I had a benign tumor removed from my brain in '98. It was about the size of a tennis ball. I'm very fortunate. The removal seems to have caused no ill effects. I'm still able to operate at pre-surgery levels. At about the time we discovered my problem Dan Quizenberry, former closer for the Royals, was diagnosed with a "level 4" malignant brain tumor.
My tumor was basically a floating mass that was putting pressure on the surrounding brain tissue. Quiz's had roots that were growing agressively into other parts of his brain.
Bottom line - I'm still here with a large hole in my head and the Quiz is gone (may he rest in peace).
They are not giving the location of Giambi's tumor, but my guess based upon his weight loss, is it is in his digestive system. I was off work for about four weeks following my ordeal, but then I'm not a professional athlete. I would guess that Giambi could conceivably be back before the end of the season, but wouldn't expect much production.
As someone said earlier, the main thing here is Giambi's health. Some things (there aren't many) are just more important than baseball.