Oncology is one of the areas of medicine with the most active research being conducted on new drugs. New pharmacological entities frequently enter the clinical arena, and therefore, the safety profile of anticancer products deserves continuous monitoring. However, only very severe and (unusual) suspected adverse drug reactions (ADRs) are usually reported, since cancer patients develop ADRs very frequently and some practical selectivity must be used. Notably, a recent study was able to identify 76 serious ADRs reported in updated drug labels of oncologic drugs and 50% of them (n = 38) were potentially fatal. Of these, 49 and 58%, respectively, were not described in initial drug labels. The aims of this article are to provide an overview about spontaneous reporting of ADRs of oncologic drugs and to discuss the available methods to analyze the safety of anticancer drugs using databases of spontaneous ADR reporting.