I came to the biological sciences trained as a chemist. As I began working on my Ph.D. and variously encountered papers on cell signaling research (the field that much "cancer research" would fall into) it was blindingly apparent to me, perhaps because of my chemistry background, what was going on...
Cell Signaling (and much of Biology) research is in its Alchemy phase. Now, alchemy often gets a bad rap as being completely worthless, snake-oil type stuff, but this was not the case at all. Rather, individuals were working on an area about which almost nothing was known, and (more importantly) for which the key central organizing laws were not yet revealed (for Alchemy: the atomic theory of matter and chemical bonding, for Cell Signaling: how individual proteins and small molecules interact). Furthermore, the goals were lofty and almost certainly unattainable (for Alchemy: turn base metals into gold, for Cell Signaling: cure cancer), driving people to do "rush" work. It's not that the results are completely invalid, or that the experiments are useless. It's just that everyone feels like they're so close to a solution (Alchemists were way off with Phlogiston, and I'll bet Cell Signaling researchers are similarly clueless as to what really matters) that no one takes the time to step back and synthesize the results in an attempt to understand the forest from the trees.
Cell Signaling will, eventually, have its Joseph Priestley, its Dmitri Mendeleev.
From experience, the fact that 89% of these "cancer research" papers are not reproducible almost definitely has less to do with fraudulent data and so much more to do with crazy complex experimental setups that end up probing a half-dozen experimental variables all at once (without the researchers even grasping that this is going on).
Yeah, publish or perish sucks, but what sucks more is the death of basic science research. The Alchemists eventually became Chemists because they refocused on core principles (atomic theory, bonding) and forgot about the lofty goals (turn lead into gold)...
...but try telling any politician that they should decrease cancer research funding and refocus on genetics, structural biology, and evolution research. I'd love to know how they respond.