Off label discoveries are always interesting and there is often a great deal of knowledge that is coming with it that are, when they get to understand the mechanisms, good for the pursuit of human biology/neurobiology/pharmacodynamics understanding. On the other hand technology is really pushing forward and I expect to see a reduction of pharmaceutical uses in the next 2 decades. Nanotechnology and the exponential growth of technology itself is promising and it's happening faster than we can think of. There will obviously be a time when human beings will transcend biology.
More's law, singularity, Ray Kurzweil are all good keywords to search to see what we should expect in a near future evolving at that rate. I especially liked The Singularity is Near by Ray Kurzweil.
In case you don't know him I encourage you to read this - http://en.wikipedia.org/wiki/Ray_Kurzweil
Yes this clearly is a clinical breakthrough and one I had not read on. Since chemotherapy although effective has a high toxicity level finding other medications that are safer that would have this effect is crucial. It would be interesting to note how they specifically started researching Prozac for this use, if it was researched specifically or if people who were taking it for depression or other standard usages of it who also were diagnosed with cancer had that go into remission. I do know that many anti-convulsants are used as mood stabilizers and I believe that was how they originally discovered that, in the same manner. It is of note when a medication shows a use that is off label that is completely different from its original use.