Pleomorphic Dermal Sarcoma: Diagnosis, Treatment & Prognosis

Pleomorphic dermal sarcoma (PDS) is a rare but increasingly recognized skin cancer that arises most often on the chronically sun-damaged skin of older adults, particularly on the head and scalp. It belongs to a spectrum of tumors that includes atypical fibroxanthoma (AFX), its less aggressive relative, and carries a meaningful risk of local recurrence and, in a minority of cases, distant spread. Because PDS has only recently been established as a distinct diagnostic entity, there are no universally standardized guidelines for its workup or management, which means treatment decisions often borrow from the broader soft-tissue sarcoma playbook while being tailored to the tumor’s unique behavior.

Who Gets PDS and What It Looks Like

PDS overwhelmingly affects elderly, fair-skinned individuals with a history of heavy cumulative sun exposure. The typical patient is a man in his seventies or eighties who notices a firm, rapidly growing nodule on the scalp, forehead, ear, or another sun-exposed area. The lesion often ulcerates and can bleed easily, which is part of what prompts medical attention. Case reports describe presentations ranging from a lump on the arm to masses on the posterior trunk, but the head and neck remain the most common sites by a wide margin.¹

Ultraviolet radiation is the dominant risk factor. PDS carries a genetic UV damage signature, meaning its mutations reflect the cumulative toll of decades of sun exposure rather than a single inherited defect.² Immunosuppression is the other major contributor. In one cohort study, roughly 30% of patients with AFX or PDS were immunosuppressed. Among those, patients with underlying blood cancers had significantly higher rates of tumor progression and distant metastasis.² Organ transplant recipients on chronic anti-rejection drugs also fall into this higher-risk group, though less data exists specifically for PDS in that population.

How PDS Is Distinguished From Atypical Fibroxanthoma

This is one of the trickier aspects of the diagnosis. Under the microscope, PDS and AFX look strikingly similar: both are spindle-cell tumors made up of bizarre, irregularly shaped cells. The critical distinction comes down to depth of invasion and the presence of high-risk features. AFX is, by definition, a tumor confined to the dermis. Once the tumor invades the subcutaneous fat, or shows features like necrosis, perineural invasion (tumor growing along nerves), or vascular invasion (tumor inside blood vessels), it is reclassified as PDS.³

Making this distinction reliably requires examining the entire excised tumor, not just a small biopsy sample. A superficial biopsy might show only the AFX-like portion while missing deeper invasion that would change the diagnosis to PDS. One study on Mohs surgery specimens emphasized that systematic examination of the full debulk specimen is essential to properly separate the two entities.⁴ The practical consequence for patients is that a punch biopsy alone cannot definitively rule PDS in or out; the final pathology after complete removal is what settles the diagnosis.

The relationship between AFX and PDS has been debated, but growing evidence points to a disease spectrum rather than two entirely separate cancers. Molecular sequencing confirms overlapping mutation patterns, and PDS has been described as an AFX-like tumor with additional aggressive histologic features such as necrosis and vascular invasion.⁵ Think of AFX as the lower end of the spectrum and PDS as the higher end, with the boundary defined by how deeply and aggressively the tumor has grown.

The Role of Immunohistochemistry

Because PDS is a diagnosis of exclusion, pathologists rely heavily on immunohistochemical staining panels to rule out other cancers that can look similar under the microscope. The list of mimics is long: poorly differentiated squamous cell carcinoma, melanoma, leiomyosarcoma, and angiosarcoma can all present as spindle-cell tumors in the skin. To sort through these, labs routinely apply markers for epithelial cells, melanocytes, smooth muscle, and blood-vessel lining cells. Both AFX and PDS are typically negative for all of these, which is what confirms the diagnosis.⁶ CD10 positivity and the absence of markers like cytokeratins, S100, desmin, and CD31 are part of the standard diagnostic panel.³

In plain terms, PDS is identified less by what it is and more by what it is not. The staining panel exists to systematically eliminate other diagnoses. If the tumor is negative across the board for those marker categories and shows the right morphological features with subcutaneous invasion or high-risk characteristics, PDS is what remains.

Genomic Profile

Molecular sequencing has revealed that PDS tumors carry an exceptionally high mutational burden, consistent with decades of UV-induced DNA damage. The most consistently altered gene is TP53, with inactivating mutations found in essentially all tumor specimens studied. Frequent mutations also appear in CDKN2A, the TERT promoter, and NOTCH1.⁵ These are genes involved in cell-cycle control and tumor suppression, and their loss helps explain the tumor’s unchecked growth.

