A cancer is considered rare when fewer than two cases in 100,000 occur in a year, when it occurs in an unusual part of the body, or when it is of an unusual cell type.
Some experts say that one in five people diagnosed with cancer suffers from a rare type of cancer, and that one out of three of these rare cancers is categorized as particularly rare. This includes some 200 different cancer types. Each type is considered rare but when combined, they represent 22 percent of all cancers and therefore fall into a category of their own.
As researchers learn more about cancer, some common types are divided into rare subtypes. For example, small cell cancer of the cervix is a rare subtype of cervical cancer. Similarly, all cancers in children and teenagers are considered rare cancers.
According to the Genetic and Rare Diseases Information Center (GARD), a rare disease is one that occurs in fewer than 200,000 people. This includes both cancer and non-cancer diseases.
The FDA created a list of rare diseases because drug companies were not investing in treatments for them. The Orphan Drug Act of 1983 (USA) created financial incentives to encourage drug manufacturers to research and develop drugs to find viable treatments for these diseases.
Other countries have different definitions for rare diseases. The European Union (EU), for instance, defines a rare disease as one affecting fewer than one in 2,000 people. The Surveillance of Rare Cancers in Europe (RARECARE) considers the frequency with which various cancers appear, or how many cases are newly diagnosed every year. According to this definition, rare cancers are those affecting less than 6 in 100,000 people per year.
Rare cancer survivors have to contend with a number of challenges, such as:
- Five-year survival rates in adults are worse for rare cancers (47%) than for common cancers (65%).
- Late or incorrect diagnosis.
- Lack of access to appropriate therapies and clinical expertise.
- Very limited number of clinical studies due to the small number of patients.
- Lack of interest in developing new therapies due to limitations in the market.
- Few available registries and tissue banks.
The prevalence of cancer research in common cancers such as lung, breast, colon, or prostate creates a gap of adequate information for rare cancers. A recent study found that researchers will likely only make substantial progress in the treatment of these diseases by looking at the molecular subsets of diseases that compose malignant tumours.
Often, information about rare cancers is hard to come by, and survivors might feel isolated in their journey; therefore, it is always good to talk about one’s illness with professionals and family members, as well as finding others with the same disease, perhaps through a support group or an online forum.