The Great Mimicker: A Case Highlighting Amelanotic Spitzoid Melanoma

A 34-year-old woman presented to the clinic with a 7-month history of a solitary growth on her right upper leg. The lesion had begun as a small pink bump and had grown slowly over the past 7 months (Figure 1 and 2). She denied any associated bleeding or symptoms. She also denied any history of physical trauma or any arthropod bite to the area. She also denied having any other skin lesions. Her past medical history included migraines; however, there was no personal or family history of skin cancer. 

skin cancer

On physical exam, the patient was a well-nourished, healthy, 34-year-old woman with an 8-mm pink, slightly pedunculated, papule on her right upper outer thigh. No other similar lesions were noted on physical exam. On dermoscopy, small cerebriform pink sulci were noted within the papule, without any pigment network or atypical appearing globules or crystalline structures. No ulceration was noted and the surrounding skin was unremarkable. 

skin cancerDue to the lesion growing in size and the patient being concerned about the lesion, the lesion was biopsied with a deep shave technique and sent for histologic examination. Our differential diagnoses included an irritated compound nevus, acrochordon, neuroma, pyogenic granuloma, neurofibroma, or a connective tissue nevus. 
Histologic exam of the lesion showed a severely atypical compound Spitzoidmelanocytic proliferation best regarded as a malignant melanoma with dermal invasion to a thickness of 1.5 mm. The lesion was not ulcerated and had a mitotic count of 2 mitotic figures/mm2. No lymphovascular invasion or microsatellitosis was identified (Figures 3 and 4). 
The diagnosis of an atypical Spitzoid melanoma was made due to the severe degree of cytologic atypia, the lack of maturation of the dermal component, the presence of deep dermal mitotic figures, the loss of p16 immunopositivity, and the retention of HMB-45 immunopositivity in the dermal component. 
Based on the clinical and histopathologic findings, a diagnosis of an amelanotic Spitzoid malignant melanoma was made and the patient was referred to oncologic surgery for wide local excision and sentinel lymph node biopsies in her right groin was performed. The sentinel lymph nodes were negative and there was no residual melanoma at the primary site.  

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