HI, I don't think it is Lantus that causes the development of cancer. Possibly the persons affected may have COME OFF METFORMIN. I had Metformin for a decade and was becoming more and more distressed with the gut problems and asked to go onto insulin. This transfer was slow and I had lantus for a year with metformin. As I was started on Novar rapid I elected NOT to keep the Metformin, which is usually maintained with type 2 treatment to help support the insulin. Four months later I found the lump which was confirmed as an early post menopausal breast cancer.(The most common in elderly people) This was easily removed and did not have any evidence of spreading at time of surgery. During the post op discussion to elect which drug I would be offered to help reduce the possible return of the cancer Metformin was offered!!!!
There has been a lot of research on this problem - And I have not,so far, had any relapse despite electing not to continue with any post op drugs, But managing to keep a much more stable blood sugar reading, and so being able to keep well and assist healing
The reasons to develop cancers are very complex. All drugs are monitored, usually in a trustworthy way, so I still trust my Lantus which is giving me a much improved quality of life.