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Extramedullary plasmacytoma (EMP), a malignant neoplasm of the soft tissues composed of plasma cells, may occur either as a solitary plasma‐cell tumor (primary EMP) or as a manifestation of multiple myeloma (secondary EMP). We report on the aspiration cytology findings of an intriguing case of EMP of the thyroid that was initially misinterpreted as medullary carcinoma on clinical and cytologic examination. A major contributing cause for the cytologic misinterpretation was the presence of amyloid in the aspirate and the clinical impression of a “thyroid mass.” Based on this experience, we suggest that EMP should be considered in the differential diagnosis of a neck mass that yields discohesive cells associated with amyloid/amyloid‐like material. Clinical correlation and immunocytochemistry are crucial in avoiding pitfalls in this situation. Diagn. Cytopathol. 2000;23:354–358. © 2000 Wiley‐Liss, Inc.

Microsatellite instability is a frequent (13%-24%) finding in sporadic endometrial adenocarcinoma and its precursor lesions, but most studies are limited to patients who already have malignant or premalignant endometrial disease. We performed retrospective testing for microsatellite instability in women in whom cancers showing microsatellite instability developed later and prospective testing in randomly selected normal and anovular endometrial biopsy specimens. Microsatellite instability in cancer-bearing biopsy specimens accurately reflected that seen in matched malignant tissues obtained at hysterectomy. In 1 patient, microsatellite instability developed in a scanty sample of fragmented endometrial tissues 7 years before the onset of endometrial cancer. Prospective testing for microsatellite instability in the endometria of women unselected for subsequent appearance of endometrial cancer showed a very low rate of microsatellite instability. Only 1 endometrial specimen showing microsatellite instability was found among 75 anovulatory endometrial specimens, and none were found in 377 normal endometrial specimens and 46 polyps examined. Microsatellite instability may precede the onset of histologically diagnosed carcinoma but is rare in randomly sampled histologically normal endometrial tissues.

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BACKGROUND.Cytology literature on pancreatic microcystic adenoma is sparse. It is