Diabetics have increased breast cancer risk, new study reports
According to a new study presented at the 34th Annual San Antonio Breast Cancer Symposium on December 7, diabetes is associated with a 40% increased risk of breast cancer. A case-control study, which extracted data from Sweden's extensive birth-to-death population registry and a national prescription registry revealed that diabetes was associated with a nearly 40% increase in risk for breast cancer, noted Hakan Olsson, MD, a professor in the departments of oncology and cancer epidemiology at Lund University in Lund, Sweden. He noted, "There is a link between diabetes and breast cancer even after adjusting for obesity and abnormal blood lipids, especially seen within four years of a cancer diagnosis.”
Dr. Olsson and his team also found a significant association between overall cancer risk among patients with diabetes who used the long-acting insulin analogue insulin glargine (Lantus; Sanofi Diabetes). In contrast, the oral antidiabetic agent metformin was associated with a trend toward lower cancer risk among diabetics; however, this finding was not statistically significant. The insulin findings, contradicted those of a meta-analysis also presented December 7 at the International Diabetes Federation (IDF) World Diabetes Congress 2011 in Dubai, United Arab Emirates. That study, which included data from observational studies and randomized, controlled trials, found no additional cancer associated with the use of glargine.
Beyond a relationship to insulin, the evidence for a link between diabetes and breast cancer risk appears to be strong, noted Jennifer Ligibel, from the Division of Breast Oncology at the Dana Farber Cancer Institute in Boston, Massachusetts. She said, "I think this work is very important as we try to better understand the relationship between obesity, which is unfortunately a growing health problem here in the US and around the world, and its link to cancer.”
Dr. Ligbel noted that the MA 32 study, a phase 3 randomized trial of metformin vs. placebo in early-stage breast cancer, is recruiting patients in the U.S and Canada. The researchers will examine whether metformin may interfere with the growth of early breast cancer and whether it could be combined with other therapies to reduce the incidence of recurrence.
Dr. Olsson and his colleagues reviewed data on 2,724 case-patients with cancer and 20,542 controls (matched for age, sex, and residence) from outpatient and inpatient population-based registries; this was done to evaluate the relationship between cancer, diabetes, obesity, and/or abnormal blood lipids. They also evaluated data regarding insulin glargine and metformin use from the Swedish pharmacy prescription registry. A total of 202 case-patients and 1,297 controls had used glargine; 1,036 case-patients and 7,039 controls had used metformin.
The researchers found that for the time interval of 90 to 1,460 days before a breast cancer diagnosis, diabetes was associated with an increased risk for breast cancer. Neither obesity nor lipid abnormality was significantly associated with breast cancer risk over the same period.
Although their follow-up method did not allow them to look at specific cancer types, the Swedish researchers analyzed overall cancer risk among glargine and metformin users and found that glargine was associated with an increased risk, whereas metformin was associated with a non-significant trend toward lower risk.
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