Mammary Type Myofibroblastoma
Definition
- Circumscribed soft tissue tumor composed of spindle cells and frequently fat, CD34 and desmin positive, Rb negative
Note: the following are related in name only
- Mammary Type Myofibroblastoma is a circumscribed soft tissue tumor frequently containing fat, lacking Rb expression
- Intranodal Palisaded Myofibroblastoma is an intranodal tumor with increased beta-catenin expression
- Superficial Myofibroblastoma is a superficial lesion that is that does not involve fat and is restricted to the external female reproductive tract
Diagnostic Features
- Bland spindle cells
- Relatively short, stubby nuclei
- Indistinct cell borders
- Mitotic figures rare
- Adipocytes range from absent to predominant
- Collagenous stroma
- Frequently sheet-like
- Occasionally ropey
- Frequently hyalinized or myxoid
- 90% CD34 and Desmin positive with loss of nuclear Rb
- SMA and EMA 40%
- Occasional cases S100, MDM2 or CDK4 positive
- Rb loss due to deletion or rearrangement of 13q14
- Grossly circumscribed
- Intramuscular tumors may be infiltrative
- Mean size 7 cm
- Occasional findings
- Epithelioid cells
- Scattered foci of large hyperchromatic cells
- Degenerate atypia, no mitoses
- Palisading nuclei
- Mean age 54 years (range 4-96)
- M:F 2:1
- Wide distribution
- Most common in groin, inguinal, also breast, trunk , lower extremity
- May be intra-abdominal
- Uncommon in head/neck and upper extremity
- Does not recur or spread, even if incompletely excised
- May form a spectrum with spindle cell lipoma and cellular angiofibroma
- All have deletion or rearrangement of 13q14 with loss of nuclear Rb
- All are benign
Differential Diagnosis
Usually diffuse collagen |
Ropey collagen |
Wispy collagen with prominent round vessels |
Desmin positive |
Desmin negative |
Desmin variable |
| Mammary Type Myofibroblastoma | |
Desmin positive |
Desmin negative |
Loss of Rb |
Rb positive |
STAT6 negative |
STAT6 positive |
Mammary Type Myofibroblastoma |
|
Indistinct short stubby cells |
Long fascicles of spindle cells |
Desmin positive |
Desmin negative |
Loss of Rb |
Rb positive |
Beta catenin negative |
Beta catenin positive |
Mammary Type Myofibroblastoma |
|
No atypical fat cells |
Lipoblasts |
CD34 and Desmin positive |
CD34 and Desmin negative |
Loss of Rb |
Rb positive |
MDM2, CDK4 negative |
MDM2, CDK4 positive |
Bibliography
- Howitt BE, Fletcher CD. Mammary-type Myofibroblastoma: Clinicopathologic Characterization in a Series of 143 Cases. Am J Surg Pathol. 2016 Mar;40(3):361-7. PubMed PMID: 26523539.
- McMenamin ME, Fletcher CD. Mammary-type myofibroblastoma of soft tissue: a tumor closely related to spindle cell lipoma. Am J Surg Pathol. 2001 Aug;25(8):1022-9. PubMed PMID: 11474286.
- Flucke U, van Krieken JH, Mentzel T. Cellular angiofibroma: analysis of 25 cases emphasizing its relationship to spindle cell lipoma and mammary-type myofibroblastoma. Mod Pathol. 2011 Jan;24(1):82-9. doi: 10.1038/modpathol.2010.170. Epub 2010 Sep 17. PubMed PMID: 20852591.
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting 3/14/16
