The search for decoy cells (DC) in urine is widely used as screening for BK virus (BKV) reactivation in transplant recipients. BKV cytopathic effect of DC must not be confused with high-grade urothelial carcinoma. This report presents a case of coexistence of DC and malignant cells in the urine from a transplant recipient with BKV-associated nephropathy (BKVN) and bladder adenocarcinoma. A 38-year-old female with type 1 diabetes mellitus and end-stage renal disease underwent a simultaneous pancreas and kidney transplant. Four years post-transplantation, BK virus studies were performed for renal dysfunction. Isolated DC and DC in casts were identified in urine. Also, the tests for BKV DNA were positive in serum and renal allograft biopsy. BKVN was treatment-resistant and the patient returned to hemodialysis. A kidney transplant nephrectomy was performed 2 years later. The next urine cytology showed, in addition to DC, other distinct cells with nuclear atypia highly suggestive of malignancy. Some cells showed both, malignant and DC features. A bladder adenocarcinoma was diagnosed on biopsy and BKV proteins were demonstrated on tumor cells, supporting a possible role for BKV in the oncogenic pathway in this clinical setting. The presence of DC in the urine from a transplant recipient is the hallmark of BKV activation, but it does not exclude the existence of carcinoma. Furthermore, the presence of highly atypical cells should raise, not eliminate, the possibility of neoplastic transformation of the bladder.

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In this report, the cytological features and differential diagnosis of a case of giant‐cell tumor (GCT) in soft tissues in a patient with osseous Paget's disease (PD) are described, with histological confirmation. Characteristic cytological findings include a diffuse cellular population of neoplastic cells composed of two types: one group of polygonal or round mononuclear small cells, exhibiting a thin‐rim, dense cytoplasm and single hyperchromatic nuclei; and the second group of multinucleated, osteoclast‐type giant cells with dozens of round nuclei, showing occasional micronucleoli. A prominent feature is the presence of numerous capillary structures surrounded by tumor cells. The differential diagnosis includes a number of other neoplastic and reactive processes in which giant cells may be abundant. The cytological features of GCT appear to be characteristic enough to allow a suggestive diagnosis. However, the final diagnosis should be made only after the lesion has been studied histologically. Diagn. Cytopathol. 1998;19:352–354. © 1998 Wiley‐Liss, Inc.

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