Other MalignanciesAdvanced · 7 min read

Atypical Fibroxanthoma (AFX) and Pleomorphic Dermal Sarcoma (PDS)

A rapidly enlarging red-pink dome on the bald scalp or forehead of an elderly fair-skinned patient; AFX and PDS sit on a continuum defined by depth, vascular and perineural invasion.

By Dr. Yehonatan KaplanPublished Updated

In brief

Atypical fibroxanthoma is a dermal pleomorphic spindle cell tumor of the chronically photodamaged elderly scalp and face, classically running an indolent course with metastatic risk under 1%. Pleomorphic dermal sarcoma represents the higher-grade counterpart: histologically similar but extending into subcutis, with vascular or perineural invasion, tumor necrosis, and metastatic risk in the 10 to 20% range. The two tumors share a UV-driven mutational signature, identical immunohistochemistry (CD10 positive, S100 negative), and a near-identical dermoscopic appearance, so the distinction rests on histology of the entire excised specimen.

Must-remember points

💡AFX and PDS share clinical and dermoscopic features; the distinction is histologic and depth-based, not visible at the chair side.
🔬Mandatory IHC: MART-1 or SOX10, S100, AE1/AE3 plus p63 or p40, plus desmin or SMA and CD34 to exclude melanoma, sarcomatoid SCC, leiomyosarcoma, and DFSP.
🩸Dermoscopy shows red structureless background, polymorphic vessels, ulceration, and shiny white areas; absence of pigmented structures.
🧬Both AFX and PDS carry UV-signature TP53, CDKN2A, NOTCH1/2, and FAT1 mutations, supporting a shared photodamage etiology.
✂️Mohs micrographic surgery is the surgical standard, with local recurrence under 5%; wide local excision needs 1 to 2 cm margins to fascia.
🩻PDS with subcutaneous, vascular, or perineural invasion warrants imaging and selective consideration of SLNB; AFX does not require staging.
📋Deep punch or excisional biopsy preferred over shave: superficial sampling can mask the subcutaneous component that defines PDS.

Clinical content

01Clinically AFX and PDS present as a solitary, rapidly enlarging red to red-pink dome-shaped or polypoid nodule, often ulcerated, on the bald scalp, ear, forehead, or dorsal hand of a fair-skinned patient over 70. Lesions are usually 1 to 2 cm at diagnosis and reported as growing over weeks to months. Background actinic damage, multiple AKs, and prior NMSC are nearly universal. The clinical differential includes amelanotic melanoma, BCC (especially nodular and basosquamous variants), SCC, Merkel cell carcinoma, pyogenic granuloma, and angiosarcoma, each of which can mimic AFX and must be excluded histologically.

02Dermoscopy of AFX and PDS is nonspecific but reproducible. The most consistent features are a red structureless background, polymorphic vessels (linear-irregular, dotted, hairpin, serpentine, sometimes arborizing), ulceration with hematogenous crust, and white scar-like or shiny white areas reflecting the dermal collagen of the tumor stroma. A whitish-pink or porcelain-white perimeter has been reported. Pigmented structures and pigment network are absent. As with MCC and amelanotic melanoma the dermoscopic call is malignant amelanotic tumor, and biopsy is mandatory.

03Histopathology shows sheets and fascicles of pleomorphic spindle and epithelioid cells with marked nuclear atypia, atypical mitoses (often more than 10 per high-power field), and giant cells. AFX is confined to the dermis and abuts but does not significantly invade subcutis. PDS by definition shows substantial subcutaneous extension, lymphovascular invasion (LVI), perineural invasion (PNI), or tumor necrosis, any one of which upgrades AFX to PDS. Both tumors are typically larger and more deeply infiltrative than they appear clinically.

