Dermatofibrosarcoma Protuberans - A Diagnostic Dilemma on Cytology

INTRODUCTION

Dermatofibrosarcoma protuberans (DFSP) is a relatively uncommon soft tissue sarcoma arising from the dermis and subcutaneous tissue and is characterised by intermediate malignant potential with a pronounced tendency for local recurrence.^[1-3] The tumour typically demonstrates slow, infiltrative growth and may initially present as an indurated plaque before progressing to a nodular or protuberant mass. DFSP accounts for approximately 0.1% of all malignant neoplasms and nearly 1% of mesenchymal tumours. It most frequently affects young to middle-aged adults and shows a predilection for the trunk and proximal extremities. Historically, DFSP was referred to as keloid sarcoma, a term later replaced following its formal description by Hoffman in 1925.^[1,4]Histochemical, ultrastructural, and immunophenotypic studies support a fibroblastic lineage, with diffuse CD34 expression suggesting derivation from dermal dendritic cells.^[5]

Fine-needle aspiration cytology (FNAC) is an initial diagnostic modality for superficial soft tissue lesions due to its simplicity, rapid turnaround, and minimally invasive nature. FNAC may provide an early diagnostic clue in suspected DFSP, particularly in recurrent or superficial lesions.^[6] However, because of significant overlap in cytomorphological features with other spindle cell tumours, FNAC findings alone are often insufficient for definitive diagnosis, necessitating histopathological evaluation supported by immunohistochemistry.

CASE REPORT

A 25-year-old female presented to the surgical outpatient department with a gradually enlarging swelling over the right flank that had been present for six months. On clinical examination, a well-circumscribed, non-tender, reddish-purple, solid-cystic lesion measuring approximately 2.5 × 2 cm was noted [Figure 1a]. Ultrasonography revealed a necrotic cystic lesion in the subcutaneous plane of the right flank measuring approximately 2.8 × 2.5 × 0.9 cm, with no evidence of internal vascularity, raising suspicion of a neoplastic aetiology. FNAC was subsequently advised.

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Figure 1a: Clinical photograph showing a purple-red soft tissue subcutaneous swelling measuring 2x2cm on the right flank.

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Fine-needle aspiration was performed using a 23-gauge needle, and the aspirated material was processed for cytological evaluation. Wet-fixed smears were stained with Haematoxylin and Eosin, while air-dried smears were stained with May–Grünwald–Giemsa. Microscopic examination revealed a highly cellular lesion composed of loosely cohesive clusters and dispersed spindle-shaped cells arranged predominantly in a storiform pattern. The tumour cells exhibited mild to moderate nuclear pleomorphism, elongated nuclei with evenly distributed chromatin, inconspicuous nucleoli, scant cytoplasm, and indistinct cell borders. The background showed fragments of collagenous stroma with minimal inflammatory infiltrate, and occasional mitotic figures were identified [Figure 1b-d]. Based on these cytological features, a spindle cell neoplasm of low malignant potential was suggested, with DFSP considered a likely possibility. Histopathological examination and immunohistochemical analysis were advised for confirmation.

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Figure 1b: Fine needle aspiration smear showing loosely cohesive aggregates of spindle cells (Haematoxylin and eosin, 10x)

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Figure 1c: Fine needle aspiration smear showing clusters of spindle cells with plump nuclei (May-Grünwald-Giemsa stain, 10x).

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Figure 1d: Fine needle aspiration smear showing spindle shaped cells with elongated to plump nuclei, evenly distributed chromatin, regular nuclear outline and scanty cytoplasm (May-GrünwaldGiemsa stain, 40x)

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The lesion was subsequently excised and submitted for histopathological evaluation. Gross examination revealed a circumscribed grey, white tumour with an attached skin ellipse measuring approximately 3 cm in greatest dimension [Figure 2a]. The cut surface was homogeneous and grey, white. Microscopic examination demonstrated an infiltrative spindle cell tumour involving the dermis, arranged in a characteristic storiform pattern. The tumour cells showed mild pleomorphism, ovoid to elongated nuclei with vesicular chromatin, and moderate eosinophilic cytoplasm embedded within a collagenous matrix [Figure 2b and c]. Immunohistochemical analysis revealed diffuse CD34 positivity [Figure 2d], while the tumour cells were negative for transducin-like enhancer protein (TLE1), cytokeratin, S-100, and p63, confirming the diagnosis of DFSP. The patient is currently under regular follow-up and remains clinically stable.

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Figure 2: (a) Gross examination of the specimen showing a globular grey white lesion. (b) Histopathological section with normal epidermis, grenz zone in the dermis with the deep dermis showing spindle cells arranged in a storiform pattern (H&E, 10x); (c) High power view showing storiform arrangement of spindle cells in the deep dermis (H&E, 40x); (d) Immunohistochemistry with tumour cells showing positivity for CD34)

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DISCUSSION

DFSP predominantly affects young adults and demonstrates a slight male predominance.^[1] The trunk and proximal extremities represent the most commonly involved anatomical sites.^[4] The histogenesis of DFSP has been attributed to fibroblastic or fibrohistiocytic differentiation. At the molecular level, DFSP is characterised by a recurrent t(17;22) chromosomal translocation that results in the formation of the COL1A1–PDGFB fusion gene.^[3,6]This genetic alteration leads to constitutive activation of the platelet-derived growth factor receptor beta signalling pathway, driving tumour proliferation and local invasiveness.

Imaging modalities play an important role in disease assessment and surgical planning. Ultrasonography typically reveals a hypoechoic superficial mass, while magnetic resonance imaging is useful for evaluating tumour size, depth, and infiltration into adjacent structures. Cytological diagnosis of DFSP remains challenging because of considerable morphological overlap with other spindle cell tumours. Differential diagnoses include dermatofibroma, nodular fasciitis, fibromatosis, solitary fibrous tumour, peripheral nerve sheath tumours, synovial sarcoma, fibrosarcoma, and myxoid undifferentiated pleomorphic sarcoma.^[7,8]

Nodular fasciitis is usually smaller, rapidly growing, and exhibits a myxoid background with pleomorphic cells. Solitary fibrous tumour typically presents as a deep-seated lesion with uniform spindle cells arranged in fascicles or a patternless architecture. Peripheral nerve sheath tumours often show spindle cell fascicles with nuclear palisading and Verocay body formation. Fibrosarcoma demonstrates spindle cells arranged in long fascicles with a characteristic herringbone pattern and greater cytological atypia. In contrast, DFSP shows relatively monomorphic spindle cells arranged in a storiform pattern with prominent collagenous stroma.^[9,10]

Cell block preparation combined with immunohistochemistry can enhance diagnostic accuracy even in cytological specimens. Diffuse CD34 positivity, along with the absence of S-100 protein, is particularly helpful in confirming DFSP and excluding histological mimics.^[10,11] Histopathological examination remains the cornerstone of diagnosis, typically demonstrating infiltrative spindle cells arranged in a storiform pattern with low mitotic activity and extension into subcutaneous tissue.^[11] Although DFSP rarely metastasizes, local recurrence is common, especially when surgical margins are inadequate. Fibrosarcomatous transformation is associated with increased mitotic activity, reduced CD34 expression, and a worse prognosis.

CONCLUSION

FNAC serves as a valuable preliminary diagnostic tool for DFSP by identifying characteristic spindle cell morphology and architectural patterns. However, due to subtle cytological features and significant overlap with other spindle cell tumours, definitive diagnosis requires histopathological confirmation supported by immunohistochemistry. Early recognition of DFSP enables timely surgical intervention, with complete excision being essential for optimal local disease control and prevention of recurrence.