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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.

Background: Soft tissue giant cell tumor (GCT-ST) of low malignant potential is an uncommon neoplasm, considered the soft tissue counterpart of giant cell tumor of bone. GCT-ST mainly affects young to middle-age adults and presents as a painless growing mass mainly located in the lower extremities and trunk. Histologically, this tumor is characterized by a mixture of uniformly scattered osteoclast-like multinucleated giant cells intimately admixed with short fascicles of spindled cells. Complete excision with negative surgical margins is associated with a benign clinical course in most cases. Methods: The authors report the clinicopathological and immunohistochemical features of an unusual GCT-ST of 46 years duration previously histologically misdiagnosed as Kaposi's sarcoma. Results: Histologically, the tumor was characterized by a multinodular growth pattern with osteoclast-like multinucleated giant cells admixed with spindle cells partially arranged in a storiform pattern, fibrosis and foci of haemorrhage and mature bone. Immunohistochemistry revealed CD68 reactivity of the multinucleated giant cells. Conclusion: GCT-ST is a rare neoplasm characterized by benign clinical course if excised adequately, as shown by our case of exceptionally long duration. Emphasis is placed on the importance of differential diagnosis with other giant cell-rich soft tissue neoplasms because clinical behaviour, prognosis and treatment significantly differ.

Various cytogenetic and molecular findings indicate 1p36 loss as a consistent change in sporadic and inherited chordoma, a rare embryogenetic neoplasm arising from notochord remnants. We studied 27 sporadic chordomas by means of loss of heterozygosity (LOH) of 31 microsatellites localized to the 1p36.32-36.11 region, and restricted the minimal LOH interval shared by 85% of the tumours to 1p36.13. We also used RT-PCR analysis to investigate the role of the candidate genes CASP9, EPH2A, PAX7, DAN and DVL1, which were selected on the basis of the physical mapping of the LOH region and their plausible oncosuppressor function. RT-PCR analysis showed the presence of DAN and PAX7 transcript fragments of the expected size in all of 8 chordoma samples, whereas the CASP9-specific fragment was observed in only 3 and EPH2A was absent in one. Smaller than expected DVL1 transcripts were found in 4 tumours as well as in their normal counterpart (nucleus pulposus), which also showed a typically sized transcript. Sequencing revealed the skipping of 3 exons in the smallest DVL1 fragment, thus leading to a frameshift and predicting a truncated DVL1 gene product. Our study of the largest cohort of chordoma patients recruited so far indicates a common molecular lesion at 1p36.13, and suggests that the CASP9, EPH2A and DVL1 genes may play an onco-suppressing role and be involved in the development of chordoma.

A slowly growing malignant tumor of the nail unit in a 74-year-old female is reported. At light microscopy, the tumor was composed of small keratinous cysts with abrupt central keratinization, and of solid nests and strands of atypical keratinocytes filling the dermis and penetrating the phalangeal bone. In our view, this can be regarded as the malignant analog of the keratin cysts arising from the nail bed epithelium, as first reported by Samman in 1959. Since, according to several authors, the nail bed epithelium is comparable to the outer root sheath of the follicle and since the reported tumor showed some analogies with malignant proliferative trichilemmal cyst, it is suggested that this new entity be designated as malignant proliferating onycholemmal cyst.