Collision of actinic keratosis and dermatofibrosarcoma protuberans within a single lesion as a diagnostic pitfall: a case report

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Arch Craniofac Surg. 2025;26(6):261-265

Publication date (electronic) : 2025 December 20

doi : https://doi.org/10.7181/acfs.2025.0068

Yujin Ahn, Joon Ho Lee

Department of Plastic and Reconstructive Surgery, Dongguk University College of Medicine, Gyeongju, Korea

Correspondence: Joon Ho Lee, Department of Plastic and Reconstructive Surgery, Dongguk University College of Medicine, 123 Dongdae-ro, Gyeongju 38066, Korea, E-mail: urrussa@naver.com

Received 2025 October 20; Revised 2025 November 18; Accepted 2025 December 6.

Abstract

INTRODUCTION

Dermatofibrosarcoma protuberans (DFSP) is a rare, locally aggressive, cutaneous soft tissue sarcoma originating in the dermis [1]. It accounts for less than 0.1% of all malignancies and about 1% of soft tissue sarcomas [2]. DFSP most commonly arises on the trunk and extremities, but its occurrence on the face is extremely uncommon [3]. In contrast, actinic keratosis (AK) is the most common premalignant epidermal lesion worldwide and typically develops in chronically sun-exposed areas, such as the face [4]. There is no known association between DFSP and AK, and their pathogenesis differs fundamentally. Histologically, DFSP arises in the dermis, whereas AK is confined to the epidermis. Therefore, coexistence of these lesions at the same anatomical site is extremely rare. This manuscript was written to report a rare case of concurrent AK and DFSP arising within a single facial lesion, highlighting the diagnostic challenges when superficial biopsy only reveals the epidermal component. Through this case, we emphasize the need for repeat or deeper biopsies in atypical or non-healing lesions to avoid misdiagnosis and ensure appropriate management.

CASE REPORT

An 80-year-old man with underlying hypertension and diabetes mellitus presented to the dermatology department with the chief complaint of a non-healing ulcerative lesion on the right temple that had persisted for 6 months. A punch biopsy was performed at the center of the lesion, and the initial histopathological diagnosis was AK. The lesion appeared as a solitary erythematous ulcer measuring approximately 0.6×0.8 cm on the right temple (Fig. 1).

Fig. 1

Preoperative photograph of an 80-year-old man with a solitary erythematous ulcerative lesion (red circle) measuring 0.6×0.8 cm on the right temple.

The patient was referred to our department. On clinical examination, the lesion did not show the typical features of AK, and because the ulcer persisted without healing, another underlying lesion was suspected. A repeat biopsy revealed the coexistence of DFSP and bowenoid AK, with involvement of the deep and lateral resection margins.

The patient underwent Mohs micrographic surgery (MMS), a tissue-sparing technique involving stepwise excision of thin skin layers, each examined microscopically to confirm complete tumor removal with histologically clear margins while preserving healthy tissue. Following complete tumor clearance, reconstruction was performed using a parotid fascia-based bilobed fasciocutaneous flap. This flap was elevated based on the parotid fascia to provide robust blood supply, allowing effective coverage and tension-free closure of the surgical defect in the zygomatic and temporal regions. The bilobed flap was tailored to restore both functional and aesthetic aspects, achieving satisfactory contour and minimal donor site morbidity.

Histopathological examination of the excised specimen revealed distinct components consistent with AK: atypical keratinocytes confined to the basal and lower epidermis, characterized by nuclear hyperchromasia, crowding, and partial loss of polarity. Beneath the epidermis, storiform spindle cell proliferation was observed within the dermis, corresponding to DFSP. The two components were well demarcated with minimal histological overlap (Fig. 2). Immunohistochemistry revealed strong, diffuse CD34 positivity restricted to the dermal spindle cells, confirming the diagnosis of DFSP (Fig. 3A). In contrast, smooth muscle actin (SMA) staining was negative in these spindle cells (Fig. 3B), which is consistent with the typical immunophenotype of DFSP and aids in the exclusion of smooth muscle tumors.

Fig. 2

Photomicrograph of the specimen stained with hematoxylin and eosin (×100). Atypical keratinocytes confined to the epidermis consistent with actinic keratosis (red arrows), along with storiform spindle cell proliferation in the dermis characteristic of dermatofibrosarcoma protuberans (blue arrows).

Fig. 3

Photomicrographs of the specimen immunohistochemically stained for CD34 (A, ×200) and smooth muscle actin (SMA) (B, ×200). Diffuse and strong positivity for CD34 is observed in dermal spindle cells, supporting the diagnosis of dermatofibrosarcoma protuberans, while SMA staining is negative, consistent with the typical immunophenotype and aiding in the exclusion of smooth muscle tumors.

At the 2-month postoperative follow-up, the patient showed complete healing without recurrence or complications (Fig. 4). The patient remains under regular follow-up with clinical skin examinations every 6–12 months. If suspicious lesions occurred in the same area, a biopsy was performed to confirm recurrence.

Fig. 4

Postoperative photograph taken 2 months after Mohs micrographic surgery and bilobed flap reconstruction. Complete healing without recurrence or complications is observed.

