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Ultrastructural and immunohistochemical characterization of the so-called giant multinucleate cells in cutaneous collagenomas Aims: This study was undertaken to compare the histopathological, immunohistochemical and ultrastructural features of the so-called giant multinucleatecells in cutaneous collagenomas: giant-cell collagenoma and solitary sclerotic fibroma. Methods and results: We studied four collagenomas: one giant-cell collagenoma and three solitary sclerotic fibromas. All the cases showed an indolent clinical presentation and were histologically constituted by a well-demarcated dome-shaped proliferation of coarse collagen bundles with a varying number of interspersed giant multinucleate cells and stellate mononuclear cells. The immunohistochemical study on paraffin sections revealed that neoplastic cells in both collagenomas were vimentin and CD34-positive, whereas FXIIIa was only expressed in solitary sclerotic fibromas. In regard to the so-called giant multinucleate cells, we have ultrastructurally found that these cells were ‘real’ multinucleate cells in giant-cell collagenoma, whereas in solitary sclerotic fibromas they consisted of closely packed aggregates of individual stellate mononuclear cells. Moreover, perinuclear cisternae focally containing finely textured material of moderate density were unexpectedly found in giant cells of giant-cell collagenoma, a finding which was not observed in solitary sclerotic fibromas. Additionally, a characteristic cell–cell interaction between tumour cells and mast cells was encountered in all collagenomas. Conclusions: This study supports a distinctive immunohistochemical and overall ultrastructural profile of giantmultinucleate cells in giant-cell collagenoma and solitary sclerotic fibroma, which suggests a different pattern of differentiation for these two related cutaneouslesions.

Psammomatous malignant melanoma arising in an intradermal naevus Aims: A wide variety of differentiation patterns may be found in malignant melanoma. Schwannian features are unusual, and mostly present in the desmoplastic variant. We report the first description of psammoma bodies in malignant melanoma. Methods and results: A malignant melanoma arose in an intradermal naevus of the scalp in a 51-year-old woman, displaying focal neural-like features in the form of rosette-like pseudo-meissnerian alveolar nests, as well as numerous psammoma bodies grouped in a few areas. Tumour cell immunostaining for S100, HMB45, NKI-C3, and vimentin was detected. In addition, both malignant and benign melanocytic cells showed widespread MART-1 immunoreactivity. Differential diagnosis with psammomatous melanotic schwannoma, a feature of Carney’s complex, is particularly emphasized, since dermal variants of this nerve sheath neoplasm have been described. In addition, its potential relationship with cutaneous malignant melanotic neurocristic tumour is discussed. Conclusions: This is, to our knowledge, the first reported case of cutaneous malignant melanoma with psammoma bodies.

Cutaneous sclerosing Pacinian-like perineurioma Aims: The term perineurioma has been used to designate a variety of clinically and histologically different proliferations of perineurial cells based on immunohistochemical and/or ultrastructural characterization. There are two different groups of neoplasms derived from perineurial cells: extraneural or soft tissue perineuriomas, and intraneural perineuriomas. Recently, a sclerosing variant of cutaneous perineurioma has been described. Methods and results: We report a case of a cutaneous form of perineurioma, combining features of the intraneural and sclerosing varieties, as well as showing a Pacinian pattern of growth. In order to assess the neoplastic nature of the lesion, we performed fluorescence in-situ hybridization (FISH) analysis using a probe which maps to the chromosome band 22q11 and 22q13, allowing us to show deletion or loss of one chromosome 22 in the tumour cells. Conclusions: This case may be considered a new variant of perineurioma with Pacinian-like features, for which we propose the designation ‘sclerosing Pacinian-like perineurioma’.

Aims: Malignant proliferating trichilemmal tumours (MPTT) are rare neoplasms capable of tissue invasion and metastasis, the diagnosis of which is based essentially on histological features. In difficult cases, however, evaluation of additional parameters may be needed to diagnose malignancy. Methods and results We report three cases of MPTT in which, in addition to the histological features, we have determined the DNA ploidy, nuclear area and proliferative fraction. CD34 immunoreactivity has also been tested. Two cases were aneuploid, and one diploid with increased proliferating index. PCNA immunostaining labelled 40% and 80% of tumour cells in aneuploid tumours and 30% of the diploid neoplasm. In all cases, nuclear area was consistent with large pleomorphic tumour cells. No CD34 immunostaining was detected. Conclusions Aneuploidy is common in MPTT, particularly in tumours with a high proliferative fraction. Loss of CD34 immunoreactivity is an additional feature of potential, though limited, value. Therefore, evaluation of the DNA content, proliferation markers and CD34 immunostaining may be helpful in the diagnosis of MPTT.

