Keloids are benign fibroproliferative scars characterized by excessive collagen deposition and persistent fibroblast activity, often extending beyond the boundaries of the original injury. While typically regarded as non-neoplastic, emerging evidence suggests that keloid tissue may, in rare cases, undergo malignant transformation [1]. The mechanisms underlying this transformation remain unclear, although chronic inflammation, repeated mechanical trauma, and tissue‑microenvironmental changes are implicated.

Sarcomatoid squamous cell carcinoma (SSCC) is a rare and aggressive histologic variant of squamous cell carcinoma (SCC) that displays both epithelial and mesenchymal (spindle cell) differentiation. It is most commonly found in mucosal sites of the head and neck, and primary cutaneous SSCC is exceptionally rare. SSCC poses significant diagnostic and therapeutic challenges due to its histologic overlap with other spindle cell neoplasms and its high metastatic potential.

To our knowledge, this is the first reported case of SSCC arising within a keloid scar. This case underscores the rare but clinically important potential for malignant transformation in keloid tissue, particularly following repeated mechanical trauma such as acupuncture.

A 78‑year‑old woman presented with a progressively enlarging mass on the right auricle. Her history included hypertension, dyslipidemia, chronic kidney disease, and polycythemia vera– related myelofibrosis treated with ruxolitinib. Several years prior to presentation, she had undergone acupuncture on the right auricle as part of treatment for knee pain. She subsequently developed a hypertrophic scar and scab at the site, which she attributed to a benign process. One year prior to presentation to our clinic, the lesion exhibited rapid growth and morphological changes, prompting further evaluation.

On physical examination, a 3×3 cm exophytic, ulcerated, and friable mass was observed on the superior aspect of the right auricular helix (Fig. 1). The lesion bled spontaneously on palpation and was mildly tender. A punch biopsy performed in the outpatient clinic revealed a malignant mesenchymal tumor with spindle cell proliferation, pleomorphic nuclei, and frequent mitoses. Immunohistochemical analysis demonstrated strong vimentin positivity, while staining for smooth muscle actin (SMA), S‑100 protein, cluster of differentiation 34 (CD34), cytokeratin (CK) AE1/AE3, and p63 was negative. Magnetic resonance imaging revealed a heterogeneously enhancing soft tissue mass abutting the auricular cartilage. Computed tomography of the neck and positron emission tomography showed no evidence of regional or distant metastases.

The patient underwent wide local excision under general anesthesia with a 4 mm margin. Given the magnetic resonance imaging findings, a portion of the auricular cartilage was excised along with the mass, and the defect was closed primarily. As imaging did not reveal suspicious lymphadenopathy, sentinel lymph node biopsy was omitted. Histologic examination showed a malignant squamous epithelial component superficially and a spindle‑shaped component infiltrating the underlying stroma (Fig. 2A). The stromal sarcomatoid component exhibited marked nuclear pleomorphism, bizarre tumor giant cells, and frequent mitoses (Fig. 2B). Immunohistochemical stains were positive for CK (Fig. 3A), vimentin (Fig. 3B), SMA, and desmin; stains for CD34, S‑100 protein, human melanoma black‑45, and myogenin were negative, confirming both epithelial and mesenchymal differentiation. Although the tumor was initially suspected to have arisen in a preexisting keloid scar based on clinical history and gross findings, final diagnosis by the pathology department confirmed that the tumor had indeed originated within keloidal tissue. Surgical margins were free of tumor, with no evidence of lymphovascular or perineural invasion, and the auricular cartilage was uninvolved. The postoperative course was uneventful, with suture removal on postoperative day 14. At 6 months follow‑up, there was no evidence of local recurrence or distant metastasis (Fig. 4).

SSCC is an uncommon histologic subtype of SCC characterized by a biphasic pattern with both spindle‑shaped stromal and epithelial components [2]. Although the exact pathogenesis of SSCC is not fully understood, the leading hypothesis posits that conventional SCC cells undergo dedifferentiation, acquiring mesenchymal traits—a process supported by molecular evidence of shared clonal origins and specific genetic alterations [3].

Clinically, SSCC presents as a protruding, ulcerated lesion. Histology shows dysplastic squamous epithelium merging into a malignant spindle cell component. Immunohistochemically, SSCC expresses epithelial markers (AE1/AE3, p63, EMA) alongside vimentin, reflecting mesenchymal differentiation [4]. SSCC diagnosis can be challenging due to histologic overlap with other spindle cell tumors, so accurate diagnosis depends on identifying epithelial features through histology and immunohistochemistry to distinguish SSCC from true sarcomas or other spindle cell neoplasms. Debate continues over its classification as “sarcomatoid SCC” versus “spindle cell carcinoma” [5]. Given its aggressive course and poor prognosis, timely and accurate diagnosis is critical.

