Uterus

Smooth muscle tumors

Smooth muscle tumors of uncertain malignant potential


Editorial Board Member: C. Blake Gilks, M.D.
Deputy Editor-in-Chief: Jennifer A. Bennett, M.D.
Gulisa Turashvili, M.D., Ph.D.

Topic Completed: 19 August 2021

Minor changes: 30 November 2021

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed search: Smooth muscle tumor of uncertain malignant potential [title]

Gulisa Turashvili, M.D., Ph.D.
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Cite this page: Turashvili G. Smooth muscle tumors of uncertain malignant potential. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/uterusSTUMP.html. Accessed December 3rd, 2021.
Definition / general
  • Smooth muscle tumor with morphologic features exceeding diagnostic criteria for leiomyoma (including subtypes) but insufficient for a diagnosis of leiomyosarcoma
Essential features
  • STUMPs are morphologically heterogeneous and diagnostically challenging, requiring generous sampling for microscopic examination
  • Variable diagnostic criteria proposed for spindle cell, myxoid and epithelioid STUMPs
  • Usually occur in women of reproductive age or postmenopausal women
  • Recurrence rates are 7 - 28%, with higher recurrence rates for epithelioid and myxoid STUMPs
  • Recurrent tumors may look histologically similar to the initial STUMP or may be consistent with leiomyosarcoma
Terminology
  • Spindle cell STUMP
  • Myxoid STUMP
  • Epithelioid STUMP
ICD coding
  • ICD-O: 8897/1 - smooth muscle tumor of uncertain malignant potential
  • ICD-11: 2F76 & XH1EN1 - neoplasms of uncertain behaviour of female genital organs & smooth muscle tumor of uncertain malignant potential
Epidemiology
Sites
  • Myometrium
  • Rarely, broad ligament, ovaries, cervix or vagina
Pathophysiology
Etiology
  • Unknown
Clinical features
Diagnosis
  • Microscopic examination
Radiology description
  • Ultrasonography:
    • Usually circumscribed, showing isoechoic or mixed echogenicity with microcystic anechoic areas, poorly or moderately vascularized with both circumferential and intralesional flows and rarely shadowing (Eur J Obstet Gynecol Reprod Biol 2020;251:167)
  • Magnetic resonance imaging based on limited data:
Prognostic factors
Case reports
Treatment
Gross description
Gross images

Images hosted on other servers:

Intramural tumor with hemorrhage

Frozen section description
  • Not usually diagnosed on frozen section
Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Gulisa Turashvili, M.D., Ph.D.
Coagulative necrosis

Coagulative necrosis

Elevated mitoses

Elevated mitoses

Epithelioid morphology

Epithelioid morphology

Irregular borders

Irregular borders

Virtual slides

Images hosted on other servers:

Epithelioid STUMP

Epithelioid STUMP

Epithelioid STUMP

Positive stains
Negative stains
  • p16: negative or patchy
  • p53: typically wild type
  • CD10: usually negative
Sample pathology report
  • Uterus with cervix, total hysterectomy:
    • Myometrium:
      • Smooth muscle tumor of uncertain malignant potential (see comment)
      • Leiomyomas and adenomyosis
    • Endometrium: proliferative
    • Cervix and uterine serosa: unremarkable
    • Comment: The largest myometrial nodule is well circumscribed and measures 7.5 cm. Microscopically, it is a smooth muscle neoplasm composed of intersecting fascicles of spindle cells lacking cytologic atypia or elevated mitotic activity (3 mitoses seen per 10 HPF, FD = 0.55). However, multiple foci of unequivocal coagulative tumor cell necrosis are present in several blocks. Despite the lack of cytologic atypia or elevated mitoses, the presence of coagulative necrosis warrants classification as a smooth muscle tumor of uncertain malignant potential.
Differential diagnosis
  • Conventional (spindle cell) leiomyoma:
    • Intersecting fascicles of spindle cells, eosinophilic fibrillary cytoplasm and cigar shaped nuclei lacking coagulative necrosis, cytologic atypia or elevated mitotic activity
  • Cellular leiomyoma:
    • More cellular compared with the surrounding myometrium
    • Thick walled vessels and cleft-like spaces
    • Usually spindled cells with scant cytoplasm
    • No coagulative necrosis, cytologic atypia or elevated mitoses
  • Epithelioid leiomyoma:
    • Rounded or polygonal cells with eosinophilic granular or clear cytoplasm with low mitotic count at < 0.8 mitoses / mm2 or < 2 mitoses / 10 HPF (FD = 0.55, 0.24 mm2 in area) and lacking cytologic atypia
  • Myxoid leiomyoma:
    • Circumscribed, hypocellular, myxoid tumor lacking cytologic atypia or mitotic activity
  • Leiomyoma with bizarre nuclei:
    • Cells with bizarre nuclei in a background of typical leiomyoma, lacking coagulative necrosis or elevated mitotic activity (usually < 2 mitoses / mm2 or < 5 mitoses / 10 HPF, FD = 0.55 mm, 0.24 mm2 in area)
  • Fumarate hydratase deficient leiomyoma:
    • Leiomyoma with staghorn vessels, alveolar type edema, scattered cells with bizarre nuclei, enlarged nuclei with prominent nucleoli and perinucleolar haloes, eosinophilic cytoplasmic inclusions
  • Mitotically active leiomyoma:
    • Leiomyoma with elevated mitotic count at 2.5 - 6 mitoses / mm2 or 6 - 14 mitoses / 10 HPF (FD = 0.55 mm, 0.24 mm2 in area) but lacking coagulative necrosis or cytologic atypia
  • Conventional (spindle cell) leiomyosarcoma:
    • 2 of 3 diagnostic features present, including coagulative necrosis, cytologic atypia, elevated mitotic count at ≥ 4 mitoses / mm2 or ≥ 10 mitoses / 10 HPF (FD = 0.55, 0.24 mm2 in area)
  • Epithelioid leiomyosarcoma:
    • Predominant epithelioid morphology (> 50% of overall tumor volume)
    • Moderate to severe cytologic atypia or coagulative necrosis or ≥ 1.6 mitoses / mm2 / ≥ 4 mitoses / 10 HPF (FD = 0.55, 0.24 mm2 in area)
  • Myxoid leiomyosarcoma:
    • Moderate to severe cytologic atypia or coagulative necrosis or > 0.4 mitoses / mm2 / > 1 mitosis / 10 HPF (FD = 0.55, 0.24 mm2 in area) or infiltrative / irregular borders
Board review style question #1
Which of the following smooth muscle tumors falls short for a diagnosis of STUMP?

  1. Smooth muscle tumor lacking coagulative necrosis and cytologic atypia, with 16 mitoses / 10 HPF
  2. Smooth muscle tumor with 3 mitoses / 10 HPF, lacking coagulative necrosis and cytologic atypia
  3. Smooth muscle tumor with coagulative necrosis and 2 mitoses / 10 HPF, lacking cytologic atypia
  4. Smooth muscle tumor with epithelioid morphology and 3 mitoses / 10 HPF, lacking coagulative necrosis and cytologic atypia
  5. Smooth muscle tumor with myxoid morphology, focally irregular borders and mild cytologic atypia, lacking coagulative necrosis or mitotic activity
Board review style answer #1
B. Smooth muscle tumor with 3 mitoses / 10 HPF, lacking coagulative necrosis and cytologic atypia

Comment Here

Reference: Smooth muscle tumors of uncertain malignant potential
Board review style question #2
Which immunohistochemical markers are useful for differentiating leiomyoma from STUMP?

  1. CD10, hormone receptors, p53 and p16
  2. Desmin, h-caldesmon, p53 and p16
  3. Desmin, h-caldesmon, SMA, CD10 and fumarate hydratase
  4. Desmin, h-caldesmon, SMA, CD10 and hormone receptors
  5. Immunohistochemistry has no value in this differential diagnosis
Board review style answer #2
E. Immunohistochemistry has no value in this differential diagnosis

Comment Here

Reference: Smooth muscle tumors of uncertain malignant potential
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