Different parts of the body do not have an equal risk of developing cancers. Some organs and tissues are more susceptible to cancer than others.

Cancer rates can also vary within an organ. For instance, one type of pancreatic cancer may be common, while another type is rare.

According to the National Cancer Institute, rare cancers are those that affect fewer than 40,000 people in the United States each year. They account for 27% of all cancers and 25% of cancer deaths.

This article discusses why some cancers are rarer than others and provides an overview of 10 rare cancers.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Esophageal cancer affects the tube that transports food and beverages from the throat to the stomach. The American Cancer Society (ACS) estimates that in 2021, there will be around 19,260 new cases of esophageal cancer in the U.S. — 15,310 in males and 3,950 in females.

This form of cancer makes up 1% of cancer diagnoses in the U.S. However, it is more common in other parts of the world, including India, southern Africa, northern China, and Iran.

Symptoms may include:

Treatment for esophageal cancer may include:

The 5-year survival rate ranges from 47% for a localized tumor to 5% for metastasized cancer.

Chronic myeloid leukemia (CML) causes the bone marrow to make abnormally high numbers of blood cells. The ACS estimates that doctors will diagnose around 9,110 new cases of CML in the U.S. in 2021 — 5,150 in males and 3,960 in females.

People who have CML may not have symptoms at the time of diagnosis, or they may experience:

The only curative treatment is a bone marrow transplant, but prognosis improves with the targeted therapy drug imatinib mesylate (Gleevec).

No accurate information is available on the outlook for people with CML, but one study found that 90% of people with this treatment were alive after 5 years.

Childhood acute lymphoblastic leukemia (ALL) is one of the cancers of the bone marrow and blood. While it is rare, it is the most common cancer that affects children.

Symptoms of ALL may include:

Treatment for ALL may involve:

  • combination chemotherapy with two or more chemotherapy drugs
  • targeted therapy
  • a stem cell transplant, a bone marrow transplant that replaces unhealthy cells with healthy ones

The 5-year survival rate for children with ALL is around 90%.

Anal cancer occurs in the anus, the opening at the end of the rectum. It is rarer than cancers of the colon or rectum. The ACS estimates that in 2021, around 9,090 new cases of anal cancer will occur in the U.S. — 6,070 in females and 3,020 in males.

Symptoms may include:

Treatment depends on the stage and location of the tumor but may involve:

  • surgery
  • chemotherapy
  • radiation therapy

The 5-year survival rate ranges from 82% for localized tumors to 34% for metastasized tumors.

Merkel cell carcinoma is a rare and aggressive form of skin cancer. It is also known as neuroendocrine carcinoma of the skin or trabecular cancer. According to the Skin Cancer Foundation, there are around 3,000 new cases of Merkel cell carcinoma in the U.S. each year.

The main symptom of Merkel cell carcinoma is a lump developing on skin that receives a lot of sun exposure. The lump will typically be:

  • painless
  • quick to grow
  • firm to touch
  • dome-shaped or raised
  • flushed or darker in color to surrounding skin

Standard treatment options include:

  • surgical removal
  • chemotherapy
  • radiation therapy
  • immunotherapy

According to the ACS, the average 5-year relative survival rate across all stages of Merkel cell carcinoma is 63%.

Thymic carcinoma is a form of cancer that can occur in the outer cells of the thymus, a small organ in the upper chest that creates white blood cells. Thymic carcinoma cells grow quickly and are prone to spreading to other parts of the body, such as the lungs.

In general, cancers affecting the thymus are relatively rare, with approximately 400 new cases occurring in the U.S. each year.

Many people have not experienced symptoms when they receive a diagnosis of thymic carcinoma. However, this cancer can sometimes cause:

Treatment for thymic carcinoma may involve a combination of the following:

  • surgery to remove the cancer
  • chemotherapy
  • radiotherapy
  • hormone therapy
  • targeted therapy

According to the National Cancer Institute, the 5-year mortality rate for inoperable, locally advanced carcinoma is 36%. For carcinoma that has spread to other parts of the body, the rate is 24%.

