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Context.-Selected cutaneous neoplasms share features with benign counterparts or have subtle morphologic features that could be overlooked by the pathologist.
Objective.-To present clues to the diagnosis of potentially deceptive malignancies, including desmoplastic malignant melanoma, nevoid malignant melanoma, subcutaneous lymphoma, metastatic breast carcinoma, and epithelioid sarcoma.
Data Sources.-Published literature and personal experience.
Conclusions.-Knowledge of commonly misdiagnosed cutaneous neoplasms will help the general surgical pathologist avoid these potential pitfalls in neoplastic dermatopathology.
(Arch Pathol Lab Med. 2007;131:434-439)
Diagnostically difficult cutaneous neoplasms are a consistent problem in dermatopathology. They are typically examined closely and often shared with colleagues in order to arrive at a consensus. However, some of the most unsettling lesions are those malignant tumors that are so innocuous-looking histopathologically that they escape special scrutiny. In this review, we consider selected cases that closely simulate benign lesions. By virtue of their bland features, such "wolves in sheep's clothing" may not be recognized when examined at scanning magnification.
DESMOPLASTIC MALIGNANT MELANOMA
Desmoplastic malignant melanoma (DMM) is an uncommon variant that may have banal features both clinically and histopathologically.1 In a recent review of malpractice claims centering on melanoma, unrecognized DMM accounted for a disproportionate number of diagnostic errors.2 The typical clinical presentation is that of a firm papule, nodule, or plaque on sun-exposed areas of the head and neck in an elderly patient.3-5 However, other anatomic sites may be involved, including oral or anogenital mucosa.6-8 In some cases, DMM may arise in a preexisting malignant melanoma in situ of the lentiginous (so-called lentigo maligna) type. When DMM arises in malignant melanoma in situ, the pigmentation of the junctional component may provide a clinical clue as to the tumor's melanocytic lineage. On the other hand, when DMM occurs without an associated junctional melanocytic proliferation, the lesion appears nonpigmented and does not resemble the usual clinical image of melanoma. Instead, the clinical features may falsely suggest a cicatrix, dermatofibroma, nevus, basal cell carcinoma, or cyst.3,9
In DMM, histopathologic examination reveals a dermal proliferation of spindle cells associated with a variable fibrotic stromal response (Figure 1). The tumor cells may be dispersed individually and haphazardly between the collagen bundles or may be grouped in long fascicles.5,10 A whorled or storiform pattern is seen in some cases. Deep dermal involvement and...