Serous tubal intraepithelial carcinoma (STIC)

by Emily Goebel, MD FRCPC
May 16, 2023

What is serous tubal intraepithelial carcinoma (STIC)?

Serous tubal intraepithelial carcinoma (STIC) is a non-invasive type of fallopian tube cancer. It develops from the cells that cover the inside surface of the fallopian tube. If left untreated, STIC can turn into an invasive type of cancer called high-grade serous carcinoma.

Why is serous tubular intraepithelial carcinoma called a non-invasive type of cancer?

STIC is called a non-invasive type of cancer because the tumour cells are found only in a thin layer of tissue on the inside of the fallopian tube. This layer of tissue is called the epithelium.

What genetic syndromes are associated with serous tubal intraepithelial carcinoma?

Patients who have had breast cancer and/or genetic testing showing a mutation in the gene BRCA are at risk for STIC and may have their fallopian tubes and ovaries removed prophylactically, meaning that these organs are removed prior to the diagnosis of STIC or carcinoma in order to reduce the risk of disease.

How is the diagnosis of serous tubal intraepithelial carcinoma made?

The diagnosis of STIC can only be made after the entire fallopian tube is examined under the microscope by a pathologist. This diagnosis can be made alone or in women who have also been diagnosed with high-grade serous carcinoma of the ovary. In some cases, the diagnosis is made after the fallopian tube is removed for other reasons such as tubal ligation for family planning.

What does serous tubal intraepithelial carcinoma look like under the microscope?

When examined under the microscope, STIC is made up of large abnormal-looking cells. The nuclei (the part of the cell that holds the genetic material) are hyperchromatic (darker than normal) and pleomorphic (varying in shape and size). Unlike normal epithelial cells in the fallopian tube, the cells in STIC tend to lack small finger-like projections called cilia. Mitotic figures (dividing tumour cells) are also commonly seen.

What other tests may be performed to confirm the diagnosis?

Your pathologist may perform a test called immunohistochemistry on your tissue sample to confirm the diagnosis. The cells often show abnormal expression of a protein called p53. That means that p53 will be either strongly positive or completely negative (null).

Ki-67 is a protein that increases when cells are dividing.  In STIC, Ki-67 is usually increased and your pathologist may describe the percentage of cells that are positive for the protein. This is called the proliferative index and in STIC it is typically greater than 40%.