Current status and perspectives of patient-derived rare cancer models.

Malignancies with extremely low incidences, such as less than 6 per 100,000 people annually, are defined as rare cancers. Approximately 200 malignancies are classified in this category, therefore the total number of patients with rare cancers is greater than that of patients with any single common cancer. However, because of the small numbers of patients, novel therapies have not been developed for individual rare cancers, and clinical outcomes remain dismal. Patient-derived cancer models are indispensable for both basic and pre-clinical studies, and their roles will increase in the era of post-genome medicine. Although patient-derived cancer models have long been used in oncology, they are not well developed for rare cancers. In the context of sarcoma, the presently available cell lines and xenograft models are limited and do not satisfy the needs of research. Indeed, the lack of effective therapies for rare cancers might be attributable to the paucity of adequate patient-derived cancer models for pre-clinical studies. To facilitate the establishment and availability of patient-derived rare cancer models, we need to create effective methods for model establishment, share the valuable clinical samples and established models, and implement guidelines to record the clinical data of donor patients and original tumors. Patient-derived rare cancer models are a public resource, and they should not be used exclusively but should rather be shared among the research community.