Stromal tumor of uncertain malignant potential

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Stromal tumor of uncertain malignant potential (STUMP) is a rare stromal tumor of the prostate with a broad spectrum of histologic pattern and variable clinical behavior.

Terminology

Stromal tumor of uncertain malignant potential has been also known as atypical stromal hyperplasia, cystic epithelial-stromal tumor, cystosarcoma phyllodes or phyllodes variant .

Epidemiology

Stromal tumor of uncertain malignant potential is a rare entity with only a few large case series published. Patients are apparently most commonly affected in their 6 and 7 decade of life .

Clinical presentation

Most common symptoms include urinary frequency and/or urgency, voiding difficulties, poor flow or urinary retention as well as hematuria or hematospermia.  Digital rectal examination (DRE) might reveal prostatic enlargement .

Prostate specific antigen (PSA) might be elevated .

Complications

If left untreated stromal tumor of uncertain malignant might lead to urinary retention.

Pathology

Stromal tumors of uncertain malignant potential are considered prostatic stromal lesions, which cannot be classified as sarcomas and comprise a broad spectrum of histological patterns .

Macroscopic appearance

Macroscopic appearance might vary. Different colors range from white over tan to yellow and consistence might be solid or firm, partially cystic or multiloculated. Cysts may vary considerably in size and content might be serous, mucinous or bloody . Both the transitional and peripheral zone might be involved.

Microscopic appearance

The microscopical appearance will vary, but all of them will feature an expansion of the prostatic stroma. Areas of necrosis are rare and there is usually only very minor mitotic activity .

There are apparently four different patterns of hypercellular stroma associated with :

  • cytological atypia or degenerative atypia 
  • bland fusiform cells looking alike benign prostatic hyperplasia
  • benign glands showing a leaf-like pr phyllodes-like growth
  • bland stromal cells and myxoid pattern
    • Immunohistochemistry

    Immunohistochemistry stains are usually positive for CD34, vimentin and variably with smooth muscle actin. Progesterone receptor will be positive .

    Radiographic features

    Imaging is done to depict the local extent of the tumor and might help in the diagnosis.

    Ultrasound

    Transrectal ultrasound might show multiple hypoechoic, cystic lesions.

    CT

    CT might show a mass with multiple hypodense lesions and enhancing septa after contrast .

    MRI

    MRI might show an expansive well-defined mass with multiple leaf-like cystic changes interspersed by bands or septae or a diffusely heterogenous lesion .

    • T1: homogeneously low signal
    • T2: high signal intensity cystic areas interspersed by low signal intensity bands
    • T1 C (Gd): enhancement of the septae

    Radiology report

    The radiological report should include a description of the following:

    • tumor size and extent
    • localization within the prostate gland
    • signs of extracapsular extension
    • lymph node involvement

    Treatment and prognosis

    Due to a variable and unpredictable behavior of this entity patient management is considered a significant challenge even though many display an indolent course. Therefore a strict follow up is required and surgical management should be considered especially in younger patients .

    History and etymology

    The term stromal tumor of uncertain malignant potential (STUMP) was used after a study by Gaudin in 1998 .

    Differential diagnosis

    Conditions which can mimic the presentation and/or the appearance of a leiomyosarcoma of the prostate gland include: