Bipolar disorder and breast cancer can both be found in a list of health problems that begin with the letter "B." But other than that, I'd be hard pressed to find much more that these two diseases have in common.
Surprisingly, though, recent studies have suggested that a breast cancer therapy might also help with bipolar disorder.
Tamoxifen, the most widely prescribed medication for the treatment and prevention of breast cancer, has been available for several decades. Pharmacologists describe it as a "protein kinase C (PKC) inhibitor." That is, tamoxifen prevents or slows down changes in PKC activity. This is important because, during the past few years, several different lines of research evidence have suggested that bipolar disorder may itself be associated with abnormal PKC activity.
One of these studies showed, for instance, that patients with bipolar disorder have higher PKC activity when they are experiencing a manic episode. It is also known that long-term treatment with lithium carbonate and divalproex sodium — both standard bipolar disorder medications — results in more normal patterns of PKC activity.
The clues that bipolar disorder might be associated with an excess of PKC activity led scientists to wonder next if a PCK inhibitor could help in treating bipolar disorder. As it happens, tamoxifen is the only PKC inhibitor available right now for humans.
A new study just published in the Archives of General Psychiatry suggests that tamoxifen does indeed help patients with bipolar disorder when they are experiencing a manic episode. In the study, hospitalized manic patients were given either tamoxifen or a placebo.
After three weeks, the placebo group showed no improvement, whereas the mania symptoms of the group taking tamoxifen had been reduced significantly. One caveat, however: By the end of this relatively short experiment, the tamoxifen-treated patients still had not recovered fully, indicating that longer research trials will be necessary.
This type of research suggests that new medications targeting the PKC system should be developed and then investigated as possible treatments for bipolar disorder.
