. >> this is ground zero for the polycythemia vera cancer investigation. >> called pv for short, polycythemia vera is a rare form of blood cancer in most of the u.s. but here, there's a confirmed cluster of pv cases. >> in 2004, we learned that there were 67 diagnosed cases of polycythemia vera, which ultimately led to the--to the confirmation of a cancer cluster. since then, 130 cases of polycythemia vera have been reported to the pa cancer registry. >> people with pv, like debra trently and merle wertman, suffer from an overproduction of red blood cells. >> so the blood gets very thick, and it can cause, you know, blockages to smaller blood vessels that feed vital organs of our body. tissue death can occur anywhere in the body. it can occur in their brain, it can occur in their toe, it can occur in their liver. we've seen patients where they've developed infarctions to their feet, where they've had to have toes amputated. they have infarctions to their liver. they can have an infarction to their heart, much like a heart attack. >> the way it works on you, you're so exhausted and tired, you