The short answer
Rare cancers together make up just over a quarter of all cancers, but each one is uncommon. NCI says that can mean a longer wait for diagnosis, trouble finding experts, and fewer trials.
NCI defines a rare cancer as one affecting fewer than 40,000 people a year in the US.
Rare cancers together make up just over a quarter of all cancers and about a quarter of cancer deaths.
NCI says people with rare cancers can wait longer for a diagnosis and may struggle to find experts.
Fewer patients means fewer trials and less research material, which makes new treatments harder to develop.
On this page
Choose how you want to read this
The whole article, with every detail and caution.
What "rare" actually means
The National Cancer Institute (NCI) defines rare cancers as those that affect fewer than 40,000 people per year in the US. All childhood cancers are rare by this definition.
Rare cancers together make up just over one quarter of all cancers. They account for about a quarter of cancer deaths each year. The category as a whole is common. Any single rare cancer is not. That mismatch drives much of what follows.
Why the diagnosis can take so long
NCI says people with rare cancers often wait a long time for a definite diagnosis. They may also have trouble finding specialists who know their condition. Some have to travel to get care. Doctors can struggle too. They may lack specialized training in a rare tumor and have trouble finding expert colleagues to consult.
If you are unsure about your diagnosis, ask your care team whether someone with expertise in your tumor type has reviewed the pathology. Asking is not a challenge to the first doctor.
Fewer trials, less certainty
NCI says researchers studying rare cancers have limited tumor samples, no suitable research models, and too few patients for clinical trials of possible treatments. Developing therapies for rare cancers is especially hard for these reasons.
So the useful question is not only "what is the standard treatment." It is also "what is this recommendation based on, and how sure are you?" An honest answer to that is worth having.
The specific loneliness
Support groups often fill with people who have common cancers. It can feel as if nobody around you has heard of your diagnosis. You may spell the name each time you say it. Online searches may turn up little written for patients. This section describes experiences people share. It is not a measured finding from the sources below.
Where to look for connection and information
NCI's MyPART (My Pediatric and Adult Rare Tumor) network includes scientists, patients, family members, advocates and health care providers working on rare tumors. It runs a natural history study. It also holds rare tumor clinics at the NIH Clinical Center, where patients and experts meet to learn more about the tumor from each other. MyPART focuses on young people and children with rare tumors.
NCI also offers LiveHelp at livehelp.cancer.gov and phone support at 1-800-4-CANCER. Ask your care team to name any foundation or patient group for your specific diagnosis. That is a reasonable request.
Sources
Common questions
What counts as a rare cancer?
The National Cancer Institute defines rare cancers as those that affect fewer than 40,000 people per year in the US. All childhood cancers fall in this group because they are uncommon in children.
Why can it be hard to find the right specialist?
NCI says people with rare cancers often wait longer for a definite diagnosis and have trouble finding experts in their condition. Doctors may also struggle to find colleagues with expertise to consult. Some people have to travel to get care.
Why are there fewer trials and treatments?
NCI says researchers face limited tumor samples, a lack of suitable research models, and too few patients for clinical trials of possible therapies.
How do I find anyone else with my diagnosis?
NCI's MyPART network brings together scientists, patients, family members, advocates and health care providers working on rare tumors. Its rare tumor clinics at the NIH Clinical Center let patients and experts learn about the tumor from each other. Ask your care team about other groups for your specific cancer.
Where can I get help finding information?
NCI offers LiveHelp at livehelp.cancer.gov and phone support at 1-800-4-CANCER.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Written by: Cancer ExplainedSources last checked: 2026-07-30 what this meansLast updated: 2026-10-02Next planned review: 2028-07-30
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source checked. This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
General education. Low-risk educational or organizational content. Medical facts are cited to authoritative sources.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.