The short answer
Carcinoma in situ (CIS), also called stage 0, means abnormal cells are present but have not spread to nearby tissue. The National Cancer Institute says CIS is not cancer, but it may become cancer. Your care team can explain what your result means for you.
Carcinoma in situ means abnormal cells are present but have not spread to nearby tissue.
It is also called stage 0.
The National Cancer Institute says CIS is not cancer, but it may become cancer.
Your care team can explain what your specific result means and what comes next.
On this page
Choose how you want to read this
The whole article, with every detail and caution.
The short version
This page is for anyone who has seen "carcinoma in situ" (CIS) on a pathology report. That is the report on tissue checked under a microscope. The National Cancer Institute (NCI) describes it as stage 0: abnormal cells are present but have not spread to nearby tissue. NCI adds that CIS is not cancer, but it may become cancer.
Why "in situ" matters
The key point is spread. In CIS, the abnormal cells have not spread to nearby tissue. That is why the finding is called stage 0, the earliest stage on the scale.
Pre-cancer or early cancer?
Care teams may use different words for CIS, depending on the type and where it is. The wording on your report reflects what the pathologist saw under the microscope. Ask your care team how they describe your result.
What usually happens next
Because CIS may become cancer, your care team will talk with you about next steps. These depend on the type and location. Ask what they recommend and why.
What to ask
Ask what type of carcinoma in situ your report describes. Ask whether they consider it pre-cancer or early cancer in your case. Ask what your options are and how closely it needs to be followed. Their reading of your full report is what applies to you.
Sources
Common questions
Is carcinoma in situ cancer?
The National Cancer Institute says carcinoma in situ is not cancer, but it may become cancer. The abnormal cells have not spread to nearby tissue. Words on reports vary, so ask your care team how they describe your result.
Can carcinoma in situ spread?
The National Cancer Institute describes the abnormal cells as not having spread to nearby tissue. Ask your care team what that means for your type and what follow-up they advise.
How is carcinoma in situ treated?
Treatment depends on the type and location. Your care team will explain the options that fit your situation.
Will carcinoma in situ turn into cancer?
It may. The National Cancer Institute says carcinoma in situ may become cancer. Ask your care team how closely to follow your result and what they advise.
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).
More words from this kind of report
Other guides in biopsy & pathology reports.
Your next step
Plain-language definitions for the words on your report.
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.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Sources last checked: 2026-10-02 what this meansLast updated: 2026-10-02Next planned review: 2027-07-14
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 — Editorial review complete. This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team 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.
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: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
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.