Identification of factors associated with cancer related fatigue syndrome in disease-free breast cancer patients after completing primary treatment.

This study is an analysis of variables associated with women who meet the criteria for after completion of successful primary treatment for breast cancer. This analysis was conducted to identify factors independently associated with cancer related fatigue syndrome using a combined dataset from two non-overlapping studies conducted on similar populations. Participants who were clinically (and radiologically) disease-free, between 3 months and 2 years after treatment, were recruited from a single centre. A diagnostic interview was conducted to ascertain whether they met the criteria for cancer related fatigue syndrome. We analysed a number of treatment, laboratory and questionnaire variables between groups. Those that were significantly different were entered into a logistic model. A total of 278 subjects (105 cases of cancer related fatigue syndrome and 173 controls who did not meet the criteria) were analysed. A number of questionnaire responses were significantly different including all of the European Organisation for the Research and Treatment of Cancer core 30 item quality of life questionnaire (EORTC QLQ c30) and Breast questionnaire 23 item subgroup scores. 11 variables were entered into the final model and 5 were independently associated with cancer related fatigue syndrome: Hospital anxiety and depression scale score, EORTC pain and insomnia scales, breast systemic side effects and plasma sodium. There was, however, no association with demographic or treatment variables. As a conclusion, cancer related fatigue syndrome after treatment is linked with sub-clinical mood pain and subjective sleep disturbance and with the side effects of systemic treatment. This study is unable to determine whether these associations are causal, but they provide a potential target for interventions to manage the symptoms of cancer related fatigue syndrome.