The short answer
Kidney cancer often causes no symptoms early and is frequently found by chance on a scan. When symptoms occur, they can include blood in the urine, a lump or ongoing pain in the side, and unexplained weight loss.
Kidney cancer often causes no symptoms early and is often found by chance on a scan.
Blood in the urine can be a sign.
A lump or ongoing pain in the side or lower back can occur.
Unexplained weight loss and tiredness can also occur.
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The full explanation.
The simple version
The kidneys filter waste from the blood and make urine. Kidney cancer often causes no symptoms early on. Many cases are found by chance, on a scan done for another reason entirely. When symptoms do appear, blood in the urine is one of the more common ones.
Possible signs
Symptoms, when they occur, can include:
- Blood in the urine, which may look pink, red, or brown
- A lump or ongoing pain in the side or lower back
- Unexplained weight loss
- Tiredness that does not improve with rest
- Loss of appetite
- Fever that is not explained by an infection
- Low red blood cell counts found on a routine blood test
No single symptom points clearly to kidney cancer. Each one has other, much more common explanations. That is exactly why a persistent or unexplained version of any of these deserves a doctor's attention.
Many kidney cancers are found by chance on a scan before causing any symptoms.
Why it is often found by accident
Kidney cancer often grows for a long time without causing any noticeable symptoms. The kidneys sit deep in the back of the abdomen, out of easy reach. Many cases are found incidentally. This means a scan done for an unrelated reason, such as a car accident or belly pain from something else, happens to spot a kidney mass. When found this way, kidney cancer is often smaller. It is easier to treat, since it has not yet caused symptoms tied to size or spread.
When symptoms do appear
Blood in the urine, a side or back lump, and pain used to be the classic combination doctors looked for. Today, that full combination is uncommon. It usually signals more advanced disease. Imaging now catches most cases earlier, before all three symptoms have time to develop together.
When to see a doctor
See a doctor for blood in the urine, an ongoing lump or pain in the side, or unexplained weight loss lasting more than a few weeks. These symptoms have many other, more common causes. But they should always be evaluated rather than assumed to be minor.
What tests to expect
Your doctor will likely start with a urine test and blood work. If kidney cancer is suspected, imaging such as an ultrasound or CT scan comes next. These scans can usually tell whether a kidney mass looks concerning. A biopsy or surgery may still be needed to confirm the diagnosis.
What to ask your team
Ask whether your symptoms need imaging. Ask whether a mass found on a scan looks concerning. Ask what tests come next if kidney cancer is suspected. Ask what symptoms should bring you back sooner.
Living with anemia or unexplained fatigue
Some kidney cancers cause low red blood cell counts, called anemia, even without any bleeding you can see. This happens because the kidneys normally help control red blood cell production, and a tumor can interfere with that process. If routine blood work shows anemia with no clear cause, your doctor may consider kidney imaging as part of the workup, especially alongside any other symptoms on this list.
Sources
Words to know
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Common questions
Does kidney cancer cause early symptoms?
Often not. Many kidney cancers are found by chance on an imaging scan done for another reason, before they cause symptoms.
What symptoms can occur?
Possible signs include blood in the urine, a lump or ongoing pain in the side or lower back, unexplained weight loss, tiredness, and sometimes fever.
Do these symptoms mean cancer?
Usually not. Blood in the urine and back pain have many non-cancer causes. But because they can signal kidney cancer, they should be checked.
When should I see a doctor?
See a doctor for blood in the urine, an ongoing lump or pain in the side, or unexplained weight loss.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
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Last updated: 2026-08-05Next planned review: 2027-07-07
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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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