Background. Papillary renal tumors lack alterations of chromosome 3 and show trisomy of chromosomes 7 and 17, genotypic features distinct from nonpapillary carcinomas. Methods. The authors examined 39 papillary renal neoplasms to identify morphologic features allowing distinction of high grade from low grade tumors. Twenty‐nine papillary tumors and 13 nonpapillary tumors were examined for the presence of trisomy of chromosome 7 using fluorescence in situ hybridization. Data recorded included tumor size, stage, grade, architectural pattern, and the presence of glycogen, foam cells, and iron. Results. Nineteen tumors were classified as low grade and 20 as high grade. The high grade tumors more often formed tall papillae with solid and tubular areas and had more intracellular glycogen, whereas the low grade tumors were more often trabecular. There was no significant difference in tumor size or iron deposition. High grade tumors were of higher stage. Foam cells more commonly were noted in low grade tumors. Sixty‐seven percent of low grade, 43% of high grade, and none of the non‐papillary tumors showed trisomy of chromosome 7. Metastases developed only in patients with high grade papillary tumors (10/19, 7 within 2 years of diagnosis), all of whom died of disease. Conclusions. Papillary renal carcinomas with high nuclear grade are more likely to behave in an aggressive fashion, whereas those with low nuclear grade may be associated with longer disease free survival. Furthermore, trisomy of chromosome 7 can be identified by fluorescence in situ hybridization and is useful in differentiating true papillary from nonpapillary renal neoplasms. Cancer 1995; 76:669–73.

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