More recent work using broader sequencing panels has confirmed this core mutation pattern while also identifying differences in less common genes. PDS tumors showed a divergent distribution of alterations in genes involved in new blood vessel formation, DNA repair, and cell migration, which may help explain why PDS behaves more aggressively than AFX despite sharing much of the same mutational backbone.⁷ The high mutational burden also has potential therapeutic relevance: tumors with lots of mutations sometimes respond well to immune checkpoint inhibitors, a point that has generated interest in immunotherapy for PDS.

Diagnostic Workup and Staging

There are no PDS-specific staging guidelines, so clinicians generally follow the approach used for other soft-tissue sarcomas. The typical sequence begins with imaging of the primary tumor site using CT or MRI to determine the extent of local invasion, followed by a biopsy if one has not already been performed.⁸ Once PDS is confirmed, a metastatic workup is standard, and a CT scan of the chest is the most critical component because the lungs are the most common site of distant spread.⁸

In practice, the extent of the workup varies by institution. Some centers perform a staging CT of the chest without contrast at diagnosis and then switch to screening chest X-rays during follow-up.⁹ Others go further with PET-CT scans and MRI for larger or higher-risk tumors, particularly when there is concern about deep invasion near major structures.¹⁰ The lack of formal guidelines means that staging decisions are often driven by clinical judgment and the individual tumor’s characteristics.

Surgical Treatment

Surgery is the cornerstone of PDS treatment. The two main approaches are wide local excision (WLE), where the surgeon removes the tumor with a broad margin of surrounding tissue, and Mohs micrographic surgery, where thin layers are removed and examined under a microscope in real time until no cancer cells remain at the edges. Both methods aim to achieve clear margins, which is the single strongest predictor of a good outcome.

A study comparing the two approaches found no difference in survival between patients treated with Mohs surgery and those treated with wide local excision.¹¹ Mohs surgery does have the advantage of sparing more healthy tissue, which matters a great deal on the scalp and face where cosmetic and functional outcomes are a concern. On the other hand, wide local excision allows the full specimen to be examined by a dermatopathologist, which is important for confirming the PDS diagnosis and evaluating features like depth of invasion and necrosis. Some centers use a hybrid approach: Mohs surgery to clear the margins, with the debulk specimen sent separately for complete pathological assessment.⁴

Regardless of the surgical technique, incomplete excision is a significant risk factor for local recurrence. One review estimated local recurrence rates around 20–30% when margins are positive, compared to single-digit rates when margins are clear.¹² A series of scalp PDS cases reported a recurrence rate of 7% after primary resection with clear margins.¹³ The message is consistent: achieving clear surgical margins is the most controllable factor in reducing recurrence.

When Radiation Therapy Is Added

Adjuvant radiotherapy, meaning radiation given after surgery, is not routine for every PDS patient but is increasingly considered when risk factors for recurrence are present. The strongest signal for benefit comes in patients whose surgical margins are narrow, defined in most studies as less than two centimeters. In one cohort, patients who received adjuvant radiation after narrow-margin surgery had a mean local recurrence-free survival of 30 months compared to 19 months for those who had surgery alone, though this difference did not quite reach conventional statistical significance.¹⁴ Roughly 85% of patients who received adjuvant radiation remained free of recurrence within the radiation field during the first year of follow-up.¹⁴

Other factors that tip the scales toward radiation include deep invasion into the underlying connective tissue or skeletal muscle and the presence of perineural or vascular invasion. Conversely, if margins are wide and there is no deep invasion, skipping radiation may be reasonable.¹⁵ Given that many PDS patients are elderly and may have thin, fragile scalp tissue that heals poorly after radiation, the decision is a genuine tradeoff between local control and quality of life.

Systemic Therapy and Immunotherapy

For the small fraction of PDS patients who develop metastatic disease, treatment options are limited and borrowed from the broader soft-tissue sarcoma toolkit. Standard chemotherapy regimens use agents like adriamycin or ifosfamide, though evidence specific to PDS is scarce and largely drawn from case series rather than randomized trials.¹⁶

The high mutational burden of PDS has generated interest in immune checkpoint inhibitors, which work by releasing the brakes on the body’s immune system so it can attack cancer cells. There are published reports of complete responses to anti-PD-1 therapy in metastatic PDS, which is encouraging but still based on individual cases rather than large trials.¹⁷ The biological rationale is sound: tumors with many mutations tend to produce more abnormal proteins on their surface, making them more visible to the immune system. Whether checkpoint inhibitors will become a standard part of PDS treatment awaits larger prospective studies, but for patients with advanced disease, they represent one of the more promising avenues.

