The following case record did not mention the effect of lithium for the treatment of ADHD on the breast and lung cancer. Given that lithium inhibits GSK-3 beta, it is likely that long-term use of lithium activates canonical Wnt/beta-catenin signal pathway in those cancer tissues.
Would lithium affect the progression of cancer driven by canonical Wnt signal pathway?
http://www.nejm.org/doi/full/10.1056/NEJMcpc1609309