'Cannibalism' (cell phagocytosis) does not differentiate reactive renal tubular cells from urothelial carcinoma cells

Objective: Cannibalism of one cell by another in voided urine cytology has been considered a cytological feature for differentiating urothelial carcinoma (UC) from benign lesions. Recently, however, we observed cannibalism in voided urine obtained from patients with renal glomerular disease (RGD). The purpose of this study was to determine the cytomorphological and immunocytochemical characteristics of cannibalism in voided urine from RGD. Methods: Seventy cytology specimens of voided urine were examined and the findings were compared with the histological findings. In addition, we compared the cytomorphological and immunocytochemical differences in cannibalism found in RGD and cases of UC selected as showing cannabilism. Results: Cannibalism in voided urine was found in three (5.5%) of 55 RGD cases. The finding was measured as (1+) < 5 cells, (2+) 5–20 cells, and (3+) > 20 cells and was (1+) in all three RGD cases, compared with 6.7%, 60% and 33.3% respectively in 15 UC cases. Differences in low cellularity cases (1+) and moderate to high cellularity cases (2+ or 3+) were statistically significant between RGD (3 and 0) and UC (1 and 14) (P=0.005). The maximum diameter of cannibalized cells in RGD was 24.3–33.0 μm (mean 29.8 μm) versus 18.0–30.4 μm (mean 23.3 μm) in UC (P=0.004). Necrosis and isomorphic erythrocytes were absent in RGD, but were found in 46.7% and 86.7%, respectively, of UC cases (P=0.245 and P=0.012). Dysmorphic erythrocytes were identified in all three cases with RGD and 13.3% of UC (P=0.012). Vimentin reactivity was found in all cases with cannibalism in RGD, but never in UC (P=0.001). Conclusions: Our results demonstrated that cannibalism in voided urine is present not only in UC but also in RGD. Furthermore, we showed that cellularity of cannibalism, vimentin reactivity and background differed significantly and can be used for differential diagnosis between the two groups.