AimsExploratory analysis of patients' unsolicited written comments in the first 2 years of the Standardisation of Breast Radiotherapy (START) trial quality of life study highlighted a potential effect of non-treatment-related problems on the ratings and interpretation of patient self-reported questionnaires. At 5 years of follow-up all eligible subjects were invited to write comments to further explore these findings. Materials and methodsUsing inductive qualitative methods informed by the exploratory analysis, comments were allocated to relevant themes. Key patient-reported outcome measures (PROMs), clinical and demographic factors were collated for patients who did and did not comment at 5 years and comparisons between the groups explored. ResultsOf 2208 women completing baseline PROMs, 482 proffered comments from 0 to 24 months, forming nine distinct themes, including chronic conditions, life events and psychosocial concerns. At 5 years, 1041/1727 (60.3%) women contributed comments, of whom 500 randomly selected participants formed the sample for analysis. Findings revealed comorbidity, impaired physical functioning and psychosocial problems as key themes, with prevalent adverse effects from local and systemic treatments. Eight new themes emerged at 5 years, including ageing, concerns about future cancer and positive aspects of care. Women commenting were better educated, slightly older and more likely to have had chemotherapy compared with non-commenters. They had significantly worse PROM scores for global health and key quality of life domains relevant to the difficulties they revealed. ConclusionsDifficult personal circumstances and other health concerns affected many women's PROM ratings at 5 years of follow-up, in addition to ongoing cancer treatment effects. Greater attention to multiple sources of distress and adversity could facilitate personalised care and aid interpretation of PROMs.