Promacta does not cause cancer, but it can worsen a precancerous blood condition called myelodysplastic syndrome (MDS) and cause it to develop into acute myelogenous leukemia (AML), a type of blood cancer. For this reason, people with MDS or with any type of pre-existing blood cancer should not take Promacta. But there is no evidence of an increased risk of cancer when Promacta is used by people without MDS or a blood cancer.