Prostate gland & seminal vesicles

Seminal vesicles

Mixed epithelial and stromal tumor


Resident / Fellow Advisory Board: Alcino Pires Gama, M.D.
Deputy Editor-in-Chief: Maria Tretiakova, M.D., Ph.D.
Jiejun Wu, M.D., Ph.D.
Kenneth A. Iczkowski, M.D.

Last author update: 20 February 2024
Last staff update: 20 February 2024

Copyright: 2022-2024, PathologyOutlines.com, Inc.

PubMed Search: Mixed epithelial and stromal tumor

Jiejun Wu, M.D., Ph.D.
Kenneth A. Iczkowski, M.D.
Page views in 2023: 234
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Cite this page: Wu J, Iczkowski KA. Mixed epithelial and stromal tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/prostatemixedepithelialandstromal.html. Accessed May 19th, 2024.
Definition / general
  • Biphasic seminal vesicle tumors with both benign epithelial component (often cystic) and benign to malignant stromal component
Essential features
  • Rare biphasic tumor as defined above
  • 3 tiered system has been proposed, including benign lesion to a low grade or high grade malignancy based on the stromal cellularity, atypia, mitosis and necrosis (Adv Anat Pathol 2015;22:113)
    • WHO Urinary and Male Genital Tumors does not mention this 3 tiered system but still emphasizes evaluating the stroma for possible malignant features
  • Main differential diagnoses include seminal vesicle cystadenoma, mesenchymal tumors of seminal vesicle, prostatic stromal tumor of uncertain malignant potential (STUMP), spread of prostate cancer and prostatic stromal sarcoma; biopsy may not be able to differentiate a cystadenoma from a mixed epithelial and stromal tumor (MEST)
Terminology
  • Alternative terms discouraged by WHO 2022: (cystic) epithelial-stromal tumor, fibroadenoma, adenomyoma, cystomyoma, mesenchymoma, mesonephric hamartoma, Müllerian adenosarcoma-like tumor, phyllodes tumor, cystosarcoma phyllodes
  • Cystadenoma once was included in this category but now is recognized as a separate entity with limited stromal proliferation and stromal hypocellularity (WHO)
ICD coding
  • ICD-O: 8959/0 - benign cystic nephroma
  • ICD-11: 2F34 & XH0533 - benign neoplasm of male genital organs & mixed epithelial and stromal tumor
Epidemiology
Sites
  • Seminal vesicle
Pathophysiology
  • Unknown
Etiology
  • Unknown
Clinical features
  • Obstructive lower urinary tract symptoms, dysuria, hematuria, lower abdominal pain or asymptomatic
Diagnosis
  • Mass above the prostate may be detected by digital rectal examination
  • Computed tomography (CT), magnetic resonance imaging (MRI) or ultrasound; imaging may be the key to determining the origin of the tumor and is especially helpful in biopsy
  • Transrectal biopsy, fine needle aspiration or rarely transurethral seminal vesiculoscopy (Urology 2022:167:13)
    • Biopsy may not be able to differentiate a cystadenoma from a MEST
Radiology description
  • MRI can show tissue planes between the lesion and adjacent structures, allowing a conservative surgical approach and not laparotomy (World J Surg Oncol 2008:6:101)
  • Benign mass is distinct from the prostate, in the middle of the seminal vesicle, surrounded by thin capsule with contrast enhanced irregularities of low and high signal intensity by T1 and T2 weighted imaging, respectively (IJU Case Rep 2020;3:103, Int J Urol 2006;13:640)
  • For rare high grade malignant cases, mass was still distinct from other structures but with some hyperintensity on T1 (Case Rep Urol 2014:2014:302708)
Radiology images

Images hosted on other servers:
Pelvic MRI, seminal vesicle mass

Pelvic MRI, seminal vesicle mass

Prognostic factors
Case reports
Treatment
Gross description
  • Well circumscribed, lobulated, solid and cystic mass in the seminal vesicle; contiguous with seminal vesicle remnants and separable from prostate or bladder
  • Most reported MESTs are unilateral
  • Size range: 2.5 - 65 cm (J Surg Case Rep 2023;2023:rjad490)
Gross images

