Dermatofibrosarcoma protuberans — Viva

Q1: Definition and clinical presentation (2 min)

Q1.1. Define dermatofibrosarcoma protuberans (DFSP). A. A low-to-intermediate grade malignant fibroblastic tumour of skin. Locally aggressive; rarely metastasises in classic DFSP except in the fibrosarcomatous variant.^[1]

Q1.2. Describe the classic clinical evolution. A. Slow-growing, indurated plaque (often with an atrophic centre) that progresses over years to a multinodular protuberant mass, sometimes ulcerated. The 'protuberans' reflects the late stage.^[1]

^[1][4]Q1.3. What is the typical site distribution? A. Trunk about half, proximal extremities roughly a fifth to a third, head and neck roughly a tenth.^[1]

Q1.4. What is the peak age and sex distribution? A. Peak in the 30s to 40s with slight male predominance; higher incidence in patients with skin of colour.^[1]

Q1.5. What is the typical duration before diagnosis? A. Often present for years before diagnosis; the slow-growing lesion is often dismissed as a cyst, lipoma, keloid, scar, or dermatofibroma.^[1]

Q2: Differential diagnosis (3 min)

Q2.1. What is the single most important differential diagnosis, and how is it distinguished? A. Dermatofibroma (benign fibrous histiocytoma). Distinguished by: dimple sign (positive in DF, absent in DFSP); IHC — DF is CD34-/Factor XIIIa+, DFSP is CD34+/Factor XIIIa-; and molecular testing — DF has no COL1A1-PDGFB fusion; DFSP does.^[2]

Q2.2. What other entities should be considered in the differential? A. Keloid/hypertrophic scar; dermatomyofibroma; solitary fibrous tumour; desmoplastic melanoma; atypical fibroxanthoma; pleomorphic dermal sarcoma; cutaneous leiomyosarcoma; nodular fasciitis; morpheaform BCC; nodular melanoma — distinguish by site, growth rate, trauma history and the IHC panel in Q2.4.^[2]

^[2][3]Q2.3. A patient had a 'dermatofibroma' excised from the trunk 2 years ago and now has a recurrent nodule at the same site. What is the appropriate next step? A. Re-biopsy the recurrent nodule with CD34 and Factor XIIIa immunostaining to exclude DFSP. The original 'dermatofibroma' diagnosis on the trunk should be reconsidered - truncal location and recurrence are both red flags for DFSP. If DFSP is confirmed, manage with Mohs and consider imatinib for unresectable disease.^[2]

Q2.4. What is the IHC profile that closes the diagnosis of DFSP? A. CD34+ (strong, diffuse; HALLMARK). This profile excludes dermatofibroma and the other spindle-cell mimics listed in Q2.2.^[2]

Q3: Investigations (2 min)

Q3.1. What is the appropriate biopsy technique? A. Sample the most indurated area with a full-thickness biopsy that reaches the deep margin (punch or incisional technique); a superficial shave risks missing the deep component and the fibrosarcomatous areas. Mark the biopsy site for the surgeon.^[1]

Q3.2. Describe the classic histology. A. Monotonous storiform pattern of uniform spindle cells with minimal atypia and few mitoses; honeycomb (lace-like) infiltration of subcutaneous fat along connective-tissue septa; low proliferative index.^[1]

Q3.3. What is the molecular hallmark? A. A translocation fusing the COL1A1 and PDGFB genes, driving proliferation through PDGFR-beta signalling.^[2]

^[2][2]Q3.4. Which molecular test is the standard for confirmation? A. FISH for the COL1A1-PDGFB fusion is the standard; RT-PCR and NGS sarcoma panel are alternatives. Confirmation is mandatory before imatinib therapy.^[2]

^[2]Q3.5. What imaging is required for staging? A. MRI of the primary site for large lesions, recurrent disease, or suspected deep extension; CT chest for pulmonary metastases in fibrosarcomatous, large, or recurrent disease.^[1]

Q4: Management (3 min)

Q4.1. What is the standard-of-care surgical treatment for localised DFSP? A. Mohs micrographic surgery (MMS) is the standard of care, examining the full margin; wide local excision with 2–3 cm margins to the deep fascia with CD34 immunostaining of the margins is the alternative.^[1]

Q4.2. Why is Mohs preferred over standard WLE? A. DFSP has subclinical honeycomb infiltration extending beyond the clinical margin, which standard sectioning may miss at the periphery; Mohs examines the full margin and conserves tissue (critical for head/neck, distal extremities, and large lesions).^[1]

^[2][2]Q4.3. What systemic therapy is used for unresectable, recurrent, or metastatic DFSP, and what is its mechanism? A. Imatinib once daily (continuous; dose escalation for progression). Small-molecule tyrosine kinase inhibitor of PDGFR-beta; the target in DFSP is the PDGFR-beta encoded by the PDGFB portion of the fusion — see the local protocol for the exact dose. Approved for unresectable, recurrent, or metastatic DFSP.^[1]

^[2]Q4.4. What is neoadjuvant imatinib and when is it used? A. Imatinib given before surgery to shrink large or anatomically constrained tumours, with the goal of making them resectable with less morbidity. Widely used off-label; the optimal duration and long-term outcome are not well defined.

