by Emily Goebel, MD FRCPC
April 17, 2026
Serous tubal intraepithelial carcinoma — usually called STIC — is a pre-invasive form of cancer that develops in the lining of the fallopian tube. “Intraepithelial” means the abnormal cells are confined to the thin surface layer of the tube and have not grown into the deeper tissue beneath it. Because the cells have not broken through that surface layer, STIC is considered non-invasive. However, STIC is not simply a precancerous condition — the cells already appear and behave as cancerous, and STIC is now understood to be the starting point from which most cases of high-grade serous carcinoma of the ovary develop. This article will help you understand what a STIC diagnosis means, how it is made, and what happens next.
What are the symptoms?
STIC itself does not cause symptoms. It cannot be felt during a physical examination, does not produce a visible mass, and cannot be detected by imaging such as ultrasound or CT scan. For this reason, STIC is rarely diagnosed because of symptoms — it is found in one of two ways: either as an incidental finding when the fallopian tubes are removed during planned surgery (most commonly risk-reducing surgery in someone with a BRCA gene mutation), or when the fallopian tubes are carefully examined as part of a staging operation for high-grade serous carcinoma of the ovary.
What causes STIC?
STIC develops from specialized cells at the fimbrial end of the fallopian tube — the finger-like fringe at the tip of the tube that sits closest to the ovary. These cells are called secretory cells, and they are particularly prone to the DNA damage that leads to STIC. The most important known cause is an inherited mutation in the BRCA1 or BRCA2 genes, which normally help cells repair serious DNA damage. When these genes are not working, DNA errors accumulate over time, and the cells in the fallopian tube lining can become cancerous.
BRCA1 mutations carry a higher risk than BRCA2 mutations. In people who undergo risk-reducing removal of the ovaries and fallopian tubes because of a BRCA mutation, STIC is found in approximately 5–10% of cases — even when no invasive cancer is present. Most cases of STIC outside the setting of BRCA mutation are detected when high-grade serous carcinoma is already present, because the fallopian tube is the site where that cancer originates.
STIC is not associated with Lynch syndrome, endometriosis, or the other risk factors relevant to endometrioid or clear cell carcinoma of the ovary.
Relationship to high-grade serous carcinoma
Understanding STIC requires understanding its relationship to high-grade serous carcinoma — the most common and aggressive type of ovarian cancer. For many years, high-grade serous carcinoma was assumed to originate from the ovarian surface. Research over the past two decades has established that the fallopian tube, not the ovary, is where most of these cancers actually begin. STIC is the precursor lesion — the very earliest stage of disease — before the cancer cells break through the surface of the fallopian tube and spread to the ovary and the lining of the abdomen.
STIC and high-grade serous carcinoma share the same molecular fingerprint, most importantly the near-universal TP53 mutation. When STIC is found alongside an invasive high-grade serous carcinoma, pathologists can often confirm that the two share identical TP53 mutations, which proves that the STIC was the origin of the invasive cancer. In cases where STIC is found on its own — without any invasive cancer — it represents either a very early finding that has not yet progressed, or cancer that has been removed before it had the chance to become invasive.
How is the diagnosis made?
STIC can only be diagnosed by microscopic examination of the fallopian tube by a pathologist. It is invisible to the naked eye and cannot be identified by the surgeon during the operation. For this reason, the way the fallopian tube is processed in the laboratory matters enormously. The standard approach is called the SEE-FIM protocol (Sectioning and Extensively Examining the Fimbriated End), in which the fimbrial end of the tube — where STIC most commonly arises — is carefully cut into thin sections and submitted in its entirety for microscopic examination. Without this thorough sampling approach, STIC may be missed.
Under the microscope, STIC appears as a replacement of the normal fallopian tube lining by large, abnormal-looking cells. Normal secretory cells in the fallopian tube are small and orderly; STIC cells are larger, with dark (hyperchromatic) nuclei that vary in size and shape (a feature called nuclear pleomorphism). The normal surface cells of the tube have tiny hair-like projections called cilia; STIC cells typically lack these. Dividing cells (mitotic figures) are commonly visible.
To confirm the diagnosis, the pathologist uses immunohistochemistry (IHC) — a technique that uses antibodies to detect specific proteins in cells. Two markers are used together. First, p53 staining: the cells in STIC typically show an abnormal p53 pattern — either strong staining in virtually all cells (reflecting a gain-of-function TP53 mutation) or a complete absence of staining (reflecting a loss-of-function mutation). Normal tubal epithelium shows patchy, moderate p53 staining. Second, Ki-67 staining: Ki-67 is a protein that marks cells that are actively dividing. In STIC, Ki-67 staining is elevated, with typically more than 10% of cells positive — often substantially higher. The combination of abnormal p53 and elevated Ki-67 in a cytologically abnormal area of tubal epithelium confirms the diagnosis of STIC.
A related but less severe finding is called a “p53 signature” — an area of tubal epithelium with abnormal p53 staining but normal-looking cells and a low Ki-67 index. A p53 signature is not STIC and is not a cancer diagnosis; it is thought to represent a very early molecular change that has not yet fulfilled the criteria for STIC. If your report mentions a p53 signature, this does not require the same management as a STIC diagnosis.