Contributed by Gladell Paner, M.D.
Mass of seminal vesicle

Mass of seminal vesicle

Microscopic (histologic) description
  • Benign epithelial component
  • Stromal component
    • Determines biologic behavior of the tumor
    • Ranges from benign spindle cells separated by collagenous stroma, overlapping with adenofibroma and adenomyoma, to malignant morphology, including reported malignant adenosarcoma or cystosarcoma phyllodes patterns
    • Tendency of spindle cells to be more cellular or condensed around cysts / glands
    • Benign versus malignant distinction is based on cellularity, atypia, mitosis and necrosis
    • Degenerative atypia or mature adipose tissue may be present (Adv Anat Pathol 2015;22:113, Int J Urol 2002;9:599, Cancer 1993;71:2055, Am J Surg Pathol 1987;11:210)
    • May need immunohistochemical staining for differential diagnosis (Adv Anat Pathol 2015;22:113)
Microscopic (histologic) images

Contributed by Fiona Maclean, M.D. and Gladell Paner, M.D.
Cellular stroma surrounds epithelium

Cellular stroma surrounds epithelium

Urothelial component

Urothelial component

Negative stains
Sample pathology report
  • Seminal vesicle, biopsy:
    • Proliferation of bland spindle cells around benign columnar epithelium consistent with mixed epithelial and stromal tumor (see comment)
    • Comment: This is a rare tumor. There are some cases reported in which the stromal component is malignant; however, in the current case, the stroma exhibits benign histologic features.
Differential diagnosis
Board review style question #1

What is the most likely diagnosis of this seminal vesicle tumor?

  1. Benign mixed epithelial and stromal tumor of seminal vesicle
  2. Leiomyoma
  3. Leiomyosarcoma
  4. Malignant mixed epithelial and stromal tumor of seminal vesicle
  5. Seminal vesicle cystadenoma
Board review style answer #1
A. Benign mixed epithelial and stromal tumor of seminal vesicle. The lesion arises from the seminal vesicle with both bland epithelial and spindle-like proliferation of stromal component, which meets the definition of MEST. The stromal component also has a cellular appearance but without atypia, mitosis and necrosis that raise the concern of malignancy. Therefore, this is most likely a benign MEST.

Answers B and C are incorrect because these 2 entities are pure stromal tumors without epithelial components. In this case, there is an epithelial component that does not strongly resemble smooth muscle and nuclear orientation is too random for leiomyoma. The diagnosis is not leiomyosarcoma because of the epithelial component, plus the stroma lacks any atypia. Answer D is incorrect because the stromal component lacks malignant features such as atypia, mitosis and necrosis. Answer E is incorrect because per the 5th edition of WHO, seminal vesicle cystadenoma lacks stromal component proliferation usually with hypocellular stroma and is currently separated from MEST.

Comment Here

Reference: Mixed epithelial and stromal tumor
Board review style question #2
Which of the following is true for mixed epithelial stromal tumor of seminal vesicle?

  1. Biphasic tumor with benign or malignant epithelial and stromal components
  2. Epithelial component is usually positive for CK7, PAX8 and NKX3.1
  3. It includes seminal vesicle cystadenoma
  4. Majority are benign
  5. Stomal component is usually negative for ER, PR and CD34
Board review style answer #2
D. Majority are benign. Answer A is incorrect because per the 5th edition of WHO, the epithelial component cannot be malignant. Answer B is incorrect because the epithelial component is benign and usually positive for CK7 and PAX8 but negative for prostatic markers such as NKX3.1. Answer E is incorrect because the stromal component is usually positive for ER, PR and CD34. Answer C is incorrect because seminal vesicle cystadenoma lacks a stromal component proliferation and is currently separated from MEST.

Comment Here

Reference: Mixed epithelial and stromal tumor
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