Yes. As a matter of fact, there exists an example of a drug that was given to improve the hemoglobin level so that the anemia from the chemotherapy drugs is alleviated without the need for transfusions, only to find that the drug that improves the blood also makes the cancer grow faster. So that's been the basis for the withdrawal or the black box warning on the use of these drugs.
On March 11th, 2008. See this statement in context.