The short answer
Seminal vesicle invasion (SVI) means prostate cancer has grown into one or both seminal vesicles, two small glands. After surgery, NCI's staging table lists it as pT3b. This page explains what that means and what to ask your care team.
Seminal vesicle invasion means the cancer has grown into the seminal vesicles, small glands that make semen.
After surgery, NCI's staging table lists it as pT3b.
It describes the main tumor. Ask your care team about lymph nodes and other tests.
Your care team uses it with margins, grade, and PSA to plan follow-up.
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This page is for anyone whose prostate pathology or MRI report mentions seminal vesicle invasion, sometimes shortened to SVI. It explains the term, how it is staged, and what to ask your care team.
What the seminal vesicles are
NCI describes the seminal vesicles as glands that make semen. Seminal vesicle invasion means the cancer has grown into one or both of these glands.
How it is staged
After surgery, the pathologist assigns a pathologic T category (pT). NCI's staging table lists:
- pT2: the cancer is confined to the prostate.
- pT3a: extraprostatic extension, or microscopic spread into the bladder neck.
- pT3b: the tumor grows into the seminal vesicle or vesicles.
- pT4: the tumor is fixed or grows into nearby structures other than the seminal vesicles.
So SVI is pT3b.
What it does and does not tell you
SVI describes how far the main tumor has grown. Ask your care team whether lymph nodes or other organs were checked, and what they showed.
NCI says tools used after surgery to predict outcomes add findings such as capsular invasion, surgical margins, seminal vesicle invasion and lymph node involvement. Those tools describe groups of people. They cannot tell you what will happen to you.
What follow-up involves
Ask your care team what follow-up they plan after surgery, and whether any further treatment makes sense for you. If you are unsure of your plan, ask for it in writing.
Ask these before you leave
- Is SVI on one side or both?
- What is my pathologic T category and full stage?
- Were lymph nodes removed, and what did they show?
- Are my margins negative or positive?
- What follow-up do you plan, and is further treatment recommended?
Related pages
See What Does Extraprostatic Extension Mean?, What Does a Rising PSA Mean?, Prostate Cancer Stages and Grade, and Understanding Your Pathology Report.
Sources
Common questions
What are the seminal vesicles?
NCI describes them as glands that make semen.
What stage is seminal vesicle invasion?
After surgery, NCI lists it as pT3b. The full stage also depends on lymph nodes, grade group, and PSA.
Does SVI mean the cancer has spread to other organs?
Not by itself. It describes how far the main tumor has grown. Ask your care team whether lymph nodes or other tests matter for you.
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Sources last checked: 2026-10-02 what this meansLast updated: 2026-10-02Next planned review: 2027-09-27
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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.
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