Unmasking the Hidden Threat: Residual Melanoma Mimicking Scar Tissue

Summary: Background: Melanoma's variable morphologies, including desmoplastic and spindle-cell features, pose a significant diagnostic challenge, particularly when these mimic benign scar tissue. Accurate diagnosis relies on careful comparison of the initial biopsy and excision specimens, as overlooking subtle clues can lead to serious clinical consequences. Case Presentation: An 82-year-old male with a history of T1b melanoma, NOS, nonulcerated, of the left scalp (Breslow thickness 1.0 mm), previously biopsied, underwent excision. The excision specimen predominantly showed desmoplastic spindle cells at the scar site, with rare atypical cells displaying large, irregular nuclei and cherry-red nucleoli, raising suspicion for residual melanoma. Immunohistochemical staining (SOX10, Melan-A) confirmed residual melanoma, highlighting the atypical cells and focally staining the spindle cells (Breslow thickness 0.3 mm). Retrospective review of the original biopsy revealed spindled atypical melanocytes extending into desmoplastic stroma, underscoring a consistent but initially underappreciated morphologic pattern. Conclusion: This case illustrates the critical importance of recognizing subtle diagnostic clues, such as rare atypical cells, which prompted further evaluation in this instance. The spindle cells were initially misinterpreted as scar tissue, leading to a potential diagnostic oversight. These findings emphasize the necessity of biopsy-excision correlation and vigilant evaluation to avoid misdiagnosis in melanoma cases.