A new study has reported that long-term use of insulin glargine (Lantus) may increase risk of breast cancer, especially among women who were already using insulin before starting Lantus. Lantus is a long-acting insulin analog used by both type 1 and type 2 diabetics to help control blood sugar throughout the day.

The author used the UK’s General Practice Research Database to identify 15,227 women aged at least 40 years with type 2 diabetes who were treated with insulin during the period 2002-2006. The women were followed until first breast cancer diagnosis or year-end 2009. Users of Lantus were matched with users of other insulins based on age, calendar date and duration of prior insulin use. The study included 4,579 Lantus users and 10,648 users of other insulins.

A total of 246 of the women in the study developed breast cancer during the follow-up period, which lasted up to eight years. Lantus use was not found to be associated with increased risk of breast cancer during the first five years of use. However, the risk tended to increase after the first five years, especially for women who were already using another type of insulin before starting Lantus. Such women had 2.7 times the breast cancer risk of non-Lantus users. The authors conclude that risk of breast cancer in women with type 2 diabetes is not increased during the first five years of Lantus use. However, longer-term use may increase this risk, particularly in women with longstanding use of insulin before starting Lantus.

Please see our article on type 2 diabetes and breast cancer for more information on the links between diabetes and breast cancer.