvant radiotherapy, 53.4% (neo) adjuvant chemotherapy, 11.3% adjuvant trastuzumab and 80.3% adjuvant hormonotherapy. Conclusions CANTO represents a unique opportunity to explore important medical, biological and psychosocial outcomes on breast cancer survivor population.