Aims: Erythrophagocytosis is a characteristic feature of tumour cells in malignant histiocytosis, some leukaemias, lymphomas, and also reactive histiocytes in the haemophagocytic syndrome associated with a variety of infections and neoplasms. It has also been found exceptionally in metastatic malignant epithelial cells in bone marrow and lymph nodes. We present two cases, a cutaneous malignant melanoma and an acantholytic squamous cell carcinoma, in which erythrophagocytosis by tumour cells was demonstrable by both light and electron microscopy. Methods and results: The melanocytic and squamous nature of these cells was supported by the immunohistochemical detection of HMB45, S100, and NKI-C3 in the former, and cytokeratin and EMA in the latter, and at ultrastructural level by the presence of melanosomes and tonofilaments, respectively. Conclusions: This is, to our knowledge, the first documented report of erythrophagocytic tumour cells in human melanomas and primary carcinomas. Biological considerations apart, this unusual feature can prove to be of value to avoid a misdiagnosis of a variety of haematopoietic malignancies.

Aims: To analyse the presence of collagen type I alpha 1–platelet-derived growth factor beta (COL1A1–PDGFB) transcripts in 20 cases of dermatofibrosarcoma protuberans (DFSP) and to assess the relationship between COL1A1 breakpoints and clinical and histopathological variables. Methods and results: Multiplex reverse transcriptase-polymerase chain reaction was carried out using frozen tissue. Our series contained 14 men and six women. Histologically, most cases were of conventional type (n = 9), followed by fibrosarcoma (n = 4), Bednar tumour (n = 2), sclerosing (n = 2), myoid (n = 1) and atrophic (n = 1) DFSP, and giant cell fibroblastoma (n = 1). Immunohistochemistry revealed CD34 expression in 90% of cases. COL1A1–PDGFB fusion transcripts were present in 89% of cases (exons 18, 19, 20, 25, 26, 31, 33/34, 39, 40, 46, 47 and 48 of COL1A1 with exon 2 of PDGFB). There was no recurrence of DFSP in any of the 19 patients treated by Mohs surgery. A partial response was obtained in the two patients treated with imatinib. Conclusions: The COL1A1–PDGFB fusion was present in all histological subtypes of DFSP, but not all cases expressed the fusion transcript. No association was observed between different COL1A1 breakpoints and clinicopathological parameters. Imatinib mesylate can be useful in locally advanced tumours and metastases.

Aims: To evaluate the clinicopathological and immunohistochemical characteristics of Merkel cell carcinoma (MCC) in an attempt to find new, potentially significant, prognostic markers. Methods and results: Clinical data and follow-up, histopathological features (pattern, cell size, thickness, mitoses, vascular invasion, lymphocytic infiltration) and immunohistochemical detection [CK20, thyroid transcription factor (TTF-1), chromogranin A, synaptophysin, p53, Ki67, Fli-1, CD99, c-Kit] were evaluated in 20 cases of MCC. Fli-1 and CD99 were detected in 90% and 55% of cases, respectively. Tumour size > 30 mm, stage II, ‘absent’ lymphocytic infiltration, and the presence of > 50% of Ki67+ tumour cells, were found to be prognostic indicators of disease-free interval (DFI), but only ‘absent’ lymphocytic infiltration constituted an independent prognostic factor of DFI after multivariate analysis. For overall survival, the same variables, together with local recurrence and lymph node involvement, had prognostic significance, with only local recurrence as an independent prognostic factor after multivariate analysis. Conclusions: Absence of lymphocytic infiltration and Ki67 immunoreactivity in more than 50% of tumour cells should be evaluated in conjunction with other well-known prognostic markers in MCC. Furthermore, recognizing that Fli-1 and CD99 expression is commonly found in MCC by immunohistochemistry may avoid misinterpretation in the differential diagnosis of MCC with other small round cell tumours.

This study was undertaken to compare the histopathological, immunohistochemical and ultrastructural features of the so-called giant multi nucleate cells in cutaneous collagenomas: giant-cell collagenoma and solitary sclerotic fibroma.We studied four collagenomas: one giant-cell collagenoma and three solitary sclerotic fibromas. All the cases showed an indolent clinical presentation and were histologically constituted by a well-demarcated dome-shaped proliferation of coarse collagen bundles with a varying number of interspersed giant multinucleate cells and stellate mononuclear cells. The immunohistochemical study on paraffin sections revealed that neoplastic cells in both collagenomas were vimentin and CD34-positive, whereas FXIIIa was only expressed in solitary sclerotic fibromas. In regard to the so-called giant multinucleate cells, we have ultrastructurally found that these cells were 'real' multinucleate cells in giant-cell collagenoma, whereas in solitary sclerotic fibromas they consisted of closely packed aggregates of individual stellate mononuclear cells. Moreover, perinuclear cisternae focally containing finely textured material of moderate density were unexpectedly found in giant cells of giant-cell collagenoma, a finding which was not observed in solitary sclerotic fibromas. Additionally, a characteristic cell-cell interaction between tumour cells and mast cells was encountered in all collagenomas.This study supports a distinctive immunohistochemical and overall ultrastructural profile of giant multinucleate cells in giant-cell collagenoma and solitary sclerotic fibroma, which suggests a different pattern of differentiation for these two related cutaneous lesions.

