Dec. 16, 2014 -- People with type 1 or type 2 diabetes are diagnosed with more of some types of cancer -- and are more likely to die from cancer -- than people without diabetes, a new Australian study shows.
The researchers say that close follow-up, given right after a diabetes diagnosis, might partly explain the increased cancer risk seen. But these factors "do not explain increased risks 2 years following diabetes diagnosis, particularly for cancers of the pancreas, liver, kidney, and endometrium."
Based on the findings, the researchers say, people with diabetes should get screened for cancer, which could help doctors treat cases early and lessen premature deaths due to cancer.
The research is published online in the journal Diabetes Care.
The study included 953,382 registrants from the National Diabetes Service Scheme (NDSS) in Australia: 80,676 with type 1 diabetes and 872,706 with type 2 diabetes, diagnosed between the years 1997 and 2008.
The NDSS is one of the world's largest diabetes registries, and the data were linked to Australia’s National Death Index. This information was then linked to data from the Australian Cancer Database. Cancer rates in Australia's general population served as a comparison.
Lead researcher Jessica Harding, of the Baker IDI Heart and Diabetes Institute in Melbourne, says that with the aging population and increasing obesity, the number of new cases of cancer and diabetes are on the rise. Given that these increases are happening over the same time periods, she and her colleagues figured there must be a link between the two.
The highest excess risks the researchers saw were for cancers of the pancreas, liver, endometrium, kidney, thyroid, and gallbladder, and for a cancer that affects blood cells and bone marrow called chronic myeloid leukemia.
Also, she says, "given that insulin…may promote the growth of cancer cells, we wanted to explore whether type 1 patients -- treated with insulin -- had a higher risk for cancer compared with type 2 patients.
"In particular, are rising glucose [blood sugar] levels and/or obesity in diabetes leading to the development of cancer? Such theories are supported by animal data, but large studies on human populations are lacking," she says.
Excess Risk of Cancer in Both Type 1 and Type 2 Diabetes
Among females with type 1 diabetes, there were increased cancers of the pancreas, liver, esophagus, colon and rectum, stomach, thyroid, brain, and lung, as well as ovarian and endometrium cancer compared with the general population.
For men, a similar pattern was seen. However, there were fewer cases of prostate cancer, and the link between the various cancers and diabetes was not as significant.
Higher death rates were seen for cancers of the pancreas and liver, and non-Hodgkin's lymphoma, among those with type 1 diabetes, and for cancers of the kidney (in males only) and, in women, for brain and endometrial cancers.
The highest risks were seen in cancers of the liver and pancreas.
Higher death rates were found for cancers of the pancreas, liver, and kidney, and Hodgkin's lymphoma. In females only, a greater death rate was also found for stomach and gallbladder cancer, and non-Hodgkin's lymphoma.
The researchers say that because of the massive size of the study, they couldn't explore the extent to which risk factors like obesity, smoking, and diabetes treatment might impact the diabetes-cancer link. But previous studies of type 2 diabetes looking at those factors still found higher risks for a number of cancers, they say.
"Therefore, it is unlikely that these factors explain the entire association between diabetes and cancer."
Is High Blood Sugar the Driving Cause?
It's not likely that insulin is the driving force behind the cancers, the researchers say.
Instead, they suggest that high blood sugar, which doctors call hyperglycemia, may be a contributing factor.
The study also explored the relationship between diabetes and cancer at different time periods after a diabetes diagnosis.
"Cancers diagnosed many years after diabetes diagnosis are more likely to have occurred as a consequence of diabetes," Harding says.