SSCC accounts for approximately 3% of head and neck SCCs, most often affecting the larynx but also reported in the oral tongue, gingiva, nasal cavity, and hypopharynx [6,7]. Primary cutaneous SSCC is exceptionally rare and exhibits more aggressive behavior and poorer outcomes than conventional SCC. A review of 187 laryngeal SSCC cases reported a 5‑year survival of 64.4% [8], whereas SSCC in various mucosal sites demonstrated a 5‑year survival of 6.7% [9]. Distant metastases frequently involve the lungs, liver, and kidneys, and satellite or in‑transit metastases have been described. Some patients experience rapid progression despite surgery and systemic chemotherapy [10].

Keloids are pathological scars arising from abnormal wound healing, characterized by excessive fibroblast activity and colla-gen deposition. Unlike typical scars, keloids extend beyond the initial wound margins and are often raised, irregular, and symptomatic, with pruritus or pain. Risk factors include infection, wound tension, foreign bodies, and repeated trauma, with higher prevalence in individuals with darker skin phototypes. Histologically, keloids comprise dense, disorganized collagen bundles, fewer fibroblasts, and low vascularity, creating a hypoxic microenvironment [1].

Although keloids are benign, rare cases of malignancy—such as SCC [1] and basal cell carcinoma [11]—have arisen within keloid tissue. The mechanisms underlying malignant transformation of keloids are not fully elucidated. Keloid tissue is characterized by chronic inflammation and hypoxia, with elevated pro-inflammatory mediators. Key fibrogenic cytokines, particularly transforming growth factor (TGF)-β1, stimulate fibroblast proliferation and collagen synthesis, contributing both to fibrosis and tumorigenesis. Dysregulation of the TGF-β/Smad pathway has been implicated in scar formation and skin cancer development. Other inflammatory regulators—including nuclear factor kappa-light-chain-enhancer of activated B cells, signal transducer and activator of transcription 3, hypoxia-inducible factor 1-alpha—also promote cancer progression. Additionally, microRNAs such as the miR-29 family have roles in keloid pathophysiology and carcinogenesis, influencing the tumor microenvironment [12].

An epidemiological study reported a 1.73‑fold increase in skin cancer incidence among individuals with keloids, independent of sex [12]. Conversely, in breast cancer patients, elevated growth factors—such as TGF‑β, vascular endothelial growth factor, and platelet‑derived growth factor—may exacerbate preexisting keloids [13].

Acupuncture, commonly used to relieve pain, is generally considered safe [14]. However, complications, such as lymphedema after breast cancer-related acupuncture [15] and suspected cutaneous metastases triggered by acupuncture‑related trauma, have been reported [16].

This case illustrates an exceptionally rare instance of SSCC developing within a preexisting keloid scar, a phenomenon that has been scarcely documented in the literature. Although SCC arising in keloidal tissue has been sporadically reported [1,11], routine histologic evaluation of excised keloids seldom reveals malignancy, one study of over 500 specimens found no cases of cancer [17]. This case is particularly significant because it documents SSCC arising within a keloid scar—a combination not previously reported. The lesion had remained stable for years but showed a sudden increase in size and altered morphology, prompting further investigation. This underscores the need for careful monitoring of keloids, especially those exhibiting atypical growth or changes in appearance.

In our case, SSCC developed in a longstanding keloid subjected to repeated acupuncture, suggesting that chronic microtrauma and mechanical irritation may promote carcinogenesis in fibrotic tissue. Chronic irritation can impair local immune surveillance and prolong exposure to carcinogenic factors, fostering a tumor‑permissive microenvironment [1,12]. Moreover, keloids are relatively uncommon in elderly individuals, and the occurrence of a keloid in this 78-year-old patient is considered an infrequent finding. Keloids tend to occur more frequently in individuals between the ages of 10 and 30, and are rarely seen at the extremes of age, such as infancy or old age. This age-related distribution may be attributed to the higher incidence of trauma in younger populations and the greater skin elasticity observed in younger individuals compared to the elderly [18]. The development of SSCC within such a lesion further highlights the rarity and clinical relevance of this case

The mainstay of SSCC treatment is wide local excision with negative margins. While adjuvant chemotherapy or radiotherapy may be considered in select high‑risk cases, their effectiveness remains uncertain. The auricle, in particular, is a high‑risk location for cutaneous SCC, with a metastasis rate of approximately 15.5%, especially when cartilage is involved [19]. Adjuvant radiotherapy may reduce recurrence in such cases. In the present case, the tumor was excised with a 4 mm margin; histopathology showed no cartilage invasion or lymphovascular/perineural spread, and imaging ruled out regional lymph node metastasis. While adjuvant radiotherapy was considered due to the auricle’s known high-risk status for metastasis [19], and given that a 1 cm safety margin is generally recommended for SSCC due to its aggressive nature [2], the patient opted against further treatment. At 6-month follow-up, no recurrence was noted, suggesting that surgery alone may be sufficient in carefully selected cases.

Ultimately, this case reinforces the importance of recognizing atypical features in longstanding keloid scars and considering malignant transformation. Further studies are needed to elucidate the pathophysiology of this process and to identify risk factors that could guide clinical decision‑making.