The issue of Lantus and cancer has been around a long time. Your article just points to a recent Swedish study which showed a cancer risk higher than previously reported. The article also says:
Study Flaws
The Swedish study released yesterday was too small and had flaws that make it impossible to definitively address any potential risk from Lantus, said Riccardo Perfetti, vice president for medical affairs at Sanofi Diabetes in Paris. The company is researching the question, with more robust results expected by the end of the year, he said.
“I find it surprising that today after so many scientific reports on this topic, we’re still discussing these very small studies,” he said. “Patients using insulin may be compared to patients not using insulin, which might be a gigantic methodological mistake. People using insulin are usually much older and have been diabetic for many years.”
Because almost all cats are on Lantus for a very short time compared to humans, I would not be concerned.