To address unresolved questions about drug safety and efficacy at the time of approval, the European Medicines Agency (EMA) may require that manufacturers conduct additional studies during the post-marketing period. As a growing proportion of new cancer drugs are approved on the basis of limited evidence of clinical benefit, timely completion of post-marketing requirements is important. We used publicly-available regulatory documents to evaluate key characteristics of pivotal studies supporting EMA-approved cancer drugs from 2004-2014 and assessed completion rates of post-marketing data collection requirements after a minimum of 5 years. From 2004-2014, 79% (45/57) of EMA-approved cancer drugs had to fulfill post-marketing requirements. Pivotal trials supporting the approval of cancer drugs with post-marketing requirements were less likely to have randomized designs (41/61, 67% vs 11/11, 100%), include an active comparator (20/61, 33% vs 10/11, 91%), or measure overall survival as the primary study endpoint (18/61, 30% vs 6/11, 55%) compared to pivotal trials for drugs without post-marketing requirements. Among 200 post-marketing requirements, almost half were designed to assess drug safety. After a minimum of 5 years, 60% (121/200) of requirements were completed, 10% (19/200) were ongoing, and 30% (60/200) were delayed. About half (40/75, 53%) of post-marketing requirements for new clinical studies were completed on time. Delays in the completion of post-marketing requirements often did not impact the likelihood of drugs receiving permanent marketing authorization (87%, 39/45) after 5 years. Our findings highlight the need for EMA to better enforce its authority to require timely completion of post-marketing requirements and studies.