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Notes: To study the clinical and pathological features of primary malignant peripheral primitive neuroectodermal tumours (PNETs) of the skin and subcutaneous tissue, to discuss the differential diagnosis, and to review the existing literature on these tumours.〈section xml:id="abs1-2"〉〈title type="main"〉Methods and results:Eight cases of PNETs presenting in the skin and subcutaneous tissue were identified from the pathology records of the Christie Hospital, Manchester. Detailed immunohistochemical studies were performed on all cases and seven tumours were subjected to electron microscopic examination. Detailed clinical and follow-up information was obtained on seven cases. Six tumours occurred in children and adolescents and two were seen in young adults (age range, 8–36 years). No sex or site predilection was observed. Five tumours occupied the dermis and subcutis and three were entirely located in the subcutaneous tissue. Microscopically, they were composed of small round cells and seven tumours contained glycogen. Only one tumour focally exhibited Homer–Wright rosettes and neuropil. Two tumours contained rhabdoid or plasmacytoid cells in places and all cases showed microcystic and pseudovascular spaces. Immunostains revealed MIC2 (8/8), NSE (7/8), PGP9.5 (7/8), β2 microglobulin (7/8), neurofilament protein (6/8), S100 protein (3/8), synaptophysin (2/8) and Leu-7 (1/8) positivity. Anomalous cytokeratin (4/8), desmin (2/8), myoglobin (2/8), NKIC3 (4/8) and GFAP (1/8) staining was also noted. Ultrastructurally, neuroendocrine granules were detected in five cases and one case exhibited microtubules in processes. Adequate follow-up information was available in four cases. One patient died of metastatic disease. One child developed axillary lymph node metastasis but is alive with no evidence of disease 96 months after treatment. Two other patients are alive with no residual or recurrent disease 44 and 52 months after excision and radio/chemotherapy.〈section xml:id="abs1-3"〉〈title type="main"〉Conclusion:PNETs are rare malignant small round cell tumours of the skin and subcutaneous tissue which are probably underdiagnosed. A correct diagnosis can be made on light microscopic features, demonstration of neuroendocrine granules on electron microscopy and a combination of MIC2, β2 microglobulin, and more than one neural marker positivity. These neoplasms should be differentiated from other cutaneous neoplasms composed of small round cells. The number of cases of cutaneous PNETs studied so far is rather small, and no firm conclusion can be drawn about their behaviour but long-term survival is possible in some cases.

Notes: Aims: We describe the cutaneous pseudoneoplastic lesions in two patients with nodular erythema elevatum diutinum, a rare chronic disorder in which polymorph nuclear fragmentation (leukocytoclasis) is present within dermal nodules showing spindle cells and fibrosis. In both cases diagnostic difficulty was encountered clinically and pathologically and various benign and malignant neoplasms were considered in the differential diagnosis. Methods and results: Immunohistochemically the spindle cells were negative for CAM5.2, AE1/3, S100 protein and desmin (D33). They were positive for vimentin and focally positive for CD34 and α-smooth muscle actin. Some of the spindle cells were positive for Mac 387 and KP1(CD68). By electron microscopy, the lesions were shown to consist of fibroblasts/myofibroblasts and fusiform macrophages. Conclusions: Increased awareness of the features described will help to avoid misdiagnosis as a neoplastic process.

Notes: An immunohistochemical study of 106 malignant melanoma specimens from 59 patients, using formalin-fixed, paraffin-embedded material, is reported. Negativity for HMB-45 was seen in 11% of specimens. The rate of positivity with CAM 5.2 was 7%. One specimen showed α-smooth muscle actin (αSMA) positivity. For 11 of the 12 cases in which anomalous immunophenotypes were seen, multiple specimens were available; nine of these showed evidence of an alteration in the immunophenotype between specimens. Comparing the primary tumours with local recurrences and metastases, there was, variously, loss of HMB-45, S-100 protein and NKI/C3 positivity, and acquisition of CAM 5.2 and αSMA positivity. In some cases, the change of immunophenotype appeared to occur in a single step. However, one case with six consecutive specimens showed evidence of progressive loss of HMB-45, S-100 protein and NKI/C3 with concomitant gain of CAM 5.2 staining. The implications for the use of immunophenotyping in diagnostic practice are discussed.

Notes: The clinical, histological and immunohistochemical findings in five primary lymphomas of the urinary bladder are reported. One patient had both lymphoma and transitional cell carcinoma of the bladder. All of the lymphomas showed histological features of mucosa-associated lymphoid tissue (MALT) lymphomas with centrocyte-like cells in all cases. One patient with pre-existing cystitis glandularis showed lymphoepithelial lesions. Biopsies from four patients contained reactive germinal centres and, in two of these, there was follicular colonization by tumour cells. In three patients, repeat biopsies, over several years, showing the changes of MALT lymphoma, were diagnosed as cystitis. We suggest that a large proportion of primary lymphomas of the bladder are lymphomas of MALT and that the characteristic morphological and immunohistochemical features of these tumours should be sought in biopsies containing large numbers of lymphoid cells.