Mitotically active cellular fibroma of the ovary

By Jason Wasserman MD PhD FRCPC
June 7, 2023

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.  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.

What are the symptoms of a mitotically active cellular fibroma?

Small tumours typically do not cause any symptoms are may be discovered incidentally when imaging of the pelvis is performed for other reasons. Large mitotically active cellular fibromas can cause symptoms such as pain or abdominal pressure.

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.

What does a mitotically active cellular fibroma look like when viewed 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).