This was a problematic case that originally led us astray. By H and E
morphology, the tumor has a striking storiform pattern merging with
areas with less cellularity and a myxoid background. The CD34 stain
was strongly positive within the less cellular foci but negative within the
cellular storiform and herringbone foci. Thus based upon these findings,
a diagnosis of dermatofibrosarcoma protuberans with focal fibrosarcomatous
transformation was favored. Typically, in this latter lesion, the fibrosarcomatous
portion is negative for CD34. The increased cellularity as well as focally
increased mitotic rate within this focus supported this intepretation.
However, all was definitely not what it appeared to be! This was a very
large excision, encompassing over 25 slides. On only one section, there
was an area that appeared different with a neural appearance. (See images 1-3).
The pattern was reminiscent of a plexiform neurofibroma.
Image 1-Note the plexiform configuration of the tumor.
Image 2
Image 3
Because of these neural features, an S100 stain was obtained which
demonstrated diffuse and strong positivity throughout the entire
tumor (see image 4).
Image 4
Thus, putting all of the information together, the diagnosis of a
Malignant Peripheral Nerve Sheath Tumor was made. The S100
positivity essentially excludes the prior working diagnosis of DFSP. Because
of the features of a plexiform neurofibroma in one section, we queried the
physician submitting the case as to whether the patient had any evidence for
von Recklinghausen's disease (Neurofibromatosis). However, she was in
otherwise good health with none of the clincal stigmata of the latter disease.
This case is an excellent example of how many tumors have histologic patterns
that mimic others. It also illustrates the pitfalls of relying on the results of a limited
number of immunoperoxidase stains. In this case, the CD34 positivity led us
down an erroneous path.
What do you think about this case? I will post your comments anonymously.
COMMENTS:
I was definitely going to call it DFSP based on the initial sections...Always be wary..
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