04Immunohistochemistry is essential because diagnosis is one of exclusion. The classic panel is MART-1 / SOX10 (negative; excludes spindle cell or desmoplastic melanoma), S100 (negative; excludes melanoma and most malignant peripheral nerve sheath tumors), p63 / p40 and pan-cytokeratin AE1/AE3 (negative; excludes sarcomatoid SCC), and CD34 / desmin / smooth muscle actin (typically negative; excludes leiomyosarcoma and DFSP). CD10, CD68, CD99, and procollagen-1 are usually positive but are not specific. UV-signature TP53 mutations are present in nearly all AFX and PDS, supporting a shared origin.

05AFX vs PDS distinction matters for prognosis and follow-up. Series consistently report AFX 5-year disease-specific survival above 95% with metastatic risk under 1%, while PDS has metastatic risk in the 10 to 20% range, most commonly to regional lymph nodes, lung, and skin. Local recurrence rates of 5 to 16% (AFX) and up to 28% (PDS) are reported with standard excision; Mohs micrographic surgery brings local recurrence under 5%.

06Surgical management favors Mohs for both AFX and PDS when feasible, given the elderly patients, scalp and facial location, and cosmetic constraints. Wide local excision with 1 to 2 cm margins to fascia is the alternative. For PDS, additional staging with cross-sectional imaging (CT or MRI) and consideration of sentinel lymph node biopsy on a case-by-case basis is reasonable, although evidence for routine SLNB is limited. Adjuvant radiotherapy is considered for incompletely resected or high-risk PDS.

07Differential diagnosis on biopsy is the central pitfall. Sarcomatoid (spindle cell) SCC may show focal cytokeratin positivity that AFX lacks, so deep blocks and multiple cytokeratin antibodies (CK5/6, AE1/AE3, MNF116, p63, p40) should be examined before settling on AFX. Spindle cell or desmoplastic melanoma can be S100 weak or focal; SOX10 is typically retained and helps separate it from AFX. Leiomyosarcoma is desmin or SMA positive, and angiosarcoma stains for CD31, ERG, and sometimes MYC.

Key dermoscopic features

Red structureless background
Most consistent dermoscopic substrate of AFX and PDSDiffuse pinkish-red hue replacing skin marks across most of the lesion
Polymorphic vessels
Hallmark of malignant amelanotic tumor; nonspecificCoexisting linear-irregular, dotted, hairpin, serpentine, and sometimes arborizing vessels
Ulceration with hematogenous crust
Common in rapidly growing or larger AFX and PDSStructureless red to red-black areas with overlying brown-red crust
White scar-like or shiny white areas
Reflects dermal collagenous stroma of the tumorPorcelain-white structureless areas, sometimes peripheral, polarization-dependent
Whitish-pink halo
Reported in some AFX cases at the lesion marginFaint white-pink rim surrounding the central red dome
Absence of pigmented structures
Distinguishes AFX/PDS from pigmented BCC and melanomaNo pigment network, no globules, no streaks, no blue-grey nests
Dome-shaped, often polypoid silhouette
Clinical-dermoscopic clue; matches rapid expansionRaised, broad-based or polypoid lesion with smooth or eroded surface
Background photodamage
Field effect supports UV-driven originSolar lentigines, AKs, scarring around the index lesion on the bald scalp or forehead

High yield clinical points15 pearls in 5 groups

Recognition & pattern analysis

3 points
1
Dermoscopy cannot separate AFX from PDS or from amelanotic melanoma. Red structureless areas, polymorphic vessels, ulceration, and shiny white areas are shared. Histology of the entire specimen is the only reliable separator.
2
AFX and PDS are diagnoses of exclusion. Mandatory IHC panel includes MART-1 or SOX10, S100, AE1/AE3 plus p63 or p40, and at least one smooth muscle marker (desmin or SMA) and CD34. Skipping any of these risks calling a sarcomatoid SCC or spindle cell melanoma an AFX.
3
UV-signature TP53 unifies AFX and PDS. Sequencing studies show C to T transitions at dipyrimidines in nearly all AFX and PDS, mirroring the UV signature seen in cutaneous SCC and supporting their shared photodamage etiology.

