"As NPR's Jon Hamilton has reported:
"This drug has generated all kinds of excitement because it is the first approved drug that does more than just relieve the symptoms of Alzheimer's. This drug actually affects an underlying disease process by reducing the amount of sticky amyloid plaque that builds up in the brain. The catch is that removing this plaque may not actually help patients avoid memory loss and thinking problems. One big study showed that it did. Another showed that it didn't.""
In other words, the drug works against what may be a symptom of the disease, but hasn't reliably been shown to do anything for the actual problem.
Science is hard.
Oh, and by the way,
"The drug will be administered through infusions every four weeks, resulting in a yearly cost of about $56,000, the companies said. That's the list price, which doesn't necessarily reflect the out-of-pocket costs for someone who has insurance and/or Medicare. Preliminary estimates suggest patients' copayments for the drug could cost around $11,500 annually."