Mitotically active cellular fibroma of the ovary

What is a mitotically active cellular fibroma?

A mitotically active cellular fibroma is a non-cancerous type of ovarian tumour. It develops from the stromal cells normally found inside the ovary. These tumours can range in size from less than 1.0 cm to over 20 cm. Large mitotically active cellular fibromas can cause symptoms such as pain or abdominal pressure. It is called a ‘mitotically active cellular’ fibroma because the number of mitotic figures (dividing tumour cells) and the density of tumour cells (the number of tumour cells in a given area) are higher compared to the more common ovarian fibroma.

Continue reading to learn more about your pathology report for mitotically active cellular fibroma.

The ovary

The ovaries are part of the female reproductive tract. They are small organs that are attached to the uterus by the fallopian tubes. The outer surface of the ovary is lined by a thin layer of specialized tissue that forms a barrier around the outside of the ovary called the epithelium. The tissue below the epithelium is called the stroma. The stroma cells support the ovary by producing hormones and specialized proteins that hold the tissue together.

How do pathologists make the diagnosis of mitotically active cellular fibroma?

The diagnosis of mitotically active cellular fibroma is usually made after the entire ovary is surgically removed and sent to a pathologist for examination under the microscope. Microscopically, the tumour is made up of long thin cells called spindle cells. The spindle cells are usually arranged in branching groups called fascicles and are surrounded by dense connective tissue that may be described as hyalinized or fibrotic. In contrast to the more common ovarian fibroma, this tumour contains an increased number of mitotic figures (tumour cells dividing to create new tumour cells) and an overall higher density of tumour cells (the number of tumour cells in a given area of tissue). Large tumours or those that have been present for a long time may undergo a series of degenerative changes including hemorrhage (bleeding into the tumour) and infarct-type necrosis (cell death as a result of decreased blood flow).

Your pathologist may perform a test called immunohistochemistry to confirm the diagnosis. When immunohistochemistry is performed, the tumour cells in a mitotically active cellular fibroma are often positive for inhibin, calretinin, WT1, and the hormone receptors estrogen receptor (ER) and progesterone receptor (PR).

by Jason Wasserman MD PhD FRCPC (updated February 9, 2022)
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