About one in five cancer diagnoses in the United States is a rare cancer, according to a new American Cancer Society report.
The report, appearing in a peer-reviewed journal of the American Cancer Society, also finds that most child cancers (more than two thirds) are rare.
And given the lack of research on these conditions, most take a long time to diagnose, and once it is spotted, the disease is very advanced.
Researchers say the rate of rare cancers is set to increase on paper – mainly down to better testing methods which can classify cancers.
However, they said the number of treatment methods and clinical trials is not picking up at the same pace – meaning survival rates are still low.
Researchers from the American Cancer Society say the rate of rare cancers is set to increase on paper – due to to testing methods which can classify cancers. But survival rates remain low
A rare cancer is defined as affecting fewer than six per 100,000 people per year.
For most rare cancers, research on causes, prevention or early detection is either limited or nonexistent.
These diseases can also be difficult to diagnose, meaning the disease tends to be advanced by the time they reach a conclusion.
Treatment optionsare often more limited and less effective than for more common cancers, partly because there is less preclinical research and fewer clinical trials for rare cancers.
And there are limited published data on the burden of rare cancers in the United States.
Dr Carol E. DeSantis led a team using data from the North American Association of Central Cancer Registries and the Surveillance, Epidemiology, and End Results (SEER) program.
From there, they comprehensively examined current incidence rates, stage at diagnosis, and survival for more than 100 rare cancers in the United States.
They found overall, approximately 20 percent of patients with cancer in the United States are diagnosed with a rare cancer.
Rare cancers make up a larger proportion of cancers diagnosed in Hispanic (24 percent) and Asian/Pacific Islander (22 percent) patients compared with non-Hispanic blacks (20 percent) and non-Hispanic whites (19 percent).
More than two-thirds (71 percent) of cancers occurring in children and adolescents are rare cancers compared with less than 20 percent of cancers diagnosed in patients aged 65 years and older.
Among solid tumors, 59 percent of rare cancers are diagnosed at regional or distant stages compared with 45 percent of common cancers.
In part because of this stage distribution, five-year relative survival is poorer for patients with a rare cancer compared with those diagnosed with a common cancer.
It is the same for males and females.
Fifty-five percent of men diagnosed with a rare cancer will survive five years, compared to 75 percent of men with common cancers.
For women, 60 percent with rare cancers will survive five years, compared to 74 percent with common cancers.
However, 5-year relative survival is substantially higher for children and adolescents diagnosed with a rare cancer (82 percent) than for adults (46 percent for ages 65-79 years).
‘Continued efforts are needed to develop interventions for prevention, early detection, and treatment to reduce the burden of rare cancers, write the authors.
‘Such discoveries can often advance knowledge for all cancers.’