What Are The Rarest Cancers?

It is estimated that rare cancers make up approximately a quarter of both cancer cases and cancer deaths. In the EU and UK, for example, over 5 million people are affected by rare cancers. Therefore, those qualified as ‘rare’ cancers may not be quite as rare as one would think. Discover everything you may need to know about rare cancers in this GlobMed guide.

What Qualifies A Cancer As Rare?

A cancer may be described as rare if it affects a small number of people, if the cancer starts somewhere unusual in the body, or if the type is unusual and requires a particular treatment. The definition of rare varies amongst experts, from fewer than 2 out of every 100,000  people being diagnosed with that cancer, to fewer than 6 out of every 100,000 (per year). 

Which Cancers Have Been Categorised As Rare?

There are many types of cancer. Cancers can be categorised as common (for example breast cancer, bowel cancer, prostate cancer, and lung cancer), less common (such as kidney cancer, brain tumours, pancreatic cancer, melanoma skin cancer, non-Hodgkin lymphoma, and kidney cancer), and rare (see below). Cancer52 reports 55% of UK cancer deaths are rare/less common cancers

As far as we currently know, there are a little under 200 rare cancers, which can be grouped into 12 broad ‘families’:

• Cancer of the Central Nervous System (CNS)
• Digestive cancer
• Cancer of the endocrine
• Female genital cancer
• Haematological cancer
• Head and neck cancer
• Male genital and urogenital cancer
• Neuroendocrine tumours
• Paediatric cancer (because rates of cancer in children are low, they are considered rare)
• Sarcomas
• Skin cancer
• Thoracic cancer

Some of the rarest* cancers include:

• Adrenal cancers (carcinomas): There are less common than benign adrenal tumours (adenomas). While the exact number diagnosed is not known, it is estimated to be around 200 people per year.  

• Anal cancer: The rate of new cases is around 1.9 per 100 000 per year.
• Bone and joint cancer: New cases are estimated to be around 1 per 100 000 per year. 

• Childhood cancers: Most childhood cancers are considered rare. Childhood brain and other nervous system cancers have a rate of 3.2 new cases per 100 000 children per year. Childhood leukaemia is slightly more common, but still only has a new case rate of 4.9 per 100 000.
• Follicular lymphoma. The rate of new cases is around 2.6 per 100 000.

• Chronic myeloid leukaemia: The rate of new cases is 1.9 per 100,000.

• Chronic myelomonocytic leukaemia: This only occurs in about 4 per 1 000 000 (around 1 100 cases a year). 
• Esophageal cancer: The new cases rate is about 4.2 per 100 000.

• Ewing tumours (Ewing sarcomas): Approximately 1% of all childhood cancers are Ewing tumours, amounting to about 200 children and teens being diagnosed per year. 
• Hodgkin lymphoma: New cases amount to 2.6 per 100 000.
• Kaposi sarcoma: This cancer has risen and fallen with the AIDS epidemic and subsequent treatment initiative, peaking at around 47 cases per 100 000 per year in the 1990s. It now occurs at a rate of about 6 cases per 100 000.
• Laryngeal cancer: The new cases amount to around 2.8 per 100 000.
• Lip cancer: The rate of new cases is about 0.5 per 100 000.
• Lymphocytic leukaemia: New cases of acute lymphocytic leukaemia amount to about 1.8 per 100 000 per year.

• Merkel cell carcinoma: Also called neuroendocrine carcinoma of the skin. Occurring in around 0.23 per 100 000 people. Incidence rates have been on the increase with about 2000 new cases per year. 
• Nasopharyngeal cancer: This is a rare cancer, with less than one case for every 100 000 people each year.

• Pancreatic neuroendocrine tumours: These tumours make up less than 2% of all cancers found in the pancreas each year.
• Penile cancer: Diagnosed in fewer than 1 man in 100 000 each year.

• Retinoblastoma: The most common childhood eye cancer but rare overall, with only 200-300 diagnosed each year. 
• Rhabdomyosarcoma: About 400 to 500 new cases occur each year, mostly in children and teens.
• Salivary gland cancer: Estimated 3 cases in every 100 000 people per year.

• Small intestine cancer: The rate of new cases is 2.5 per 100 000.
• Soft tissue cancer: Heart cancer is included in this group, which has an overall new cases rate of 3.4 per 100 000.
• Thymus cancer: Thymic tumours may be the most common tumours in the front part of the chest cavity, but they occur at a rate of only 1.5 cases per 1 000 000. The exact number diagnosed is unknown, but estimated at around 400 cases a year. 
• Tongue cancer: New cases amounted to 3.6 per 100 000 per year. 
• Uveal melanoma: Incidence of approximately one case per 100 000.
• Vulvar cancer: The rate of new cases is about 2.5 per 100,000 women per year.
• Waldenstrom macroglobulinemia: Incidence rate of around 3 cases per 1 000 000 (just over 1000 diagnosed per year).

*It is important to note that rare cancer statistics are difficult to compare. Due to difficulties in research which we'll cover below, diagnosis and treatment statistics can vary greatly over time between age/gender/sex/race and between locations and sources. For example, the mentioned statistic on nasopharyngeal cancer is true for most parts of the world but is almost 15 times higher in some parts of China (and therefore would not be considered rare in that specific area).

What Are The Main Concerns When Dealing With A Rare Cancer?

Rare cancers are under-represented and underfunded. Due to the unusual symptoms and being generally less recognisable, it can take a lot of time, many consultations and referrals, and more tests than a common cancer. The lack of information available can be frustrating, and you will need patience.

Highly specialised care and treatment are often required, and you may have to travel to find assistance. Second or third opinions and consultations with experts, specialists, and others who experience the disease may be needed. 

Within the healthcare system, research is more difficult when dealing with a rare cancer, as finding enough people to assess or conduct trials with can take a long time and many resources (if feasible at all). This leads to less available information, fewer policies and guidelines, and fewer therapies and treatments. 

When it comes to children, paediatric cancers are considered rare and require different approaches to adult rare cancers as the biological, clinical, and organisational needs are different.

Overall, patients with rare cancer have worse outcomes. The average 5-year relative survival rates of patients with common cancers is 65%, compared to only 47% for patients with rare cancers.

How Are Rare Cancers Treated?

As with common cancers, treatment will depend on where it is, the stage (size and spread), the grade (how abnormal the cells appear), and your overall health, amongst other factors. Types of treatments include surgery, chemotherapy, radiotherapy, hormone therapy, targeted cancer drugs, immunotherapy, stem cell or bone marrow transplant, and treatment within clinical trials. Multiple treatments may also be needed. 

Some subtypes of common cancers could also be rare. These could be treated as the general type is treated, or treated completely differently (an example of this is small cell cancer of the cervix compared to other cervical cancers).

Research On Rare Cancers

Research is happening globally to find more information on rare cancers and better ways of diagnosing and treating them. An example of a current area of research is genome changes and the role they play in diseases, including rare cancers.  Ask a health professional about trials and research groups regarding your cancer.