Diagnostic criteria & thresholds

1 point
1%
Subcutaneous invasion upgrades AFX to PDS. By current consensus criteria, any of subcutaneous extension, LVI, PNI, or tumor necrosis converts an AFX diagnosis to PDS, with metastatic risk rising from under 1% to roughly 10 to 20%.

Pitfalls & mimics

5 points
1
Shave biopsy may miss the diagnosis. Deep punch or excisional biopsy is preferred so the dermal-subcutaneous interface is sampled. A superficial shave can show only the dermal AFX-like component and miss the subcutaneous PDS component.
2
Stage PDS, do not stage AFX. PDS warrants cross-sectional imaging (CT or MRI of the tumor bed and chest) given metastatic potential. AFX in a typical scalp location with clean margins does not require imaging.
3
Beware sarcomatoid SCC mimicry. Rare cytokeratin positivity, p63 or p40 staining, or in situ SCC at the surface upgrades the diagnosis to sarcomatoid SCC, which carries higher metastatic risk and changes management.
4
Spindle cell melanoma is the other big mimic. Patchy or weak S100 or SOX10 staining argues for spindle cell or desmoplastic melanoma rather than AFX. Multiple deeper levels and additional melanocytic markers (e.g., MITF) help in equivocal cases.
5
Avoid premature reassurance. An AFX label on a small biopsy with clean superficial dermal disease may underestimate a deeper PDS component. Re-examine the full specimen and discuss reclassification if subcutaneous extension is later identified.

When to biopsy

5 points
1
Bald scalp dome of an elderly fair-skinned patient is AFX or PDS until proven otherwise. The clinical phenotype is so typical that any rapidly growing red dome on the photodamaged scalp or face should trigger excisional biopsy with deep margins, not shave biopsy alone.
5%
Mohs is the surgical gold standard. Reported local recurrence with Mohs is under 5% for AFX and substantially better than wide local excision for PDS. Mohs is preferred for elderly scalp and facial lesions.
3
Wide local excision needs deep margins. If Mohs is unavailable, wide local excision with 1 to 2 cm margins down to and including fascia gives the best chance of complete clearance, especially when subcutaneous invasion is suspected.
4
Sentinel node biopsy in PDS is selective. Routine SLNB is not standard for PDS due to limited evidence, but it can be considered in larger tumors with extensive subcutaneous, vascular, or perineural invasion, ideally within a multidisciplinary discussion.
5
Adjuvant radiotherapy for high-risk PDS. For PDS with positive margins not amenable to re-excision, extensive PNI or LVI, or recurrent disease, adjuvant radiation is considered to reduce local recurrence.

Follow-up & monitoring

1 point
1
Recurrence is the most common adverse event. Local recurrence drives morbidity in AFX, while PDS combines local recurrence with regional and distant spread. Long-term clinical surveillance every 3 to 6 months for the first 2 years is reasonable.

Lectures covering this topic3 lectures

Excellence Intl 2025DE-INTL · #05
Rare Skin Tumors
Giuseppe Argenziano
Excellence PracticalDE-PRACT · #06
Rare Malignancy Cases - MCC, Sarcomas, Adnexal
Giuseppe Argenziano and Aimilios Lallas
Academy 2025ACAD25 · #12
Rare Skin Tumors
Giuseppe Argenziano

Notable updates & conceptual milestones5 updates

Consensus criteria distinguishing AFX from PDS

2012

Miller and colleagues (2012, Br J Dermatol) operationalized the AFX-PDS distinction using subcutaneous invasion, lymphovascular or perineural invasion, and tumor necrosis as upgrading features. These criteria are now used in WHO classifications and clinical pathways.

Whole-exome sequencing of AFX and PDS

2018

Studies (Griewank 2018, J Invest Dermatol) showed UV-signature mutations in TP53, CDKN2A, NOTCH1/2, and FAT1 in both AFX and PDS, supporting their position on a single biologic continuum and explaining the shared photodamage etiology.

Mohs micrographic surgery as standard of care

2015-2026

Pooled outcome data demonstrate local recurrence rates under 5% with Mohs for AFX and PDS, substantially lower than with wide local excision. Mohs is now considered first-line surgical management at most academic centers, particularly for scalp and facial lesions.

