Prostatic stromal tumour of uncertain malignant potential (STUMP)

by Jason Wasserman MD PhD FRCPC
August 14, 2024

Background:

A prostatic stromal tumour of uncertain malignant potential, commonly referred to as STUMP, is a rare type of tumour that arises from the stromal (connective tissue) component of the prostate gland. The term “uncertain malignant potential” is used because it is difficult to predict how the tumour will behave. While most of these tumours remain benign (noncancerous) and do not spread, others may have the potential to grow aggressively or recur after treatment.

What are the symptoms of prostatic stromal tumour of uncertain malignant potential?

The symptoms of a prostatic stromal tumour of uncertain malignant potential can vary depending on the size and location of the tumour. Common symptoms include difficulty urinating, a weak urine stream, and frequent urination, especially at night. Some patients may experience pain in the pelvic area, while others might have no symptoms at all, with the tumour being discovered incidentally during a medical examination or imaging study.

What causes a prostatic stromal tumour of uncertain malignant potential?

The exact cause of prostatic stromal tumours of uncertain malignant potential is not well understood. Like many other types of tumours, prostatic stromal tumour of uncertain malignant potential may arise due to a combination of genetic and environmental factors. However, specific risk factors or genetic mutations associated with the development of this tumour have not yet been identified.

What genetic changes are found in prostatic stromal tumours of uncertain malignant potential?

Currently, there is limited information on the genetic changes associated with prostatic stromal tumours of uncertain malignant potential. Research in this area is ongoing, and further studies are needed to identify specific genetic alterations that may contribute to the development and progression of these tumours.

Microscopic features of this tumour

Under the microscope, a prostatic stromal tumour of uncertain malignant potential can show various patterns of growth. The most common pattern comprises bland-looking spindle cells (long, slender cells) mixed with the normal glands found in the prostate gland. These spindle cells are often arranged in a loose, disorganized pattern. Some tumours show a pattern of growth that mimics the appearance of a phyllodes tumour, a type of tumour more commonly found in the breast. In addition to these patterns, less common variations include myxoid (gel-like) and epithelioid (resembling epithelial cells) patterns.

Immunohistochemistry

Immunohistochemistry (IHC) is a special test that pathologists use to confirm the diagnosis of prostatic stromal tumour of uncertain malignant potential and to rule out other tumours that may look similar under the microscope. This test involves applying specific antibodies to a tissue sample to see if certain proteins are present in the tumour cells. In the case of prostatic stromal tumours of uncertain malignant potential, most tumours are positive for vimentin (a protein found in connective tissue cells) and the progesterone receptor. These tumours are variably positive for CD34, smooth muscle antigen (SMA), and desmin. They uncommonly express the estrogen receptor, a protein typically found in hormone-sensitive tissues.

Prognosis

The prognosis for patients with prostatic stromal tumour of uncertain malignant potential is generally favorable. At present, there are no specific pathologic features that reliably predict more aggressive behaviour in these tumours. However, the majority of patients are cured with surgery alone. This means that once the tumour is surgically removed, it is unlikely to cause further problems. Close follow-up may be recommended to monitor for any signs of recurrence, but the overall outlook for most patients is positive.

Want to learn more about pathology?

Visit the Atlas of Pathology to explore thousands of human pathology images.