This transcript features a pathologist discussing the histopathological features and differential diagnosis of Dermatofibrosarcoma Protuberans (DFSP). The discussion centers around the characteristic "story form" growth pattern observed in the bland, thin, elongated spindle cells of DFSP, emphasizing that this pattern is the most reliable diagnostic clue. The speaker also details associated features like honeycomb fat entrapment and notes that DFSP cells can sometimes appear oval when viewed from a different angle ("oval shaped pancakes"). A significant portion of the video is dedicated to differentiating DFSP from other spindle cell lesions, primarily Dermatofibroma, Solitary Fibrous Tumor (SFT), and Perineurioma. Key distinguishing features, including immunohistochemical markers (CD34 positivity for DFSP and SFT; Factor 13A positivity for Dermatofibroma), cellular morphology (atypia in Dermatofibroma vs. blandness in DFSP), and characteristic translocations (COL1A1-PDGFB for DFSP and STAT6 for SFT), are reviewed. The speaker also mentions an emerging alternative fusion involving PDGFD in DFSP.
Dermatopathology Deep Dive: Distinguishing Dermatofibrosarcoma Protuberans (DFSP)
0:00:16 Spindle Cell Tumor Confirmation: The initial finding confirms the presence of a spindle cell tumor, noting their diagnostic difficulty even for experienced pathologists.
0:00:48 "Story Form" Pattern: The key diagnostic feature of the lesion is the "story form pattern," described as cells stacked in lines that swirl and whirl, representing the classic growth architecture of DFSP.
0:01:37 Cell Morphology: The cells are bland, thin, and elongated spindle cells; they can appear oval when viewed 90 degrees from their thin presentation.
0:02:20 Diagnosis: DFSP: The lesion in question is identified as Dermatofibrosarcoma Protuberans (DFSP).
0:03:00 Key DFSP Features: Characteristics include bland spindle cells, story form pattern, honeycomb pattern of fat entrapment, and general lack of significant inflammation.
0:03:19 Aggressive Fat Invasion: DFSP can extensively infiltrate subcutaneous fat, sometimes leaving only small "islands of stranded fat" at the periphery.
0:03:40 Locating Dermal-Subcutaneous Junction: Eccrine coils are used as a landmark to identify the deep dermis/superficial subcutis junction, helping determine the expected boundary of fat involvement.
0:04:47 Differential Diagnosis Introduction: Other lesions to consider include Dermatofibroma, Diffuse Neurofibroma, Solitary Fibrous Tumor (SFT), and Perineurioma.
Dermatofibroma: Usually shows epidermal hyperplasia/acanthosis, plumper cells, more abundant cytoplasm, rounded nuclei, scattered atypia, hemorrhage, hemosiderin, and Factor 13A positivity.
DFSP: Typically bland, monotonous, elongated cells, lacks epidermal change, and stains strongly/diffusely positive for CD34.
0:06:14 Pigmented Variant: DFSP with melanin pigment is called a "Bednar Tumor," which is clinically insignificant compared to standard DFSP.
0:06:32 Collagen Trapping: While common in Dermatofibroma, collagen trapping can occasionally be seen in DFSP, making it an unreliable sole distinguishing feature.
0:08:06 Solitary Fibrous Tumor (SFT) Mimicry: SFT can mimic DFSP due to haphazard swirling and the presence of dilated vessels (sometimes staghorn-like). Both express CD34.
0:10:10 Specific Marker for SFT: STAT6 nuclear staining is a more specific marker for SFT (due to the NAB2-STAT6 fusion) and should be negative in DFSP.
0:11:37 Perineurioma Mimicry: Perineuriomas can mimic the swirling pattern of DFSP but express perineurial markers like EMA and GLUE-1 (though staining can be weak/finicky).
0:12:55 DFSP Translocation: The vast majority of DFSP cases involve the COL1A1-PDGFB translocation.
0:13:16 New DFSP Fusion: A recently discovered alternative fusion involves PDGFD (e.g., PDGFD-CCDC6).
0:13:48 FISH Testing: Molecular testing (FISH) is reserved for truly difficult cases, as the classic histologic features and key markers often suffice for diagnosis.