This video presents a detailed pathological review of a Dermatofibrosarcoma Protuberans (DFSP), showcasing a classic example of this challenging spindle cell tumor. The key diagnostic feature highlighted is the highly pronounced storiform pattern (swirling, pinwheeling arrangement of cells) coupled with the characteristic clean fat entrapment (honeycomb pattern) in the subcutaneous tissue. The speaker systematically addresses crucial entities in the differential diagnosis, contrasting DFSP (bland, monotonous, CD34+) against Dermatofibroma (plumper cells, atypia, often CD34-), Solitary Fibrous Tumor (SFT), and Perineurioma. The molecular pathology is emphasized, noting DFSP's defining Collagen 1A1-PDGFB translocation and the use of STAT6 as a specific marker for SFT (NAB2-STAT6 translocation) in differentiating these tumors.
Dermatofibrosarcoma Protuberans (DFSP) Case Review
0:16 Spindle Cell Tumor Difficulty: The speaker acknowledges that spindle cell tumors are universally challenging, even for specialists.
0:53 Perfect Storiform Pattern: The case features a classic and "most perfect" example of the storiform pattern—a swirling, whirling, pinwheeling arrangement of cells that is difficult to describe but unmistakable upon viewing.
1:37 Cytological Features: DFSP cells are typically bland, thin, elongated spindle cells, which appear flat or "pancake-like" depending on the plane of section.
2:24 Diagnosis and Key Features: The tumor is confirmed as Dermatofibrosarcoma Protuberans (DFSP), characterized by bland spindle cells, storiform pattern, and clean fat entrapment (honeycomb pattern) in the subcutis.
3:19 Invasion Pattern Takeaway: DFSP classically invades fat aggressively, often completely replacing the adipocytes, leaving only small islands of trapped fat cells at the edges (4:06).
4:47 Differential Diagnosis: Dermatofibroma (DF): DF is differentiated by features usually absent in DFSP, including epidermal hyperplasia, plumper/larger cells, scattered atypia, hemorrhage/hemosiderin, foam cells, and multinucleated giant cells.
5:44 DF vs. DFSP Stains (CD34): DFSP is typically strongly and diffusely positive for CD34, while DF is usually negative. Collagen trapping, common in DF, can occasionally be seen in DFSP.
6:06 Pigmented DFSP: DFSP that contains melanin pigment (from dendritic melanocytic cells) is called a Bednar tumor (a pigmented variant).
8:14 Differential Diagnosis: Solitary Fibrous Tumor (SFT): SFT is included in the differential because it is also CD34 positive and can show dilated, branching, "Staghorn" vessels—a feature sometimes seen in DFSP.
10:05 SFT Specific Marker (STAT6): To distinguish SFT from DFSP, the highly specific nuclear stain STAT6 is used (positive in SFT, negative in DFSP). SFT is defined by a NAB2-STAT6 translocation.
11:37 Differential Diagnosis: Perineurioma: Perineurioma can mimic DFSP due to its whirling/swirling growth pattern. Perineurioma expresses markers like EMA, GLUT1, and Claudin-1, but staining is often weak or patchy.
12:56 DFSP Molecular Hallmark: The classic translocation in DFSP is the fusion of Collagen 1A1 and PDGFB (Platelet-Derived Growth Factor Beta). A newer, alternate fusion involving PDGFD (Delta) has also been reported (13:18).
13:48 Case Conclusion: The current case is histologically classic, meaning molecular testing (FISH) is likely unnecessary for confirmation.