DISCUSSION

DFSP is a rare cutaneous soft tissue sarcoma originating in the dermis. It primarily involves the dermis and subcutaneous tissue and accounts for less than 0.1% of all malignancies and approximately 1%–6% of all soft tissue sarcomas [1–3]. The most common site is the trunk, followed by the proximal extremities, head, neck, and, rarely, the hands and feet [3]. DFSP is typically present in adults aged 20–50 years with a slight female predominance [1]. Its pathogenesis is most notably associated with the translocation t(17;22)(q22;q13), resulting in the COL1A1-PDGFB fusion gene and subsequent activation of PDGFR-β signaling [1–3,5]. They are believed to originate from fibroblasts and dendritic cells. Trauma and skin lesions have also been reported previously [1,2].

Although no definite history of chronic irritation or trauma was reported by the patient, chronic minor mechanical irritation or persistent inflammation over the AK lesion may have contributed to dermal fibroblast transformation, facilitating the development of DFSP in the same site [1]. Chronic irritation has been suggested to promote neoplastic transformation through continuous damage and reparative processes [4]. Thus, the potential role of long-term irritation or trauma in the pathogenesis of these coexisting premalignant and malignant lesions should be acknowledged despite the absence of direct evidence in this case [2].

The diagnosis was established histopathologically. Hematoxylin and eosin staining revealed spindle cells in a storiform pattern infiltrating the dermis and subcutis, whereas immunohistochemical staining showed strong CD34 positivity. In contrast, SMA staining was negative or only focally positive, which helps exclude smooth muscle tumors in the differential diagnosis. Vimentin staining showed positivity, consistent with the mesenchymal origin of the tumor cells [1–3,5]. Molecular testing can be considered for ambiguous cases but is not routine. This addition clarifies the complementary role of SMA and vimentin immunostaining in confirming the diagnosis of DFSP and differentiating it from other spindle cell neoplasms [2].

MMS is currently recommended as the standard initial treatment for DFSP, owing to its ability to achieve complete excision while minimizing normal tissue loss [6]. Wide local excision with 2- to 3-cm margins is considered only when MMS is not available or feasible [7]. If the surgical resection margins are tumor-negative, adjuvant therapy is not recommended. Adjuvant radiotherapy or targeted therapy may be considered for unresectable cases. Both MMS and wide local excision showed lower recurrence rates when complete tumor clearance was achieved [8]. MMS with precise margin control is particularly effective for minimizing local recurrence. Clinical examination every 6–12 months postoperatively, followed by annual assessments thereafter, is recommended to facilitate early detection of recurrence AK is a premalignant lesion caused by chronic ultraviolet radiation exposure that commonly affects sun-exposed skin. Clinically, AK presents as a rough, scaly plaque and carries the risk of progression to squamous cell carcinoma. Histologically, AK shows atypical keratinocytes in the basal layer of the epidermis and features, such as nuclear atypia, hyperchromasia, pleomorphism, parakeratosis, and solar elastosis [4,9,10].

Treatment depends on the extent of disease. Cryotherapy is the first-line treatment for localized lesions, whereas topical agents such as 5-fluorouracil, imiquimod, tirbanibulin, or photodynamic therapy are preferred for field cancerization. Surgical excision is generally performed for suspected invasive squamous cell carcinoma [4,9,10].

Accurate diagnosis is crucial as treatment strategies for DFSP and AK differ significantly. Although histopathological examination is essential for diagnosing both entities, their location in different skin layers can lead to diagnostic pitfalls when they coexist within the same lesion. A superficial biopsy that only samples the epidermis may identify AK alone, while missing underlying DFSP. Thus, in cases with atypical clinical features or non-healing lesions, repeat or deeper biopsy should be considered to avoid misdiagnosis and enable timely and appropriate treatment. In this case, the initial biopsy revealed only AK, which commonly requires medical rather than surgical management. However, because the clinical features were atypical and the ulcer had persisted, a deeper and broader biopsy was performed, which revealed DFSP and AK.

An initial diagnostic discrepancy often occurs due to the distinct cutaneous layers involved. DFSP extends into the full dermis and subcutis, requiring a biopsy depth of at least 4–6 mm for accurate diagnosis, whereas AK is limited to more superficial layers. Furthermore, biopsy site selection is important; tumor margin sampling improves the accuracy of DFSP, whereas center sampling is typical for AK. A punch biopsy, which is frequently used because of its simplicity, may miss deep lesions. Therefore, for atypical lesions or persistent ulcers, repeat or deeper biopsies must be considered to avoid misdiagnosis and ensure appropriate management.

In conclusion, the patient recovered completely after surgery. This case highlights the extremely rare coexistence of AK and DFSP on the face and underscores the importance of a precise diagnosis and clinicopathological correlation. Superficial biopsy alone can obscure the underlying dermal malignancy, ultimately delaying proper treatment. Clinicians should maintain a high index of suspicion for atypical or non-healing ulcerative lesions and pursue repeat biopsies with comprehensive evaluation when warranted. Complete surgical excision with histologically clear margins is the cornerstone of treatment and prognosis.

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