Background The Distress Thermometer is the most widely used rapid screening tool for assessing psychological distress in people affected by cancer. Use of such tools to assess patients emotional and physical needs is a requirement of the NICE guidelines for supportive and palliative care.

Aims To explore the assumption that the Distress Thermometer improves clinicians' understanding of the concerns of people affected by cancer. Two questions were posed: 1. In what settings and with what populations has the Distress Thermometer been used? 2. What evidence concerning validity exists for this tool and what is the strength of evidence?

Methods A systematic review using a framework for mixed evidence (Hawker et al. 2005) across 11 databases. Inclusion criteria: Question 1: papers documenting use of the Distress Thermometer with people affected by cancer, in English, published in peer reviewed journals after 1st January 1998. Question 2: papers (ie, subset of the main search) reporting assessments of the validity of the Distress Thermometer.

Results The authors identified 86 papers reporting use of the Distress Thermometer. Populations included: patients with a specific tumour site, older people, children, adult survivors of childhood cancer, caregivers, relatives/partners of cancer patients and people with new diagnoses and advanced disease. Of 86 papers, 33 examined the validity of the Distress Thermometer, with most comparing the tool with other measures, most commonly the Hospital Anxiety and Depression scale.

Conclusions Although the Distress Thermometer is widely used in cancer supportive and palliative care across a diverse range of settings and in many populations, there is little evidence to support its validity and little is known about what the tool actually measures. Future research must compare the Distress Thermometer with qualitative interviews and the true ‘gold standard’ of asking patients how distressed they feel and what concerns are contributing to that distress.