FRIDAY, May 19, 2017 (HealthDay News) -- Rare cancers account for one in five cancers diagnosed in the United States, presenting special challenges to doctors and patients, a new study shows.
"Continued efforts are needed to develop interventions for prevention, early detection, and treatment to reduce the burden of rare cancers," said researchers led by Carol DeSantis, an epidemiologist with the American Cancer Society.
"Such discoveries can often advance knowledge for all cancers," the team added in a cancer society news release.
A rare cancer is 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.
These infrequently seen cancers can be tougher to diagnose because most research focuses on more common cancers, and they're tougher to treat for the same reason, the researchers said.
"There is less preclinical research and fewer clinical trials for rare cancers, which are often limited to select high-volume cancer centers" they wrote.
Their analysis found that rare cancers make up almost one-quarter of cancers diagnosed in Hispanics and 22 percent of cancers in Asian/Pacific Islanders. The rates for blacks and whites were 20 percent 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.
Also, 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 percent versus 75 percent.
Children, however, have a better shot at survival than seniors. More than eight in 10 children and teens with rare cancers survive five years compared to less than half of older adults (aged 65 to 79) with rare cancers, the study found.
The study was published May 19 in CA: A Cancer Journal for Clinicians.
Cancer Research UK has more on rare cancers.