Wired reports on NASA plans to invest in cutting edge medical research. Methods of preventing cancer come first, and "if the astronauts' immunity to radiation cannot be significantly enhanced, then the next step, according to the team, is to grow replacement tissue. They'll begin their research by combining umbilical blood and bone-marrow stem cells with tissues from adults to grow new body tissue in a zero-microgravity environment that mimics conditions in the womb." The article speculates on whether microgravity offers a better environment for tissue engineering of replacement organs - although I should note that work with biodegradable scaffolds here at the bottom of the gravity well has been proceeding apace.
Link: http://www.wired.com/news/space/0,2697,64577,00.html?tw=wn_tophead_2