During the last decade research is gradually repositioning the antimalarial drug chloroquine, and certain related quinoline derivatives, as anticancer agents. Chloroquine and hydroxychloroquine, in particular, have relatively well-characterized toxicity profiles due to several decades of use for treatment of malaria. Previously published review articles provide an excellent overview of the diversity of chloroquine effects on cancer cells, both in the cell culture as well as on human tumors grafted into mice; and an account of the increasing pace of incorporation of hydroxychloroquine in combination treatment schemes for clinical studies. In this review we present some features that are common between cancers that are sensitive to quinoline derivatives, in particular features that are amenable to pharmaceutical intervention.