Type 2 diabetes ("diabetes"), a disease characterized by abnormally high levels of glucose in the blood, is associated with poorer survival among women with breast cancer. One study reported that breast cancer patients with high fasting blood sugar levels at diagnosis were almost twice as likely to experience a recurrence as patients with normal levels. Generally speaking, diabetics who use metformin have better outcomes than those who do not. On the other hand, there is some evidence that use of Lantus (insulin glargine) or sulfonylurea derivatives such as Glipizide could reduce breast cancer-specific survival, although these findings are controversial. Now a new study has reported that the risk of recurrence among diabetics is greatest in those using insulin.

Latest research finds diabetics using insulin have highest recurrence risk

The study referenced at the beginning of this news article was designed to investigate the influence of type 2 diabetes and diabetes medications on the risks of second breast cancer events (breast cancer recurrence or second primary breast cancer) and death. The study included 4,216 women diagnosed with early-stage breast cancer (defined as stage 1 or stage 2) for whom data was collected concerning diabetes and associated medications (insulin, metformin, and sulfonylureas). A total of 610 of the women had diabetes, of whom 76% used oral diabetes medications and/or insulin. The women were followed for a median of 6.3 years.

A total of 13% of the women experienced second breast cancer events during follow up. The risk of recurrence was 57% higher among women with diabetes compared to non-diabetics. However, the findings were inconclusive for second primary breast cancers. When considering only the women with diabetes, insulin use was found to be associated with almost twice the risk of recurrence (1.94 times) and more than twice the risk of death from all causes (2.33). On the other hand, metformin use was associated with just over half the risk of death from all causes (0.55). The authors conclude that there is an association between diabetes and increased risk of recurrence, and this risk may be greater among insulin users. Metformin appears to reduce all-cause mortality among breast cancer survivors. Further research in larger, more diverse populations is warranted, according to the authors.

Please see our article on type 2 diabetes for more information.