A wide variety of differentiation patterns may be found in malignant melanoma. Schwannian features are unusual, and mostly present in the desmoplastic variant. We report the first description of psammoma bodies in malignant melanoma.A malignant melanoma arose in an intradermal naevus of the scalp in a 51-year-old woman, displaying focal neural-like features in the form of rosette-like pseudo-meissnerian alveolar nests, as well as numerous psammoma bodies grouped in a few areas. Tumour cell immunostaining for S100, HMB45, NKI-C3, and vimentin was detected. In addition, both malignant and benign melanocytic cells showed widespread MART-1 immunoreactivity. Differential diagnosis with psammomatous melanotic schwannoma, a feature of Carney's complex, is particularly emphasized, since dermal variants of this nerve sheath neoplasm have been described. In addition, its potential relationship with cutaneous malignant melanotic neurocristic tumour is discussed.This is, to our knowledge, the first reported case of cutaneous malignant melanoma with psammoma bodies.

The term perineurioma has been used to designate a variety of clinically and histologically different proliferations of perineurial cells based on immunohistochemical and/or ultrastructural characterization. There are two different groups of neoplasms derived from perineurial cells: extraneural or soft tissue perineuriomas, and intraneural perineuriomas. Recently, a sclerosing variant of cutaneous perineurioma has been described.We report a case of a cutaneous form of perineurioma, combining features of the intraneural and sclerosing varieties, as well as showing a Pacinian pattern of growth. In order to assess the neoplastic nature of the lesion, we performed fluorescence in-situ hybridization (FISH) analysis using a probe which maps to the chromosome band 22q11 and 22q13, allowing us to show deletion or loss of one chromosome 22 in the tumour cells.This case may be considered a new variant of perineurioma with Pacinian-like features, for which we propose the designation 'sclerosing Pacinian-like perineurioma'.

Malignant proliferating trichilemmal tumours (MPTT) are rare neoplasms capable of tissue invasion and metastasis, the diagnosis of which is based essentially on histological features. In difficult cases, however, evaluation of additional parameters may be needed to diagnose malignancy.We report three cases of MPTT in which, in addition to the histological features, we have determined the DNA ploidy, nuclear area and proliferative fraction. CD34 immunoreactivity has also been tested. Two cases were aneuploid, and one diploid with increased proliferating index. PCNA immunostaining labelled 40% and 80% of tumour cells in aneuploid tumours and 30% of the diploid neoplasm. In all cases, nuclear area was consistent with large pleomorphic tumour cells. No CD34 immunostaining was detected.Aneuploidy is common in MPTT, particularly in tumours with a high proliferative fraction. Loss of CD34 immunoreactivity is an additional feature of potential, though limited, value. Therefore, evaluation of the DNA content, proliferation markers and CD34 immunostaining may be helpful in the diagnosis of MPTT.

Electron microscopy of a case of adamantinoma of the tibia shows features which support a mesenchymal angioblastic origin rather than epithelial. Comparison is made between tissue from this tumour and a squamous cell carcinoma of the femur arising in chronic osteomyelitis. In adamantinoma no desmosomes are found between tumour cells and their cytoplasmic ultrastructure shows features of mesenchymal cell type including evidence of pinocytic activity and bundles of filaments resembling hyperplastic endothelial cells. The stroma shows features similar to fibrous dysplasia of bone with fibroblasts, histiocytes and fibrolipoblastic lipid-laden mesenchymal cells. It is condluded that adamantinoma of the tibia should be considered to be an angioblastic tumour of bone.

Twenty-seven cases of Wilm's tumour were reviewed in order to confirm the presence of nervous tissue which could imply a ‘neuroepithelial’ origin for these neoplasms. For this purpose a double-silver impregnation technique was used. Groups of ganglion cells with neurofibrils and non-myelinated axon-like processes appeared associated with a fine neurofibrillar network with neuromuscular junctions. Nervous tissue in nephroblastoma is mature and should not be confused with primary ganglioneuroblastoma of the kidney in which neuroblasts in rosette-like groupings are very numerous. A case report of such a lesion is discussed for purposes of comparison.