None of several types of insulin were associated with an increased risk for breast cancer in an international case-control study of women with mainly type 2 diabetes.
After a mean exposure of 3.2 years, there was no difference in the risk for breast cancer among women who received insulin glargine (Lantus, Sanofi) vs insulin aspart (Novolog, Novo Nordisk), insulin lispro (Humalog, Eli Lilly), or human insulin.
"I'm not surprised at the results," Craig Currie, PhD, from Cardiff University, United Kingdom, who was not involved in the study, told Medscape Medical News. "The take-away is that there is no specific individual brand of insulin or insulin analog that is increasing breast cancer specifically."
However, the problem is that this study compares insulin vs insulin, rather than insulin vs other potential glucose-lowering regimens, he added. It is unclear which patients received a combination of insulin, which potentially increases cancer risk, and metformin, which protects against cancer. This research "still leaves open the potential for insulin to increase cancer risk, which I firmly believe it does," he said.
The study by Lamiae Grimaldi-Bensouda, PhD, from LA-SER, Paris, France, and colleagues was published online August 15 in Diabetes Care.
Does Glargine Pose a Breast-Cancer Risk?
Sanofi conducted this study following an alert issued by the European Medicines Agency and the US Food and Drug Administration in July 2009 about a possible increase in cancer in patients who received insulin glargine, based on 4 registry studies.
The current study aimed to assess the relationship between the use of different types of insulin (glargine, aspart, lispro, and human insulin) and the development of breast cancer.
The researchers identified 775 women who were 18 years or older, had been diagnosed with breast cancer between January 2008 and July 2009, and had received oral antidiabetic drugs or insulin for type 1 or type 2 diabetes in the prior 8 years (from 2001, when glargine entered the market, until the 2009 alert about breast-cancer risk).
The women, from 92 centers in the United Kingdom, Canada, and France, were matched, based on several variables, with 3050 control patients with diabetes who were seen in 580 general practices in these countries.
Most women (93.8%) had type 2 diabetes. The women had a mean age of about 53 years old when they were diagnosed with diabetes. About 60% to 65% of the women had received metformin, and about 25% to 26% had received insulin only.
For each type of insulin, women who used insulin did not have an increased risk for breast cancer compared with other women.
Risk for Breast Cancer in the 8-Year Observation Period, Specific Insulin Type vs No Use of That Insulin
| Insulin type | Odds ratio (95% CI) |
| Glargine | 1.04 (0.76 – 1.44) |
| Lispro | 1.23 (0.79 – 1.92) |
| Aspart | 0.95 (0.64 – 1.40) |
| Human insulin | 0.81 (0.55 – 1.20) |
Insulin glargine was not linked with increased risk for breast cancer with different insulin doses, tumor stages, or duration of insulin use.
Risk for Breast Cancer in the 8-Year Observation Period, Glargine vs Other Types of Insulin
| Insulin type | Odds ratio (95% CI) |
| Glargine vs lispro | 0.85 (0.48 – 1.50) |
| Glargine vs aspart | 1.10 (0.64 – 1.89) |
| Glargine vs human insulin | 1.29 (0.78 – 2.13) |
The 8-year period is a relatively short period for cancer latency, the researchers acknowledge, and very few patients were exposed to a specific type of insulin for the whole 8-year period. The study also did not include more recent forms of insulin such as determir (Levemir, Novo Nordisk) or more rarely used insulins such as glulisine (Apidra, Sanofi) or porcine insulin.
They conclude that "this international case-control study, specifically conducted to address the risk of individual insulin use and incident breast cancer after a mean exposure of 3.2 years, found no increased risk with [any] of the individual insulin[s] studied (glargine, lispro, aspart, and human insulin). Longer-term studies are needed to further explore this issue."
Insulin-vs-Insulin Study Leaves Unanswered Questions
"It's a good piece of work; it helps; but it's another one of many" studies of insulin vs insulin, according to Dr. Currie.
"My view is that insulin will be a restricted drug for people with type 2 diabetes in the next 10 years, because of the increase in all-cause mortality and lots of other adverse outcomes," which is shown by quite a bit of work in the pipeline, Dr. Currie continued. "We've missed an opportunity, because a lot of these studies are insulin vs insulin."
However, the research focus may be changing. This September, Dr. Currie will speak about the safety of insulin in type 2 diabetes at a symposium at the European Association for the Study of Diabetes (EASD).
When invited to comment on this study, coauthor Michel Rossignol, MD, scientific and medical director of LA-SER Research, Montreal, Quebec, declined on behalf of the study authors, saying, "Unfortunately, we are not in a position right now to react to the readership or respond to your request before early September."
The International Study on Insulin and Cancer (ISICA) was sponsored by LA-SER and funded by an unrestricted grant from Sanofi. Dr. Grimaldi-Bensouda was the recipient of a research fellowship from INSERM (French National Institute of Health and Medical Research) at the time of the study and is currently employed by LA-SER, the company conducting the study, together with Dr. Rossignol. Disclosures for the coauthors are listed in the article. Dr. Currie has reported no relevant financial relationships.
Diabetes Care. Published online August 15, 2013. Abstract
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