Rare Cancers In The U.S.

In every five-cancer diagnoses in the U.S. there is a rare cancer. This is revealed by a report by American Cancer Society appearing in CA:A Cancer Journal for Clinicians, which is a peer-reviewed journal of the American Cancer Society. Rare cancers account for more than two in three cancers occurring in children and adolescents. They believe that the proportion of rare cancers is likely to grow as the use of molecular markers to classify cancers increase.

This presents a unique challenge for clinicians and their patients as the research to identify causes or to develop ways for prevention or early detection is limited or essentially nonexistent. These rare cancers can be challenging to diagnose and often result in numerous physician visits, misdiagnoses and substantial delays in diagnosis.

The treatment options for these cancers are more limited and often less effective than for the normal and more common cancers. There is less preclinical research and fewer clinical trials for the rare cancers that are limited to select high-volume cancer centers. This has become priority for some researchers and public health advocates.

The U.S. has limited published data on the burden of rare cancers.  Carol E. DeSantis, MPH, along with investigators used data from the North American Association of Central Cancer Registries and the Surveillance, Epidemiology and End Results (SEER) program to examine incidence rates, stage at diagnosis and survival for more than 100 rare cancers. These are defined as an incidence of fewer than 6 cases per 100,000 individuals per year in the U.S.

About 20% of those with cancer in the U.S. are diagnosed with a rare cancer, making up a proportion of 24% being Hispanic, 22% of Asian/Pacific Islander patients compared with non-Hispanic blacks of 20%, and non-Hispanic white of 19%. Around 71% or 2/3rds of cancers occurring in children and adolescents are rare cancers compared with less than 20% in patients aged 65 and older.

Around 59% of rare cancers are diagnosed at regional or distant stages compared with 45% of common cancers among solid tumors. This is partly due to the 5-year relative survival that is poorer for patients with a rare cancer compared with those diagnosed with a common cancer among males (55% vs 75%) and females (60% vs 74%). In children and adolescents with a rare cancer (82%) the 5-year relative survival is substantially higher than for adults (46% for ages 65-79).

Interventions for prevention, early detection and treatment to reduce the burden of these cancers require continued efforts. These efforts can also advance knowledge for all cancers, not just for the rare ones.

Dr Fredda Branyon