Histologic grade
STIC is not assigned a histologic grade. Because it is a pre-invasive lesion confined to the surface lining of the fallopian tube, the grading systems used for invasive cancers do not apply. STIC is by its nature a high-grade lesion — it is the precursor to high-grade serous carcinoma, never to low-grade serous carcinoma — and no further grading classification is used.
Biomarker and molecular testing
Routine biomarker testing of the type performed for invasive ovarian cancer — such as BRCA tumor testing, HRD testing, MMR testing, or FOLR1 testing — is not typically performed on a STIC specimen. STIC is a pre-invasive lesion for which the management does not currently depend on these molecular results.
The most clinically important molecular consideration when STIC is diagnosed is germline BRCA testing — testing of a blood or saliva sample to determine whether the patient carries an inherited BRCA1 or BRCA2 mutation. If germline BRCA testing has not already been performed, a STIC diagnosis is a strong indication to arrange it, particularly in patients who did not already know they carried a BRCA mutation. This is because BRCA mutations dramatically increase the lifetime risk of high-grade serous carcinoma, and a positive result has important implications for surveillance and prevention in the patient’s blood relatives.
In cases where STIC is found alongside an invasive high-grade serous carcinoma, the full biomarker workup is performed on the invasive carcinoma component, not the STIC. For information about those tests, see the article on High-Grade Serous Carcinoma of the Ovary.
For more information about BRCA testing, see BRCA1 and BRCA2 in Ovarian Cancer.
What does a STIC diagnosis mean for me?
The meaning of a STIC diagnosis depends significantly on the context in which it was found. There are two main scenarios:
STIC found at-risk-reducing surgery, with no invasive cancer: This is an early and important finding. The cancer cells are confined to the surface of the fallopian tube and have not spread. Because the fallopian tube has been removed — which is the goal of risk-reducing surgery — the STIC has been completely excised. The immediate risk from the STIC itself is eliminated. However, the finding confirms that cancer-prone cells were already present, which reinforces the importance of verifying that the opposite fallopian tube and both ovaries were also removed and have been carefully examined. It also underscores the relevance of germline BRCA testing if it has not already been performed.
STIC found alongside an invasive high-grade serous carcinoma: In this scenario, STIC represents the site of origin of the invasive cancer. Finding STIC confirms that the cancer began in the fallopian tube, which is now understood to be the usual origin of high-grade serous carcinoma. The STIC finding itself does not change the staging or treatment of the invasive cancer — what matters clinically is the extent of the invasive carcinoma.
STIC found incidentally when tubes were removed for another reason (e.g., tubal ligation or benign gynecologic surgery): This is a less common but important scenario. The fallopian tube on the opposite side has not been removed, and the ovaries are still in place. This situation requires careful discussion with a gynecologic oncologist about the risk of future invasive cancer and whether removal of the remaining tube and ovaries is appropriate.
What happens after the diagnosis?
Management after a STIC diagnosis depends on the clinical scenario.
When STIC is found at risk-reducing bilateral salpingo-oophorectomy in a patient with a known BRCA mutation, and no invasive cancer is identified, close follow-up is still required. The pathologist will confirm that all submitted tissue has been examined using the SEE-FIM protocol and that no invasive carcinoma is present. Peritoneal washings taken at surgery are also examined for cancer cells. If everything is negative, no additional treatment is needed, but ongoing surveillance and follow-up with the gynecologic oncologist and genetics team is recommended. The peritoneum — the lining of the abdominal cavity — retains a small residual risk of developing primary peritoneal carcinoma even after removal of the tubes and ovaries, and this risk should be discussed with your care team.
When STIC is found alongside an invasive high-grade serous carcinoma, treatment is directed at the invasive cancer. It follows the standard approach for that diagnosis, including cytoreductive surgery and platinum-based chemotherapy. See the article on High-Grade Serous Carcinoma of the Ovary for full details.
When STIC is found incidentally — in someone who did not have risk-reducing surgery and did not know they were at elevated risk — a referral to a gynecologic oncologist and a genetic counselor is urgently recommended. Germline BRCA testing should be arranged promptly. Depending on the results and the clinical situation, removal of the remaining fallopian tube and ovaries will likely be discussed.
In all cases, a STIC diagnosis is an indication to refer first-degree blood relatives — parents, siblings, and children — to a genetic counselor for consideration of BRCA testing, given the hereditary implications.
Questions to ask your doctor
- Was STIC the only finding, or was an invasive cancer also identified?
- Was my fallopian tube examined using the SEE-FIM protocol, and was the tissue fully sampled?
- Were peritoneal washings taken at surgery, and were cancer cells found in them?
- Has germline BRCA testing been performed? If not, should it be arranged now?
- Was my other fallopian tube and both ovaries also removed and examined, and were they normal?
- If my other tube and ovaries were not removed, what is the recommendation going forward?
- What is my residual risk of peritoneal carcinoma now that my tubes and ovaries have been removed?
- Should my family members be referred for BRCA testing?
- What follow-up schedule do you recommend, and what should I watch for?
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