Desmoplastic trichoepithelioma with pseudocarcinomatous hyperplasia: a report of three cases

We report three cases of desmoplastic trichoepithelioma (DTE) with overlying pseudocarcinomatous hyperplasia. All three cases developed on the face of patients in their second decade. In spite of their young age, a diagnosis of squamous cell carcinoma was considered for each case, given the unusual juxtaposition of these two well‐known simulators of malignancy. Awareness of this potential association may avert a misdiagnosis of malignancy.     

Desmoplastic sebaceoma arising from nevus sebaceus: a new variant

Nevus sebaceus is known to have the potential to develop into various secondary tumors. We observed a sebaceoma arising from a nevus sebaceus excised from the left cheek of a 51‐year‐old woman. This sebaceoma showed desmoplastic change similar to that observed in desmoplastic trichoepithelioma and desmoplastic trichilemmoma. This heretofore undescribed desmoplastic variant of sebaceoma should not be mistaken for invasive sebaceous carcinoma.     

Desmoplastic melanoma: an updated immunohistochemical analysis of 40 cases with a proposal for an additional panel of stains for diagnosis

Desmoplastic melanoma (DM) is histologically characterized by a proliferation of spindle melanocytes dispersed in a collagenous stroma that can be mistaken for a variety of neoplasms. The purpose of this study was to analyze 40 cases of DM with a comprehensive panel of immunohistochemical markers (KBA.62, p16, Ezrin, WT‐1, MITF‐1, SOX‐10, CD117, SOX‐2, nestin, PNL2, p75, MART‐1, gp100 and S100p) to obtain a more complete understanding of the potential use of these antibodies in the diagnosis of DM. We found that all cases of DM expressed p16, WT‐1, SOX‐10, nestin and S100p and 95% of cases expressed p75. There was variable expression with Ezrin, SOX‐2, KBA.62, MART‐1 and HMB‐45. Most DMs did not express MITF‐1, PNL2 and CD117. Conditions that may enter in the histologic differential diagnosis of DM, including dermal scars, fibromatosis and dermatofibromas were also studied. Nearly all control cases also stained positive for p16 but were negative for WT1, SOX10, nestin, p75 and S‐100p, as well as for most of the other markers tested. We conclude that a panel of S‐100p, WT1, SOX10, p75 and nestin may constitute the optimal panel with the most sensitive and specific combination of immunostain available for the diagnosis of DM.     

Desmoplastic melanoma may mimic a cutaneous peripheral nerve sheath tumor: Report of 3 challenging cases

Desmoplastic melanoma (DM) and cutaneous malignant peripheral nerve sheath tumors (MPNST) reveal histological and immunohistochemical similarities, including S100 positivity and negative staining for conventional melanocytic markers. We present 3 cases of cutaneous S100‐positive spindle cell tumors in elderly patients, in which first findings led to initial misdiagnoses as cutaneous MPNST and benign peripheral sheath nerve tumor (neurofibroma). The identification of adjacent atypical melanocytic hyperplasia in the overlying skin along with tumor cell proliferation, also in the superficial dermis, the neurotropic component and the absence of any relationship between the tumor and a major nerve, pre‐existing neural benign tumor or the existence of stigmata suggestive of neurofibromatosis raised consideration of a DM. Careful attention should be paid to the presence of a firm dermal nodule and atypical scar lesions especially in sun‐exposed areas (mainly head and neck region) in elderly patients associated with S100‐positive spindle cell proliferation, solar elastosis and adjacent atypical melanocytic proliferation. In such cases, the possibility of a DM should be excluded with caution, especially if the tumor reveals a paucicellular morphology resembling various non‐melanocytic neoplasms including malignant or benign peripheral sheath nerve tumors.     

Subcutaneous desmoplastic small round-cell tumor: An unusual primary location expanding the differential of superficial round-cell tumors

Desmoplastic small round-cell tumor (DSRCT) is a rare, aggressive malignant tumor, which in the great majority of cases arises at abdominal-pelvic sites. Nevertheless, rare cases of primary extra-abdominal tumors have been reported. In challenging cases, its molecular hallmark, the EWSR1-WT1 reciprocal translocation, can be exploited diagnostically by various molecular techniques. Herein, we report an extremely rare case of primary subcutaneous DSRCT in an effort to raise awareness among our dermatopathology colleagues by expanding the differential of superficial round-cell tumors.     

Superficial dermal melanocytosis of the elderly: An exceptional occurrence?

The development of flat pigmented lesions on chronically sun-damaged (CSD) skin of the face may represent the clinical manifestation of a wide variety of hyperplastic/neoplastic melanocytic proliferations. We report the exceptional case of an acquired pigmented patch occurring on CSD skin, histopathologically characterized by diffuse hyperplasia of dendritic/spindled melanocytes in the superficial dermis within a widened band of actinic elastosis. This lesion was associated with a small focus of early invasive lentigo maligna melanoma (LMM). We show the melanocytic nature of the population of dermal pigmented cells by means of single and double immunohistochemical staining for melanocytic and histiocytic markers. The biologic significance of the focus of LMM within the hyperpigmented lesion (whether random collision phenomenon or causally related occurrence), as well as the pathogenesis of the whole dermal lesion are difficult to elucidate. Our case emphasizes the need for a better understanding of the pathophysiology of so-called dermal melanocytes.