Page views in 2023: 13
Page views in 2024 to date: 10
8 April 2015 - Case #348

All cases are archived on our website. To view them sorted by case number, diagnosis or category, visit our main Case of the Month page. To subscribe or unsubscribe to Case of the Month or our other email lists, click here.

Thanks to Dr. Feriyl Bhaijee, University of Mississippi Medical Center (USA), for contributing this case.


Website news:

(1) Thanks to your support, March 2015 had record traffic of 679,473 visits (average of 21,918 visits per day) and a record 2.62 million page views. Phase 2 of our Website upgrade will probably not start until mid May 2015. Read more.

(2) Thanks to all who stopped by our booth at USCAP. We also signed up many new authors and likely members of our Editorial Board.

(3) Our website continues to be a free, no registration website focused on the needs of the pathology community. But we have started an optional Membership feature to support the expensive changes we are undertaking, including expanded IT capabilities (new Home Page, new Chapter and topic templates, better Search, improved Mobile use), expanded Editorial Board and more frequent topic updates.

Thanks to new members:

Leadership level: Pathology Associates of Norwood, Massachusetts

Basic level:
  • Jorge Billoch, M.D., San Juan, Puerto Rico
  • Jerad M. Gardner, M.D., University of Arkansas for Medical Sciences
  • Sara C. Shalin, M.D., Ph.D., University of Arkansas for Medical Sciences
  • David R. Stockman, M.D., M.S., University of South Carolina School of Medicine
  • Debra Zynger, M.D., The Ohio State University
Resident / Fellow level: Abul Ala Syed Rifat Mannan M.D., Mount Sinai - St. Luke's Roosevelt Hospital Center, New York.

Visit and follow our Blog to see recent updates to the website.

Case #348

Clinical history:
A 56 year old man presented with a 5 cm painless mass in his thigh, which was surgically excised. Grossly, the mass was well circumscribed with an osseous rim.

Microscopic images:

What is your diagnosis?

Click here for diagnosis and discussion:

Diagnosis: Ossifying fibromyxoid tumor of soft parts

Immunohistochemistry on the lesional cells showed focal S100, neurofilament and desmin positivity. IHC and molecular studies for INI1 were not performed (unfortunately).

Ossifying fibromyxoid tumor of soft tissue is a rare mesenchymal tumor of intermediate malignancy characterized by peripheral metaplastic bone and cords of bland, round cells in a fibromyxoid matrix. It was first described in 1989 by Enzinger, Weiss and Liang as a tumor of primarily adults with a male predominance, presenting as a small, painless, well circumscribed mass in subcutis or muscle, typically in the extremities, trunk or head and neck region (Am J Surg Pathol 1989;13:817).

Grossly, the tumors have a median size of 3 - 5 cm (range 1 to 21 cm). They classically have lobular architecture, corded and trabecular growth patterns, moderate amounts of myxocollagenous matrix and often focal peripheral metaplastic bone formation (Am J Surg Pathol 2008;32:996). The tumor cells usually have indistinct cytoplasm, vesicular nuclei, no / mild atypia and no / minimal mitotic activity.

Tumors are typically S100+, with occasional focal positivity for desmin, GFAP and AE1 / AE3. INI1 is lost in a mosaic pattern in 74% and FISH shows INI1 deletion in 71% (Am J Surg Pathol 2011;35:1615). Up to 85% demonstrate recurrent gene rearrangements, typically PHF1 (49 - 80%) (Am J Surg Pathol 2013;37:1751, Genes Chromosomes Cancer 2014;53:183). Similar gene fusions have been found in endometrial stromal sarcoma.

Cases have been divided into typical, atypical and malignant, using the Folpe and Weiss system, based on high cellularity, high nuclear grade or > 2 MF/50 HPF (Am J Surg Pathol 2003;27:421). Excision of typical and atypical cases is usually curative. Malignant cases are associated with local recurrence, metastases or death (Am J Surg Pathol 2011;35:1615).

Image 01 Image 02