BARCELONA – A large Swedish national registry study has found no hint of increased cancer risk in bipolar patients on long-term lithium therapy.
“This is a very important null result. There is no increased risk for cancer for bipolar patients on lithium. It’s a bad rumor. It’s important to tell patients we’re very confident this is true. We studied every single type of cancer. We would have seen something here if there was something to see,” Lina Martinsson, MD, PhD, said at the annual congress of the European College of Neuropsychopharmacology.
Using comprehensive registry data on nearly 2.6 million Swedes aged 50-84 years with 4 years of follow-up, including 2,393 patients with bipolar disorder on long-term lithium and 3,049 patients not on lithium, the overall cancer incidence rate was 5.9% in the group on lithium and 6.0% in those not taking the drug. Those rates were not different from the general Swedish population, reported, a senior psychiatrist at the Karolinska Institute in Stockholm.
Such patients had a 72% greater risk of lung cancer and other cancers of the respiratory system than the general population, a 47% increased risk of GI cancers, and a 150% greater risk of endocrine organ cancers.
“The increase in respiratory and digestive organ cancers might depend upon bipolar patients’ tendency for smoking and other types of hard living. We can’t explain the increase in endocrine cancers,” she said.
In contrast, the rates of these types of cancer were no different from the general population in bipolar patients taking lithium, hinting at a possible protective effect of the drug, although this remains speculative, the psychiatrist added.
The question of whether lithium is associated with increased cancer risk has been controversial. In particular, several groups have reported a possible increased risk of renal cancer on the basis of what Dr. Martinsson considers weak evidence. She felt a responsibility to undertake this definitive Swedish national study examining the issue because the cancer speculation arose following her earlier study demonstrating that bipolar patients on lithium had much longer telomeres than those not on the drug, and that the ones who responded well to lithium had longer telomeres than those who did not (Transl Psychiatry. 2013 May 21. d).
“If longer telomere length gives longer life to the wrong cells, it might enhance the risk of cancer,” she noted.
But this theoretical concern did not hold up under close Swedish scrutiny. “Warnings for cancer in patients with long-term lithium treatment are unnecessary and ought to be omitted from the current policies,” Dr. Martinsson said.
She reported no financial conflicts regarding her study, which was funded by the Swedish Research Council.