4x 10x SMAS 100

Case history:

This is a biopsy from the olfactory cleft (skull base) in a 71-year-old woman with rhinorrhea. Endoscopically there is a small nodule.

What is the diagnosis?

  1. Reactive stromal spindle cell proliferation
  2. Respiratory epithelial adenomatoid hamartoma
  3. Biphenotypic sinonasal sarcoma
  4. Solitary fibrous tumor

 Answer: C--Biphenotypic sinonasal sarcoma

Sections show a stromal spindle cell proliferation surrounding mildly hyperplastic glands. The cellularity is variable with some fairly cellular areas. Cytologic atypia is modest.  Immunostains are positive for smooth muscle actin, very weakly positive for S-100 and negative for STAT6. A Pax 3 immunostain was performed at an outside institution and was positive.  The findings are that of biphenotypic sinonasal sarcoma. This a recently described low grade sarcoma occurring in the in sinuses. Evidence of smooth muscle differentiation is seen in conjunction with S-100 is the distinguishing feature of the tumor. It is characterized by a spindle cell proliferation that can vary from densely to sparsely cellular but is cytologically fairly bland with modest atypia and mitotic rate.  Staghorn vessels (seen in the SMA stain figure) are seen raising the possibility of a solitary fibrous tumor. Additionally the superficial regions with hyperplastic glands raises the possibility of respiratory epithelial adenomatoid hamartoma. The presence of a Pax 3/ MAML3 fusion is characteristic and staining for Pax3 is helpful for diagnosis.

The current case is on the hypocellular end of the spectrum and the S-100 stain is weak but the presence of Pax3 staining supports the diagnosis.

1. "Sinonasal tumors : News from the WHO with special reference to mesenchymal entities." Agaimy A, Haller F, Hartmann A. Pathologe. 2018 Feb;39(1):18-26. doi: 10.1007/s00292-018-0415-0.

2. "Newly Described Tumor Entities in Sinonasal Tract Pathology." Bishop JA. Head Neck Pathol. 2016 Mar;10(1):23-31. doi: 10.1007/s12105-016-0688-7.                 

3. "Recurrent PAX3-MAML3 fusion in biphenotypic sinonasal sarcoma." Wang X, Bledsoe KL, Graham RP, Asmann YW, Viswanatha DS, Lewis JE, Lewis JT, Chou MM, Yaszemski MJ, Jen J, Westendorf JJ, Oliveira AM. Nat Genet. 2014 Jul;46(7):666-8. doi: 10.1038/ng.2989.

Case contributed by Tom Winokur, M.D., Professor, Anatomic Pathology, UAB Department of Pathology