Immunohistochemistry expansion (CD10, procollagen-1, LN-2)

2010-2026

While CD10 remains the most useful exclusion-style marker, additional markers including procollagen-1 and LN-2 have been described to support AFX/PDS diagnosis in difficult cases, although none is fully specific. Diagnosis still relies on excluding melanoma, SCC, and other sarcomas.

Reflectance confocal microscopy and OCT for surgical planning

2020-2026

Single-center reports describe RCM and OCT mapping of AFX and PDS to assess depth and lateral extension before Mohs, although routine clinical use is limited and histology remains the standard.

Bottom line

AFX and PDS form a single UV-driven biologic continuum that presents as a rapidly growing red dome on the photodamaged scalp or face of an elderly patient. Dermoscopy is suggestive but not specific, and accurate classification depends on full-thickness histology with a defined IHC panel that excludes melanoma, sarcomatoid SCC, and other sarcomas.

Refined molecular markers and copy-number profiles are positioned to standardize the AFX-PDS boundary and identify high-risk PDS variants. Optimization of margin assessment with Mohs combined with imaging-guided staging (and selective adjuvant radiation or sentinel node biopsy for PDS) is expected to improve oncologic outcomes while preserving function in elderly patients.

References

Sources cited in the lecture content or that underpin the clinical points above. Verify with primary sources before practice changes.

  1. [1]
    Miller K, Goodlad JR, Brenn T. Pleomorphic dermal sarcoma: adverse histologic features predict aggressive behavior and allow distinction from atypical fibroxanthoma. Am J Surg Pathol. 2012;36(9):1317-1326.
    PubMed: 22510760DOI: 10.1097/PAS.0b013e31825359e1· Operationalized the histologic distinction between AFX and PDS based on subcutaneous invasion, lymphovascular or perineural invasion, and tumor necrosis.
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    Iorizzo LJ 3rd, Brown MD. Atypical fibroxanthoma: a review of the literature. Dermatol Surg. 2011;37(2):146-157.
    PubMed: 21269345DOI: 10.1111/j.1524-4725.2010.01843.x· Comprehensive review of clinical and histologic features, treatment outcomes, and prognosis of AFX.
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    Griewank KG, Wiesner T, Murali R, et al. Atypical fibroxanthoma and pleomorphic dermal sarcoma harbor frequent NOTCH1/2 and FAT1 mutations and similar DNA copy number alteration profiles. Mod Pathol. 2018;31(3):418-428.
    PubMed: 29099504DOI: 10.1038/modpathol.2017.146· Whole-exome and copy-number analysis showing shared UV-signature mutational profile of AFX and PDS.
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    Moscarella E, Piana S, Specchio F, et al. Dermoscopy features of atypical fibroxanthoma: A multicenter study of the International Dermoscopy Society. Australas J Dermatol. 2018;59(2):309-311.
    PubMed: 29569417DOI: 10.1111/ajd.12783· Multicenter dermoscopy series describing red structureless areas, polymorphic vessels, ulceration, and shiny white structures as the most reproducible findings.
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    Tolkachjov SN, Kelley BF, Alahdab F, Erwin PJ, Brewer JD. Atypical fibroxanthoma: Systematic review and meta-analysis of treatment with Mohs micrographic surgery or excision. J Am Acad Dermatol. 2018;79(5):929-934.e6.
    PubMed: 29981390DOI: 10.1016/j.jaad.2018.06.048· Meta-analysis demonstrating lower local recurrence with Mohs (around 2%) compared with wide local excision (around 8%) in AFX.
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    Persa OD, Loquai C, Wobser M, et al. Extended surgical safety margins and ipsilateral lymph node biopsies for pleomorphic dermal sarcomas. Br J Dermatol. 2019;181(2):343-348.
    · Outcomes of extended margin excision and selective sentinel lymph node biopsy in pleomorphic dermal sarcoma.