At some point - as we head into the Millenium - cancer will be cured, other diseases will be cured, etc, etc. In my mind
advances like this and many other medical advances and advancing scientific knowledge will be used in the millenium. I don't necessarily think that the Millenium will come and then automatically all sickness and diseases will be gone. Rather I think our advancing knowledge will be the basis for sicknesses/diseases being gone.