The number of nuclear pores per sq micron was determined on the freeze-fractured nuclei of 20 human bladder tumors and five control samples of normal bladder epithelium. Measurements of the nuclear surface and volume were also performed, and the mean number of pores per nucleus and the ratio of pore to volume were calculated. The DNA distribution pattern on the same samples was determined by flow cytometry. All control samples and 12 tumors were diploid, and eight tumors were aneuploid. The

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... number of pores per sq micron and mean total number of pores per nucleus in the control samples and in diploid tumors were similar. In the aneuploid tumors, both values were significantly higher. However, the ratio of pore to volume was shown to be constant regardless of the DNA content. It was further observed that, in aneuploid tumors, there are two populations of nuclei, one with density of pores similar to the diploid tumor and one with a higher pore density. Because aneuploid bladder tumors have been shown to have more aggressive behavior than diploid tumors, increased density of nuclear pores or their total number per nucleus may be related to tumor behavior. This view is supported by the observation that five of eight tumors with increased density and total pore number were invasive, while all tumors with low pore number were noninvasive.