Blog

When people hear the word cancer, they often think about common types such as breast, lung, prostate, or colorectal cancer. However, there are many other cancers that affect a much smaller number of people. These are known as rare cancers.

Rare cancers can develop in almost any part of the body. Some affect specific organs, while others begin in unusual tissues or involve uncommon types of cells. Although each rare cancer affects relatively few people, rare cancers as a group represent a significant share of cancer cases. 

What Are Rare Cancers?

A rare cancer is a cancer that occurs much less frequently than common cancers.

There are many different types of rare cancers. Some may develop in the:

• Brain or spinal cord

• Endocrine system

• Digestive system

• Bones and soft tissues

• Blood or lymphatic system

• Reproductive organs

• Head and neck

Skin

There are also rare subtypes of cancers that are otherwise considered common. For example, a specific genetic subtype of a common cancer may be uncommon enough to require specialized diagnosis and treatment.

Why Are Rare Cancers Difficult to Diagnose?

Getting a cancer diagnosis can involve several steps, but rare cancers can make the process more complicated.

Symptoms May Look Like Other Conditions

Many rare cancers do not initially cause symptoms that clearly point to cancer.

For example, a person may experience tiredness, stomach discomfort, headaches, swelling, weight changes, or pain. These symptoms can occur with many common conditions.

Doctors may first investigate more common explanations before considering a rare cancer. This can sometimes delay diagnosis. Cancer Australia notes that symptoms of rare and less common cancers may be mistaken for more common conditions, which can make diagnosis take longer.

Some Rare Cancers Have Few Recognizable Symptoms

Some rare cancers may not produce noticeable symptoms until they become larger or affect nearby organs.

Others may cause symptoms that depend heavily on where the tumor develops.

For example, a tumor affecting the brain may cause headaches, balance problems, vision changes, seizures, or other neurological symptoms. A tumor in another part of the body may produce completely different symptoms.

This wide variation can make rare cancers difficult to recognize based on symptoms alone.

Age May Sometimes Make Diagnosis More Difficult

Doctors consider a person's age when evaluating symptoms and possible diseases.

Because certain cancers are more common in older adults, cancer may initially seem less likely in a younger person with unusual symptoms. However, rare cancers can affect people of different ages, including children and young adults.

This does not mean that every unusual symptom in a younger person is cancer. Most symptoms have other causes. But persistent or unexplained problems should still be evaluated appropriately.

Limited Experience Can Be a Challenge

Because rare cancers are uncommon, many doctors may see only a small number of cases during their careers.

This can make it harder to recognize a particular rare cancer quickly. The NCI notes that patients with rare cancers may have difficulty finding doctors with extensive experience treating their specific cancer.

In some situations, a patient may need to see a specialist or cancer center with experience in that particular type of disease.

Why Are Tests Important?

There is no single test that can diagnose every cancer.

Doctors may begin with a physical examination and medical history. Depending on the symptoms, they may order blood or urine tests, imaging scans, or other procedures.

Imaging tests such as CT scans, MRI scans, ultrasound, or PET scans can help doctors identify unusual areas in the body.

However, imaging alone may not always tell doctors exactly what type of tumor is present.

Why Is a Biopsy Often Needed?

A biopsy involves removing a sample of tissue so it can be examined under a microscope.

The biopsy can help doctors determine whether abnormal cells are cancerous and identify the type of cancer.

The NCI explains that while several tests may help diagnose cancer, a biopsy is often the only way to confirm that cancer is present.

For rare cancers, the tissue may also need additional laboratory testing to identify specific characteristics of the tumor.

What Role Does Genetic Testing Play?

Cancer cells can contain genetic changes that help doctors understand what type of cancer is present.

Molecular or genomic testing may identify specific changes in a tumor. These results can sometimes help doctors classify the cancer more accurately and determine whether certain targeted treatments may be appropriate.

This can be especially useful when a tumor has unusual characteristics that make its origin or type difficult to determine.

Why Can a Second Opinion Help?

Because rare cancers can be complicated, a second opinion from a specialist may sometimes provide additional information.

A specialist may have more experience with a particular rare tumor and may review:

• Imaging results

• Biopsy samples

• Pathology reports

• Genetic or molecular test results

• Medical history

FAQs

What is considered a rare cancer?

The NCI defines a rare cancer as one that occurs in fewer than 15 people per 100,000 each year.

Why are rare cancers harder to diagnose?

Their symptoms may resemble common health conditions, and healthcare professionals may have limited experience with a specific rare cancer. Patients may also need specialized testing or expert pathology review.

Can a blood test detect rare cancer?

Blood tests can provide useful information, but they usually cannot confirm every type of cancer by themselves. Doctors often combine laboratory tests with imaging and, when appropriate, a biopsy.

Is a biopsy necessary to diagnose cancer?

A biopsy is often the most reliable way to confirm cancer and determine what type of cancer is present, although the exact diagnostic process varies by cancer type.

Conclusion

Rare cancers are cancers that occur less frequently than common types, but they can affect many different parts of the body. Their symptoms can vary widely, and some may resemble common illnesses. This is one reason they can sometimes be difficult to recognize and diagnose.