Abstract: Dermatofibromas (DF) are common, benign, skin tumors, usually easily differentiated from dermatofibrosarcoma protuberans (DFSP) by the presence of a relative low cellularity, lesser degree of infiltration of subcutaneous tissue, and immunohistochemical pattern (eg, FXIIIa in DF and CD34 in DFSP). Atypical fibrohistiocytic lesions (AFL) have features intermediate to DF and DFSP (trunk location, storiform pattern, infiltration of the subcutaneous tissue, and focal expression of both CD34 and Factor XIIIa). It is unclear if mitotic counts/degree of proliferation is helpful to distinguish DF from DFSP. To study the mitotic rate and proliferation index in DF, AFL/DFSP, anti-ki67, and anti-PHH3 were performed on 10 cases of DF (including 4 cellular DF), 10 standard DFSP, and 2 AFL. The proliferation index and mitotic figures were counted per square millimeter in a “hotspot” (in a fashion similar to mitotic counts in melanoma). All cases of DF showed much higher Ki67 proliferation index (P = 0.0001) along with increased mitotic figures both on H&E and with anti-PHH3 (P = 0.0001) when compared to AFL/DFSP. Our data indicate that DF has a higher proliferation index and mitotic counts when compared to superficial/peripheral portion of AFL and DFSP. This finding may be helpful in the differential diagnosis among these fibrohistiocytic lesions.
*Department of Pathology, Baylor University Medical Center, Dallas, TX;
†Department of Pathology, Pathologist Biomedical Laboratories, Dallas, TX;
‡Department of Pathology, UF Health, Jacksonville, Jacksonville, FL;
§Department of Pathology, The University of Texas MD Anderson Cancer Center, Houston, TX; and
¶Department of Pathology, MD Anderson Cancer Center, Houston, TX.
Reprints: Dr. Victor Prieto, MD, PhD, Chair, Department of Pathology and Laboratory Medicine, University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, G1.3547a, Houston, TX 77030 (e-mail: vprieto@mdanderson.org).
The authors declare no conflicts of interest.
