What is Stromal Hyperplasia?

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  • Written By: Andy Josiah
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 10 March 2020
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Stromal hyperplasia, better known as pseudoangiomatous stromal hyperplasia (PASH), is a type of benign tumor arising from the supporting tissue of cells and usually occurring in the breast. It was first discovered in 1986 when a team of three medical researchers noted nine cases of breast lesions. There have been very few cases of stromal hyperplasia since then, which has led to a lack of significant study on the condition.

Typically, PASH develops from the body's myofibroblasts cells. These are cells that function as a hybrid between the muscle cells known as fibroblasts and non- or smooth muscle cells. The texture of stromal hyperplasia can be described as rubbery and solid, consisting of fibrous and glandular tissue. Also, it provides no pain and is unilateral, meaning that it occurs in one of paired body parts. There are a few cases, however, in which the protrusion has appeared in both structures.

Such a description makes PASH similar to fibroadenomas, which are benign tumors that commonly appear in the breast. The differentiating factor of stromal hyperplasia is its lack of malignancy. It was the ability to tell whether the lesions were angiosarcoma or not that enabled researchers to set stromal hyperplasia apart as a distinctive condition. Angiosarcoma refers to a collection of tumors characterized by uncontrolled growth and danger to health, consequently denoting cancer. Although it can grow, stromal hyperplasia is not cancerous.


The similarities of PASH and fibroadenomas sometimes makes it difficult to diagnose either condition, particularly the former. The condition is usually diagnosed upon a second or third visit to the medical center. Ultrasonography, mammography and magnetic resonance imaging (MRI) are the techniques used to diagnose stromal hyperplasia.

Physicians recommend surgery for patients with large PASH tumors. In some instances, the surgeon would proceed with an operation even if the diagnosis does not confirm such a diagnosis, as a precautionary measure against cancer. In the most extreme cases, mastectomies, which involve the complete removal of a breast, have been performed. A follow-up examination is recommended, as there have been situations in which the lesions recurred.

Since its differentiation in the mid-'80s, stromal hyperplasia has required further study. Even though it is a benign, non-cancerous condition, the medical community has yet to determine its significance. Since there have been very few documented cases of pseudoangiomatous stromal hyperplasia over the years, the possibility of in-depth research of the occurrence has been limited.


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Post 3

If a stromal hyperplasia is not large and if it's not growing, it doesn't have to be removed. I never had mine removed because it's tiny and plus, it can grow back after surgery.

Post 2

@ankara-- I had a breast PASH mass as well and I had it removed it last year. Don't worry about the surgery, you will be fine.

I think PASH is almost always removed because it can look similar to other kinds of tumors and doctors want to remove it as a precautionary measure.

Post 1

I've just been diagnosed with a stromal hyperplasia in my right breast and my doctor wants to remove it.

According to the biopsy results, my PASH is benign, so there is no cancer and the tumor is not very large. Why does it have to be removed?

I actually want them to leave it alone. I'm okay with going back for check-ups frequently to make sure everything is okay. But why should I have surgery for something that's benign? I don't understand this at all.

Does anyone else have PASH in the breast? What treatment is being suggested to you?

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