People who undergo pancreatic irradiation during childhood cancer therapy are at an increased risk for developing diabetes later in life, report researchers.
However, they are only at significant risk for developing the condition after the age of 20 years, highlighting the importance of long-term follow up of childhood cancer survivors, say Florent de Vathaire (INSERM, Paris, France) and colleagues.
The findings come from a retrospective analysis of questionnaires and medical records for 2520 childhood cancer survivors who were followed up for a mean of 28 years.
As reported in The Lancet Oncology, 65 of the study population developed diabetes.
Of the 888 patients who had not received radiotherapy, five (1%) developed the condition compared with 60 (4%) of 1632 people who did receive radiotherapy.
The relative risk for diabetes was 11.5 in patients who received a 10 Gy dose or more to the tail of the pancreas and this risk became greater with an increasing radiation dose of up to 20-29 Gy, after which the risk plateaued.
The cumulative incidence of diabetes at the age of 45 years reached 16.3% in patients who had received more than 10 Gy to the tail of the pancreas.
The radiation dose to other parts of the pancreas did not have a significant effect, a finding that can be explained by the fact that the concentration of islets of Langerhans is higher in the tail than in the body and head of the pancreas, says the team.
The researchers also found that children who were younger than 2 years old at the time of radiotherapy had a significantly increased risk for developing diabetes than patients who were older when they underwent therapy, with a relative risk for 2.1 versus 1.4 for 1 Gy of treatment.
"To our knowledge, this study provided the first estimation of a dose-response between radiation dose to the tail of the pancreas and the risk of subsequent diabetes mellitus," write Vathaire et al. "Our findings emphasise the need to test for glucose tolerance in all patients with a history of abdominal radiation therapy to enable the early detection of diabetes."
The results also highlight the need for contouring of the pancreas when planning radiation therapy, to achieve as low as possible radiation dose to the organ, they add.
In an accompanying comment, Kevin Oeffinger from Memorial Sloan-Kettering Cancer Center in New York, USA, says further study is needed to clarify the mechanisms underlying diabetes after abdominal radiation.
"Understanding these mechanisms will, hopefully, result in the development of targeted interventions that will lead to a reduction in risk in this population," he remarks.
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