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8 Rare Cancers You Might Not Know About

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Rare cancers include a wide range of cancer types, from unusual subsets of common cancers to cancers in places they don’t normally appear. Here are 8 different rare cancers you may not know about. 

Though individual rare cancers affect small numbers of patients per year, they collectively make up a sizeable portion of cancer diagnoses. Rare cancers account for an estimated 1 in 4 new cancer diagnoses around the world each year and around 30 percent of all cancer deaths worldwide.1 Unfortunately, these cancers also tend to receive less funding than other more common forms of the disease, resulting in fewer breakthroughs and fewer treatment options for people who need them.    

While different organizations have varying definitions of what makes a cancer rare, the National Cancer Institute defines them as those occurring in fewer than 15 out of every 100,000 people per year in the United States or those diagnosed in fewer than 40,000 people in the U.S. annually.2,3 These can include uncommon subsets of more common cancers, such as triple-negative breast cancer, or cancers in unusual parts of the body, like the appendix. Here are just a few rare cancers that you may not have heard about before.  

1. Sinus cancers 

Sinus cancers, a catch-all term for cancers affecting the nasal cavity and the paranasal sinus area, are a subset of head and neck cancers. These cancers form in the open spaces above and behind the nose and can initially feel like nasal congestion that won’t go away. Sinus cancers more commonly form in the nasal cavity than in the paranasal sinuses (four pairs of hollow spaces within the skull and facial bones around the nose). All combined, around 2,000 people in the U.S. are diagnosed with sinus cancers each year, making up between 3 and 5 percent of head and neck cancer diagnoses and less than 1 percent of general cancer diagnoses each year.4,5 Because there are so many types of cancer that affect the head and neck, sinus cancers can be difficult to initially diagnose.  

2. Bile duct cancer 

Bile duct cancer, or cholangiocarcinoma, affects the tubes that carry bile from the liver to the small intestine. There are two types of bile duct cancer—intrahepatic, which forms in the ducts inside the liver, and extrahepatic, occurring in the ducts outside the liver. Though rare in the United States, with around 8,000 new diagnoses each year, it can be more commonly found in Southeast Asia.6 Because of its rarity and proximity to other major organs, bile duct cancer can be misdiagnosed, leading to uncertainty about the actual prevalence of the disease.7  

3. Adenoid cystic carcinoma 

Adenoid cystic carcinoma (ACC) affects the tissues of various glands within the body. Though it most commonly appears in the salivary glands—making it often a subset of head and neck cancers—it can also form in the lungs, breasts, prostate, or skin. Salivary ACC makes up about 1 percent of head and neck cancer diagnoses every year and is diagnosed in around 4.5 out of 100,000 people per year.8 ACC appears to occur randomly; there aren’t known risk factors, and a family member with ACC does not predict additional ACC diagnoses within that family.9 Because of its rarity and the fact that it often does not cause symptoms, getting a proper diagnosis for ACC can take a while, giving it time to progress within the body before being noticed. 

4. Tonsil cancer 

Tonsil cancer is a subset of throat cancer that affects the tonsils, small lymphatic tissues located at the back of the throat. Most tonsil cancers are squamous cell carcinomas, though they can sometimes be lymphomas (cancers impacting the lymphatic system). Though it isn’t clear what causes tumors to form within the tonsils, tonsil cancer appears to be among the cancers linked to the human papillomavirus (HPV). Though tonsil cancer is the most common type of oropharyngeal cancer (cancer of the middle part of the throat), it’s rare overall, affecting around 8 out of 100,000 people per year in the United States.10 

5. Fallopian tube cancer 

Fallopian tube cancer, which originates in the tubes connecting the ovaries to the uterus, accounts for only 1 to 2 percent of all gynecological cancers and is diagnosed in between 300 and 400 patients annually in the United States. Because of its rarity and the similarity of its symptoms to other cancers or gynecological conditions, fallopian tube cancer can be difficult to diagnose, and researchers still don’t know much about what causes cancer to form there (as opposed to in other parts of the reproductive system), though it’s possible that genetics play a role.11 

6. Appendix cancer 

The appendix, a small organ near the intestines, is still a mystery in and of itself; its exact purpose in the human body remains a subject of debate, and many people have it removed altogether to treat appendicitis. The unusual nature of the appendix, combined with an extremely low occurrence of 1 to 2 diagnoses per million people per year in the United States,12 means that the details of appendix cancer haven’t been well studied. That said, physicians have seen a steady increase in appendix cancer, with rates tripling and even quadrupling among those born in the 1980s compared to those born in the 1940s.13 As a result, researchers are taking more of an interest in solving why appendix cancer occurs and how it can best be treated.  

Meet Dr. John Paul Shen, who researches effective treatment methods for appendix cancer. 

7. Parathyroid cancer 

The parathyroid glands are four glands located behind the thyroid in the neck, and they serve as part of the endocrine system. Cancer of the parathyroid glands can often cause them to become overactive, releasing too much parathyroid hormone at once and leaving the patient at risk for other health conditions like increased calcium in the blood. Parathyroid cancer is extremely rare, with less than 1 diagnosis per 100,000 people per year in the United States and an estimated 3.5 to 5.7 diagnoses per 10 million people per year globally.14-16   

8. Ampullary cancer 

Ampullary cancer affects a part of the digestive tract called the ampulla of Vater, an area of the body where the bile and pancreatic ducts join together and connect to the small intestine. Because of the ampulla of Vater’s critical location in the digestive system, a growing ampullary tumor can affect the functions of the pancreas, small intestine, and liver, leading to a wide array of issues such as bile buildup in the blood, pancreatic inflammation, and gastrointestinal problems like nausea and weight loss. Ampullary cancer diagnoses make up less than 1 percent of gastrointestinal cancer diagnoses, with 4 to 10 diagnoses per million people per year,17,18 though rates are increasing because physicians are developing more accurate ways to detect it.  

References 

1. Global Burden of Rare Cancers: Insights From GLOBOCAN 2022 Estimates https://pmc.ncbi.nlm.nih.gov/articles/PMC12110169/ 

8. Adenoid Cystic Carcinoma: Symptoms, Causes & Treatment https://my.clevelandclinic.org/health/diseases/22212-adenoid-cystic-carcinoma 

13. Birth Cohort Effects in Appendiceal Adenocarcinoma Incidence Across the United States https://www.acpjournals.org/doi/10.7326/ANNALS-24-02479  

14. Parathyroid Cancer: Causes, Symptoms, Diagnosis & Treatment https://my.clevelandclinic.org/health/diseases/6182-parathyroid-cancer 

15. Parathyroid Cancer Treatment (PDQ®) https://www.ncbi.nlm.nih.gov/books/NBK65795/  

16. Parathyroid Carcinoma: Incidence, Survival Analysis, and Management: A Study from the SEER Database and Insights Into Future Therapeutic Perspectives https://pmc.ncbi.nlm.nih.gov/articles/PMC8946517/  

18. Epidemiology, Clinical Presentation, Diagnosis, and Staging of Ampullary Carcinoma https://www.uptodate.com/contents/epidemiology-clinical-presentation-diagnosis-and-staging-of-ampullary-carcinoma