This open-access article discusses some of the issues in cancer research.

In most ways biology is intermediate between the hard and soft sciences, with all that implies. It’s usually impossible to identify all the confounders, most biologists are not trained in statistics, experiments are complex and you can get different results from slight variations in protocol, we're trying to generalize from imperfect models, many high-profile results don’t get tested by other labs, ... all these factors come together and we get something that people call a “replication crisis.”