Where PDS Spreads

When PDS does metastasize, it follows a pattern familiar from other soft-tissue sarcomas. The lungs are the most common destination for distant spread, accounting for half of all distant metastases in a large nationwide Danish cohort. Locoregional spread to nearby skin or deep tissue was the next most frequent pattern, followed less commonly by bone, the parotid gland, and regional lymph nodes. A single case of brain metastasis was also recorded in that series.³ This is why chest imaging is prioritized during staging and follow-up: the lungs are both the most likely site and the most consequential to catch early.¹⁸

Immunosuppressed patients carry a disproportionate metastatic risk. As noted earlier, patients with underlying blood cancers were significantly more likely to develop distant organ metastases.² For patients who are immunosuppressed due to medication or disease, this translates to more aggressive initial treatment and closer surveillance after surgery.

Prognosis and Survival

Overall, PDS has a more favorable prognosis than many deeper soft-tissue sarcomas, though it is clearly more dangerous than its AFX counterpart. A Danish registry-based study found a five-year overall survival of about 67% for PDS, compared to 50% for subcutaneous undifferentiated pleomorphic sarcoma, confirming that the dermal-confined variant carries a meaningful survival advantage over deeper versions of the disease.¹⁹

Tumor grade has a strong influence on outcomes. An analysis of head and neck PDS found that five-year overall survival dropped in a stepwise fashion from 69% for grade I tumors to 42% for grade IV tumors. On adjusted analysis, patients with grade IV disease had roughly double the risk of death compared to those with grade I tumors.²⁰ It is worth noting that five-year survival figures for PDS partly reflect the advanced age of the patient population; many patients have competing causes of mortality from other conditions. Still, the grading data makes clear that not all PDS tumors behave the same, and tumor grade is one of the stronger predictors available for counseling patients about their individual outlook.

Follow-Up After Treatment

Because no PDS-specific surveillance guidelines exist, follow-up schedules are adapted from soft-tissue sarcoma protocols. One commonly used approach follows the National Comprehensive Cancer Network’s framework for soft-tissue sarcomas: visits every six months for the first three years after surgery, then annually.²¹ Other centers use a more intensive schedule of every three months for the first three years, then every six months for another two years, totaling five years of active surveillance with annual chest X-rays throughout.²²

The goals during follow-up are twofold: detecting local recurrence at the surgical site, and catching distant metastatic disease, primarily to the lungs. Physical examination of the scar and surrounding skin is the mainstay for detecting local recurrence, while chest imaging handles the metastatic surveillance. A UK audit across multiple dermatology departments recently endorsed following existing soft-tissue sarcoma guidelines until PDS-specific data matures enough to justify a tailored protocol.²³

The honest reality is that the evidence base for PDS management is still catching up with the diagnosis itself. The tumor was only separated from AFX as a distinct entity relatively recently, and most of the published literature consists of case series and retrospective cohort studies rather than prospective trials. For patients, this means that treatment plans may vary between institutions and that engaging with a multidisciplinary team, typically including a dermatologist, a surgeon with sarcoma experience, and a radiation oncologist, gives the best chance of a well-coordinated plan.

PDS Arising in Unusual Settings

While the vast majority of PDS cases occur on sun-damaged skin, the tumor occasionally appears in atypical locations or in the context of prior skin injury. One documented case involved PDS arising within a chronic burn scar on the forearm, a site without the heavy UV exposure profile typical of head and neck tumors. That case required MRI to assess dermal thickening and subcutaneous involvement, CT angiography to evaluate nearby blood vessels, and PET-CT for full staging before surgical planning could proceed.¹⁰ Cases like these serve as reminders that while UV damage is the dominant driver, chronic tissue injury or immunosuppression can occasionally produce PDS in unexpected places. Any rapidly growing nodule on chronically damaged skin, whether sun-exposed or not, warrants biopsy and evaluation by a dermatopathologist familiar with spindle-cell tumors.