Q4.5. What is the role of radiotherapy? A. Adjuvant for positive margins after WLE when re-excision is not feasible, for unresectable primary disease, and as definitive therapy for inoperable FS-DFSP; improves local control after subtotal resection.^[1]

Q4.6. What is the follow-up schedule? A. Regular clinical review with imaging of the primary site; CT chest in fibrosarcomatous, large, or recurrent disease. Patient education on self-examination, photographic surveillance, and prompt review of any new nodule.^[1]

Q5: Complications and prognosis (2 min)

Q5.1. What is the most common complication? A. Local recurrence. Driven by subclinical extension that defeats standard WLE. Recurrence can be late as well as early; it is more frequent in head and neck DFSP and in fibrosarcomatous disease.^[1]

Q5.2. What is the metastatic risk? A. Rare in classic DFSP and substantially higher in FS-DFSP. The most common metastatic site is the lungs (haematogenous spread); lymph nodes can be involved (unusually for a sarcoma); bone is a late site.^[1]

^[2][2]Q5.3. What is the 5-year disease-specific survival? A. Excellent for localised disease; poor for metastatic disease (improving with imatinib).^[1]

Q5.4. List the prognostic factors in order of importance. A. Fibrosarcomatous transformation; positive margins after surgery; large size; head and neck location; deep invasion; and fusion variant (classic COL1A1-PDGFB predicts imatinib response).^[1]

^[2][2]Q5.5. What is fibrosarcomatous transformation, and how is it diagnosed? A. Higher-grade areas within a DFSP with increased cellularity and herringbone pattern; CD34 may be lost but the fusion persists. Management: wider margins, adjuvant radiotherapy, consider imatinib, CT chest staging.^[1]

^[2]Q5.6. What is the imatinib toxicity profile? A. Oedema, gastrointestinal upset, myelosuppression, hepatotoxicity, fatigue and muscle cramps are reported; monitoring of blood counts, liver and thyroid function is required — see the local protocol for the schedule. Drug interactions occur via CYP3A4.^[1]

Q6: Paediatric, pregnancy, and skin-of-colour scenarios (2 min)

Q6.1. What is giant cell fibroblastoma, and how is it related to DFSP? A. The paediatric equivalent of DFSP. Shares the COL1A1-PDGFB fusion, the CD34+ immunoprofile, and the locally infiltrative behaviour. The WHO 4th edition lists GCF and DFSP as a combined entity. A paediatric dermal/subcutaneous nodule with CD34+ spindle cells should raise GCF as well as DFSP.

Q6.2. How is DFSP managed in pregnancy? A. The lesion may enlarge rapidly in pregnancy. Mohs is feasible in the second trimester with appropriate positioning and obstetric support; systemic therapy decisions need obstetric input.^[1]

Q6.3. What is unique about DFSP in skin of colour? A. Higher incidence in patients with skin of colour; Bednar (pigmented) variant is more common.^[1]

Q7: Pearls and high-yield one-liners (2 min)

Q7.1. Give the one-liner definition of DFSP. A. A low-to-intermediate grade malignant fibroblastic tumour of skin, CD34+, storiform-cellular, with honeycomb fat infiltration, driven by a t(17;22) COL1A1-PDGFB fusion, treated with Mohs micrographic surgery (1 percent recurrence) or wide local excision with 2-3 cm margins (10-20 percent recurrence), and imatinib for unresectable, recurrent, or metastatic disease.

Q7.2. Give the one-liner that scores the DF vs DFSP distinction. A. DF is CD34-/FXIIIa+ with a dimple sign; DFSP is CD34+/FXIIIa- with an infiltrative plaque — Mohs or imatinib.^[2]

Q7.3. Give the one-liner that scores the molecular biology. A. t(17;22) COL1A1-PDGFB -> constitutive PDGFB -> autocrine PDGFR-beta activation -> RAS-MAPK and PI3K-AKT.

^[2]Q7.4. Give the one-liner that scores the Mohs rationale. A. DFSP has subclinical honeycomb infiltration; bread-loaf sectioning examines <1 percent of the margin; Mohs examines 100 percent.

Q7.5. Give the one-liner that scores the FS-DFSP clinical significance. A. FS-DFSP = 10-15 percent of cases, higher-grade with >5 mitoses per 10 HPF and herringbone pattern; CD34 may be lost but the fusion persists; metastatic risk 15-30 percent vs <5 percent in classic DFSP; treat aggressively.

^[1]Q7.6. Give the one-liner that scores the frequently-misremembered fact. A. Classic DFSP does NOT commonly metastasise (<5 percent); the FS variant does (15-30 percent); Mohs is the standard of care, NOT 4-5 cm WLE.

References4ShowHide

1. [1]Remiszewski P, et al. Dermatofibrosarcoma Protuberans (DFSP): Current Treatments and Clinical Trials Curr Treat Options Oncol, 2025.PMID 41042442
2. [2]Das S, et al. Beyond COL1A1::PDGFB: Rare fusions and their clinical implications in dermatofibrosarcoma protuberans World J Clin Cases, 2025.PMID 41356086
3. [3]Tillman BN, Liu JC. Cutaneous Sarcomas Otolaryngol Clin North Am, 2021.PMID 33602520
4. [4]Remiszewski P, et al. Dermatofibrosarcoma Protuberans (DFSP): Current Treatments and Clinical Trials Curr Treat Options Oncol, 2025.PMID 41042442