Ovary and fallopian tube -

Serous tubal intraepithelial carcinoma (STIC)

This article was last reviewed and updated on March 27, 2019
by Emily Goebel, MD FRCPC

Quick facts:

  • Serous tubal intraepithelial carcinoma (STIC) is a non-invasive cancer that starts from the cells that line the inside of the fallopian tube.

  • If left untreated, STIC can turn into an invasive cancer called high grade serous carcinoma.

  • Women with a genetic mutation in the BRCA gene are at higher risk for developing serous tubal intraepithelial carcinoma.

The normal fallopian tube
The fallopian tubes are thin hollow structures that connect the ovaries to the uterus.  During ovulation, the egg is released from the ovary and it travels to the uterus through the fallopian tube. The inside of the fallopian tube is lined by a single layer of cells called ciliated epithelium. Below the epithelium is a layer of muscle. The outer surface of the fallopian tube is made up of a thin layer of loose connective tissue called serosa.

What is serous tubal intraepithelial carcinoma (STIC)?

Serous tubal intraepithelial carcinoma (STIC) is a non-invasive cancer (malignant tumor) that develops from the cells in the epithelium of the fallopian tube.  The tumour is considered non-invasive if the cancer cells are only seen in the epithelium. However, serous tubal intraepithelial carcinoma is a pre-cancerous disease that can, over time, turn into an invasive cancer called high grade serous carcinoma.

 

The diagnosis changes from STIC to high grade serous carcinoma when cancer cells move from the epithelium into the muscular layer or the serosa. The movement of cancer cells into the muscle or serosa is called invasion. The cells of STIC are abnormal and look identical to the cancer cells in serous carcinoma; however, they are only seen in the epithelium.

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.

 

Your pathologist will examine the fallopian tubes under the microscope to look for STIC. 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.

Immunohistochemistry

Your pathologist may perform a test called immunohistochemistry  on your tissue sample to confirm the diagnosis. STIC stains abnormally for a protein called p53. In STIC, p53 will be either strongly positive or completely negative (null).  

 

Ki-67 (also known as MIB-1) 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, which in STIC is usually greater than 40%. 

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