Perforin (P1) is a cytolytic protein with similarity to complement component C9. P1 has been described as a unique component of murine cytolytic T-cell and rat natural killer cell granules Previous studies indicated that human granules and P1 differed from murine granules and P1 in that they appeared to be cytolytically less active and lacked the haemolytic activity characteristic of P1. It has been suggested that P1, like C9, is under the control of the homologous restriction factor. Here we determine the primary structure of human P1, re-examine its functional properties, and address the question of homologous restriction.

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Hyalinizing clear‐cell carcinoma (HCCC) is a recently described distinctive salivary gland neoplasm. Because of its cytoplasmic clearing and the bland nuclear features, HCCC resembles other tumors. The authors describe the cytomorphologic features of four cases of HCCC in fine‐needle aspirates (FNA) and discuss the differential diagnosis. Fine‐needle aspirates from 4 patients with primary HCCC of minor salivary glands were reviewed. Smears were stained with Diff‐Quik and Papanicolaou stains. The cytologic features of the epithelial and the stromal components were analyzed. Cell blocks were prepared, and findings were correlated with prior or subsequent surgical specimens in each case. The smears contained numerous cohesive small and large epithelial cell groups and sheets which had sharp outlines and showed focal nuclear overlapping. The cells had uniform round to ovoid nuclei, granular chromatin, and small nucleoli. The abundant, well‐defined cytoplasm was clear in many cells but denser in others. No myoepithelial cells or hyaline globules were identified. HCCC seems to have characteristic cytomorphologic findings on FNA smears. Because these cytologic features are not specific, and overlap with those of a number of salivary gland neoplasms that contain clear cells, a high level of suspicion, clinico‐pathologic correlation, and examination of cell blocks are necessary to suggest the diagnosis. A diagnosis of HCCC by FNA was suspected in 3 of the 4 cases reported here. Diagn. Cytopathol. 2000;23:333–337. © 2000 Wiley‐Liss, Inc.

Three uterine tumors, each consisting of endometrioid carcinoma and Ewing's sarcoma/peripheral primitive neuroectodermal tumor (ES/pPNET) are described. The diagnosis of ES/pPNET in each case was first established in the hysterectomy specimen because each ES/pPNET was misinterpreted on the endometrial biopsy specimens as a high-grade homologous sarcoma. The ES/pPNET element in each case consisted of solid masses of small- to medium-sized round cells without Homer-Wright pseudorosettes, glial or ganglion cells, true rosettes with central lumens, or medulloepithelial tubules. Each ES/pPNET exhibited focal positive immunostaining for neuron-specific enolase, diffuse staining for vimentin, and strong cell membrane immunoreactivity for O13 (CD99), the last finding providing the first clue to the diagnosis of ES/pPNET in each case. The diagnosis in each case was confirmed by detection of EWS/FLI-1 fusion transcript through reverse transcription polymerase chain reaction. We also examined O13 immunoreactivity retrospectively in 40 cases of malignant mixed mullerian tumors (MMMT) with homologous or heterologous elements. O13 immunoreactivity was not observed in the malignant epithelium or in the homologous or heterologous sarcomas. The immunoreactivity of O13 in round cell endometrial sarcomas provides a clue to the diagnosis of ES/pPNET.