by Jason Wasserman MD PhD FRCPC
August 4, 2022
Pseudoangiomatous stromal hyperplasia (PASH) is a non-cancerous growth in the breast. It is made up of specialized cells called myofibroblasts. The growth is called “pseudoangiomatous” (which means “like blood vessels”) because the myofibroblasts form small slit-like spaces that look similar to blood vessels when examined under the microscope.
PASH appears to be caused by hormonal imbalances, in particular the sex hormone progesterone.
Some studies have shown that PASH is associated with a very small increased risk of developing breast cancer over time. However, more studies are necessary and the science remains unclear at this time.
No, PASH is not a precancerous condition and it will not turn into breast cancer over time.
For most patients, PASH does not cause any symptoms and is found incidentally (by accident) when examining breast tissue for another reason. However, for some patients, the area with PASH will become large enough that it can be felt as a lump in the breast. Very rarely, PASH can grow very quickly in one or both breasts mimicking a cancerous tumour. Even when PASH grows quickly, it is not a cancerous tumour.
The diagnosis of PASH is made after tissue from the breast is removed and sent to a pathologist for examination under a microscope. The diagnosis can be made after a surgical procedure called a biopsy is performed to remove a small amount of tissue or after a larger area of tissue is removed in an excision or resection. PASH is often an incidental diagnosis, which means it is found when examining the breast tissue for another reason.