Breast - nonmalignant
Benign tumors / changes
Benign stromal spindle cell tumors (BSSCT)

Author: Monika Roychowdhury, M.D. (see Authors page)

Revised: 11 September 2015, last major update September 2015

Copyright: (c) 2002-2015,, Inc.

PubMed Search: Benign stromal spindle cell tumors [title]
Definition / General
  • Tumors composed of benign spindle cells, with variable lines of differentiation
  • First described by Toker (Cancer 1981;48:1615)
  • Terminology used in Tavassoli: AFIP: Tumors of the Mammary Gland, Atlas of Tumor Pathology, Series 4, 1st Edition
  • Terminology
  • Myofibroblastoma: BSSCT with predominant myofibroblastic differentiation
  • Spindle cell lipoma: BSSCT with predominant adipocytic component
  • Solitary fibrous tumor / hemangiopericytoma: BSSCT with predominant fibroblastic elements
  • Pathophysiology
  • Represent variations of the same tumor entity, likely arising from the uncommitted vimentin+/CD34+ fibroblasts of the mammary stroma, capable of multidirectional mesenchymal differentiation (Pathol Res Pract 2001;197:453)
  • Can be subtyped into 4 main groups based on morphology and immunohistochemistry:
  • Etiology
  • Mesenchymal tumors composed of cells capable of various lines of differentiation, including fibroblasts, myofibroblasts, adipocytes and smooth muscle cells
  • Histologic variations reflect the features seen in the four types of myofibroblasts:
  • Clinical Features
  • Benign
  • Case Reports
  • Breast spindle cell tumours (Diagn Pathol 2006;1:13)
  • Gross Description
  • Solid, well circumscribed, non cystic breast mass
  • Micro Description
  • Myofibroblastoma:
    • Spindle cells, hyalinized collagen bundles and adipocytes
    • Can have cellular pleomorphism
    • Based on the ratio of components and pleomorphism, subclassified as classic, collagenized, epithelioid, cellular, lipomatous and variants resembling solitary fibrous tumor
  • Spindle cell lipoma: Spindle cells intermingled with adipocytes and collagen bundles
  • Hemangiopericytoma:
    • Closely packed, spindle shaped cells with indistinct cell margins arranged around thin-walled irregular branching vessels
    • The latter may have a 'staghorn' configuration
  • Micro Images
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    Spindle cell carcinoma, CD10, S100, SMA

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    Myofibroblastoma, CD34, S100

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    Spindle cell lipoma, CD34

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    Leiomyosarcoma, desmin

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    Myoepithelial carcinoma, S100, CD10

    Cytology Description
  • Myofibroblastoma: cellular specimen with bipolar spindle cells, bland nuclei with grooves
  • Nonspecific cytologic features for spindle cell lipoma and hemangiopericytoma
  • Positive Stains
  • bcl2, CD10, CD99, smooth muscle actin
  • Spindle cell lipoma: Vimentin, CD34
  • Myofibroblastoma: Vimentin, CD34, Actin, Desmin
  • Hemangiopericytoma: Vimentin, Actin, CD31, CD34, Factor VIII
  • Differential Diagnosis
  • Myoepithelial carcinoma, spindle cell subtype: nuclear atypia, mitotic figures, necrosis, keratin+
  • Myofibrosarcoma: mitotic figures and necrosis
  • Nodular fasciitis: spindle to round plump cells with frequent mitoses, myxoid tissue-culture like stroma, inflammatory lymphocytic component and extravasated RBCs
    • Desmin negative, positive for Actin and focal CD34
  • Sarcomatoid carcinoma: may have hemangiopericytoma-like vascular pattern, but also nuclear atypia, frequent and atypical mitotic figures, necrosis
  • Spindle cell myoepithelioma: no collagen bundles, keratin+