(HealthDay News) — Rare cancers account for one in five cancers diagnosed in the United States, presenting special challenges to doctors and patients, according to research published online May 19 in CA: A Cancer Journal for Clinicians.

A cancer is considered rare when it’s one that’s diagnosed in fewer than six cases per 100,000 people a year. Overall, the analysis of national cancer data showed that 20 percent of all cancers are rare cancers. Rare cancers make up 24 percent of cancers diagnosed in Hispanics and 22 percent of cancers in Asian/Pacific Islanders. The rates for blacks and whites are 20 and 19 percent, respectively. The researchers also found that 71 percent of cancers in children and teens are rare, compared with less than 20 percent of cancers diagnosed in adults 65 and older.

Rare cancers tend to be diagnosed at a later stage, and the five-year survival rate for adults with unusual cancers is lower than for other cancers. In men, for example, the rates are 55 versus 75 percent. However, 82 percent of children and teens with rare cancers survive five years, compared to 46 percent of older adults (aged 65 to 79) with rare cancers, the investigators found.

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“Continued efforts are needed to develop interventions for prevention, early detection, and treatment to reduce the burden of rare cancers,” the authors write. “Such discoveries can often advance knowledge for all cancers.”

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