A large study covering around half of all Sweden’s type 2 diabetes patients found they had a higher risk of developing a number of cancers compared to the general population, but this was not the case for prostate cancer, where type 2 diabetes patients curiously showed a lower risk.

You can read about the study, led by the German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) in Heidelberg, online in the 17 May issue of The Oncologist.

The researchers were interested in the link between cancer and type 2 diabetes, which had already been established in previous studies. There is also a view that the two diseases share risk factors, so for this study they decided to look more closely at which cancers in particular are connected with type 2 diabetes.

For this study, the largest ever to examine cancer risks in people with type 2 diabetes, Dr Kari Hemminki, professor of Molecular Genetic Epidemiology at DKFZ and colleagues from the from the Karolinska Institute and Lund University in Sweden, and also from Stanford University School of Medicine in the US, examined data on 125,126 people in Sweden who had spent time in hospital because of one or more problems connected with type 2 diabetes between 1964 and 2007.

With such a large scale study it was possible for the first time, they said in a statement, to quantify possible links between type 2 diabetes and less common types of cancer.

The data on the type 2 diabetes patients came from the nationwide Hospital Discharge Register, while the cancer data came from the Swedish Cancer Registry.

From these two sources of data the researchers worked out standardized incidence ratios (SIRs) for cancer following the last hospitalization for type 2 diabetes, using the general Swedish population as the comparison group.

Using a link between the cancer register and a multiple-generation register, the researchers were also able to track cancer cases among immediate family members of the patients, thus enabling them to examine what happens to cancer risk when you look at family history of type 2 diabetes.

The results showed that:

  • The type 2 diabetes patients had a higher risk of developing a total of 24 cancers compared to the general population.

  • The highest risk was for pancreatic cancer where it was 6 times higher (SIR 6.08), followed by liver cancer, which was over 4 times higher (SIR 4.25).

  • The elevated risk for cancer of the kidneys, thyroid, esophagus, small intestine and nervous system was more than twice as high for these type 2 diabetes patients than for the general population.

  • The elevated risks were still significant when the researchers only looked at cancer incidence starting five years after hospitalization (to remove the possible effect that being in treatment or moniotoring for one disease makes it more likely that other diseases are spotted earlier).

  • In this case, the highest risk was for primary liver cancer (SIR 4.66).

  • Prostate cancer showed a lower risk in the type 2 diabetes patients compared with the population at large.

  • Patients with a family history of type 2 diabetes showed no exceptional higher cancer risks, apart from their prostate cancer and melanoma risk, which were lower.

The researchers concluded that the findings showed there was an elevated risk for several cancers among these patients hospitalized for type 2 diabetes.

They wrote this could be indicative of “profound metabolic disturbances of the underlying disease”, and that the “lower risk for prostate cancer remains intriguing”.

Speculating about why the risk should be lower for prostate cancer, Hemminki told the media that:

“Possibly, a lower level of male sex hormones in diabetics may be among the factors that are responsible for this.”

“Risk of Cancer Following Hospitalization for Type 2 Diabetes.”
Kari Hemminki, Xinjun Li, Jan Sundquist, and Kristina Sundquist.
The Oncologist, published online May 17, 2010.
DOI: 10.1634/theoncologist.2009-0300

Source: Helmholtz Association of German Research Centres.

Written by: Catharine Paddock, PhD