The short answer
Cancer can cause many different signs and symptoms, but most of these symptoms are caused by something other than cancer. Knowing the common warning signs helps you notice changes early and decide when to see a doctor.
Cancer can cause many different signs and symptoms depending on where it is.
Most symptoms that could signal cancer are actually caused by something less serious.
Common warning signs include a lump, unexplained weight loss, fatigue, and unusual bleeding.
A symptom that is new, lasting, or unusual for you is the most important reason to get checked.
Choose how you want to understand this
The full explanation.
The simple version
Cancer can cause many different signs and symptoms, and they depend on where the cancer is and how big it is. The important thing to know is that most of these symptoms are caused by something other than cancer — but because some can be warning signs, it is worth getting new or lasting changes checked.
When to get help sooner
Most warning signs on this page are checked over weeks. A smaller set means today, or right now.
- Call 911 or go to an emergency department if… you have severe difficulty breathing, chest pain that feels tight or heavy, or lips and skin that look blue, grey or pale.
- Call 911 or go to an emergency department if… bleeding is heavy or will not stop — vomiting blood, black tarry stools, toilet water turning red, coughing up more than streaks, or soaking a pad every 1 to 2 hours.
- Call 911 or go to an emergency department if… you have a seizure, a sudden severe headache, sudden confusion, or sudden weakness, numbness or slurred speech.
- Call 911 or go to an emergency department if… a fever comes with confusion, very fast breathing, or a rash that does not fade when pressed.
- Call 911 or go to an emergency department if… new back pain comes with leg weakness, numbness, or loss of bladder or bowel control. Pressure on the spinal cord is treated within hours, and waiting can cost the ability to walk.
Everything else here can be booked. These cannot.
Common warning signs
Signs worth paying attention to include:
- A new lump or swelling anywhere on the body.
- Unexplained weight loss.
- Ongoing tiredness that rest does not fix.
- Unusual bleeding or bruising.
- A sore that does not heal.
- A change in bowel or bladder habits.
- A cough or hoarseness that will not go away.
- A change in a mole or patch of skin.
What to watch for
You do not need to memorize every symptom. The pattern that matters most is a change that is new, that lasts more than a couple of weeks, that keeps getting worse, or that is unusual for you.
A new, lasting, or unusual change is the signal to get checked — not any single symptom.
For specific situations, see the deeper explainers on shortness of breath, bloating, jaundice, loss of appetite, breast pain, blood in urine, rectal bleeding, anemia, vaginal discharge, persistent indigestion, and loss of balance.
When in doubt, ask
Only a doctor can find the cause of a symptom. Getting new or lasting symptoms checked early gives you peace of mind if it is nothing, and the best chance to act early if it is something.
Words to know
Tap any term to see what it means.
Common questions
What are common warning signs of cancer?
Common possible signs include a new lump, unexplained weight loss, ongoing fatigue, unusual bleeding, a sore that does not heal, a change in bowel or bladder habits, a nagging cough, or a change in a mole. Any of these can also be caused by other conditions.
Do these symptoms mean I have cancer?
Usually not. Most of these symptoms are caused by something other than cancer. But because they can be signs of cancer, new or lasting ones should be checked by a doctor.
Which symptoms matter most?
A symptom that is new, lasts more than a couple of weeks, keeps getting worse, or is unusual for you is the most important reason to see a doctor.
Why get symptoms checked early?
Finding cancer early, when it is small and has not spread, often makes it easier to treat. Getting new or lasting symptoms checked promptly gives you the best chance to act if something is wrong.
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).
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Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Last updated: 2026-08-13Next planned review: 2027-07-07
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. We do not employ clinicians and do not intend to — our work 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 checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
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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.
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. We do not employ clinicians and do not intend to — our work 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 checked line by line against the sources listed on it. That confirms the sources support what the page says. 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.
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