1. ¹Section of Epidemiology, Brookes Lawley Building, Institute of Cancer Research, Sutton, Surrey SM2 5NG, UK
2. ²Strathclyde Diabetic Group, Victoria Infirmary, Glasgow G42 9TY, UK
3. ³Heart of Birmingham Diabetes Care, Handsworth, Birmingham B1 3AS, UK
4. ⁴Department of Oncology, University of Leicester, Leicester LE1 6TP, UK
5. ⁵Department of Epidemiology and Public Health, University of Leicester, Leicester LE1 6TP, UK
6. ⁶Scottish Study Group for the Care of Diabetes in the Young, University of Aberdeen Medical School, Aberdeen AB25 2ZD, UK
7. ⁷Royal College of Physicians of Edinburgh Group, Ninewells Hospital & Medical School, Dundee DD1 9SY, UK
8. ⁸Department of Diabetes, Poole Hospital NHS Trust, Dorset BH15 2JB, UK
9. ⁹Barts Oxford Study Group, Medical School Unit, Southmead Hospital, Bristol BS10 5NB, UK
10. ¹⁰Department of Epidemiology & Public Health, Queen's University, Belfast BT12 6BJ, UK
11. ¹¹8 Kingsfield Road, Oxhey WD19 4T, UK

Correspondence: Professor AJ Swerdlow, E-mail: anthony.swerdlow@icr.ac.uk

Received 22 February 2005; Revised 4 April 2005; Accepted 4 April 2005; Published online 10 May 2005.

Abstract

Raised risks of several cancers have been found in patients with type II diabetes, but there are few data on cancer risk in type I diabetes. We conducted a cohort study of 28 900 UK patients with insulin-treated diabetes followed for 520 517 person-years, and compared their cancer incidence and mortality with national expectations. To analyse by diabetes type, we examined risks separately in 23 834 patients diagnosed with diabetes under the age of 30 years, who will almost all have had type I diabetes, and 5066 patients diagnosed at ages 30–49 years, who probably mainly had type II. Relative risks of cancer overall were close to unity, but ovarian cancer risk was highly significantly raised in patients with diabetes diagnosed under age 30 years (standardised incidence ratio (SIR)=2.14; 95% confidence interval (CI) 1.22–3.48; standardised mortality ratio (SMR)=2.90; 95% CI 1.45–5.19), with greatest risks for those with diabetes diagnosed at ages 10–19 years. Risks of cancer at other major sites were not substantially raised for type I patients. The excesses of obesity- and alcohol-related cancers in type II diabetes may be due to confounding rather than diabetes per se.