Rare diseases represent a group of conditions affecting a very limited number of patients. Low profitability resulting from the small size of target population coupled with difficulties in conducting the research causes the lack of interest from the pharmaceutical industry. In order to promote research and development of medicines for rare diseases, a special ‘orphan’ legislation was introduced in a number of regions. These measures led to a significant increase in the number of approved orphan molecules. The high per patient cost of orphan drugs, as well the rapid growth of orphan drug sector, raised concerns regarding the sustainable funding of therapies for rare diseases. Rare cancers represent the majority of the current orphan drug market and are often associated with very high revenues. This chapter provides a review of orphan legislations and health technology assessment framework, analyses the position of oncology drugs on the orphan drug market and discusses future perspectives.