The locally invasive soft-tissue sarcoma, dermatofibrosarcoma protuberans (DFSPs), shares certain histologic features of the much more common and benign dermatofibroma (DF). While immunohistochemical stains, specifically cluster of differentiation 34 and Factor XIIIa, can be used to distinguish the 2 entities using microscopy, these markers are not entirely sensitive nor specific. Three-dimensionally, DFSP nuclei resemble a "puck" or "coin"-like shape. As hematoxylin/eosin-stained slides are prepared, these "puck" nuclei are fixed in an infinite number of orientations depending on their current position in rotation about their axes within the tumor cells. Under histological examination, this random nuclear positioning produces the appearance of 2 predominate morphologies: an ovoid "disk" shape (en face) and a narrow spindled shape (side view), which distribute in a roughly 50:50 ratio throughout the tumor sample slide. Nuclear morphology was analyzed in 324 DFSP and DF samples at high magnification (×400) to determine the presence or absence of a predominant morphology in which nuclei appear to alternate between an ovoid (en face) and spindled (side view) throughout most of the tumor sample. An alternating ovoid-spindled nuclear morphology was the predominant cytology in 98% of DFSP and was not predominant in 100% of DF samples (P < 0.001). This morphology was found to be highly specific (Sp = 1) and sensitive (Sn = 0.98) for DFSP. This unique nuclear morphology may be a more sensitive and specific diagnostic tool in identifying DFSP from DF in comparison with costly immunohistochemical stains.
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