Abstract Patient-reported outcomes (PROs) offer a non-invasive, low-cost way to capture patients’ symptoms, functioning, and quality of life. Yet, their potential as early indicators of tumor size, recurrence/disease progression, and survival remains unclear. We retrospectively analyzed 445,239 longitudinal PRO entries from 2738 patients with breast cancer, pooled from four clinical trials, including both early- and late-stage disease, covering 15 PRO measures.