A hepatoblastoma is a liver cancer that typically happens in the first 3 years of life. According to the American Childhood Cancer Organization, there are 50–70 new cases in the U.S. each year.

Symptoms vary among children, but may include:

Treatment may involve:

A 2019 population-based study suggested that the average 5-year survival rate for children was 81.5%.

A glioblastoma is a type of brain tumor that is usually very aggressive. Although it is the most common malignant primary brain tumor, research states that it has a global prevalence of 0.59 to 5 cases per 100,000 people each year.

Symptoms depend on the location of the tumor but may include:

While this cancer has no cure, treatment may involve:

  • surgery
  • radiation therapy
  • chemotherapy
  • a combination of any of the above

Many people live less than 1 year after receiving a diagnosis.

Ewing sarcoma is a form of cancer that typically grows in bone tissue. This cancer commonly affects children and young adults, with approximately 2.93 children per 100,000 in the U.S. receiving a diagnosis each year.

Symptoms of Ewing sarcoma include:

  • pain and swelling near the affected area
  • a lump
  • fever
  • a bone that breaks with no clear cause

Treatment options include:

  • chemotherapy
  • radiation therapy
  • surgery
  • high-dose chemotherapy with stem cell preservation

According to the ACS, the relative 5-year survival rate for all stages of Ewing sarcoma combined is 61%.

Kaposi sarcoma is cancer that occurs in the cells lining lymph or blood vessels. Between 2009 and 2013, there were approximately 0.5 cases of Kaposi sarcoma per 100,000 people each year in the U.S.

The main symptom of Kaposi sarcoma is the development of purple, red, or brown blotches. These lesions can develop in the following areas:

  • the skin, most often on the legs or face
  • other organs of the body
  • mucous membranes in the mouth, nose, and throat
  • lymph nodes

Treatment options include:

  • radiation therapy
  • highly active antiretroviral therapy
  • surgery
  • cryosurgery
  • chemotherapy
  • immunotherapy

The 5-year relative survival rate for Kaposi sarcoma is 73%.

The body comprises trillions of cells that normally grow and multiply. When cells become abnormal or get old, they die, and new cells take their place.

Sometimes this process does not work as it should, and the abnormal cells multiply instead of dying. These cells form masses, or tumors, which can be benign, meaning noncancerous, or malignant, meaning cancerous. If they are cancerous, they may grow and spread into nearby tissues and can travel to a distant body of the body, also known as metastasis.

Once cancer grows large enough, it can impact normal body functioning. This gives rise to symptoms.

Cancer is the second-highest cause of death in the U.S. More than 600,000 individuals die from it every year in the country. It is worth noting, however, that cancer deaths declined by 27% from 1999–2019.

The rareness of cancers is a complicated subject, and there is currently no universal definition for what a rare cancer is.

A specific type of cancer may be rare because it tends to appear in certain demographic groups more than others. Some cancers may appear rare because they are harder to diagnose correctly. How often certain cancers occur can also differ greatly by geographical location.

One 2015 review suggests that cancer occurs in certain body tissues more often than in others. Some differences stem from inherited genes, while others are due to environmental agents, such as smoking or alcohol use. Yet, these factors do not fully account for the variation in rates among cancers.

The study authors theorize that the major factor that controls the likelihood of a certain tissue developing cancer is the lifetime number of stem cell divisions within it.

According to the concept underlying this theory, changes in genes happen by chance during stem cell divisions called DNA replications. These genetic changes predict a strong correlation between the lifetime number of stem cell divisions and the lifetime risk of cancer in a particular tissue. Upon researching the theory, the authors found the correlation was striking.

Research into rare cancers tends to get less financial and scientific support than more prevalent cancers, which is one reason there is so much uncertainty around them.

Just as common cancers can occur in many body parts, so can rare ones. They can also affect children as well as adults.

Symptoms of rare cancers can vary greatly, depending on what organs and tissues they affect. Treatment often includes surgery, chemotherapy, and radiation but may sometimes involve additional therapies or symptom management.

The outlooks for people with rare forms of cancer also differ, but early detection can make a considerable difference in the survival rates of some cancers.