Rare cancers in Japan: definition, clinical features and future perspectives.

This review introduces the definition, epidemiology and therapeutic challenges of rare cancers and describes the establishment of the Rare Cancer Center at the National Cancer Center, Japan. Rare cancers are defined as malignant tumors with an incidence rate of less than 6 cases per 100 000 individuals. Due to their low incidence rate, medical treatment for rare cancers is more challenging than for more common cancer types. Specifically, 190 types of cancers, including bone and soft tissue sarcomas, gastrointestinal stromal tumors (GISTs), neuroendocrine tumors and gliomas, are classified as rare cancers. Individually, each of the rare cancers accounts for less than 1% of all cancers, but collectively they account for 15% of all cancers. On the basis of their medical management, rare cancers can be subclassified into two types: Type I (rare cancers within cancer-rare organs) and Type II (rare cancers within cancer-common organs). Most importantly, the outcomes for rare cancers are poorer compared to those of common cancers. In 2014, the Rare Cancer Center was established at the National Cancer Center to address the various challenges related to rare cancers. The Rare Cancer Center has adopted a multifaceted approach for overcoming these challenges, including active sharing of information through a dedicated website and an online seminar series 'Rare Cancer Meet the Expert', providing medical support through telephone consultations via a 'Rare Cancer Hotline', supporting basic research and establishing the 'MASTER KEY Project' aimed at developing new treatments.