Unusual immunostaining pattern of chromogranin in normal urothelium and in transitional cell neoplasms

We report an unusual pattern of immunostaining for chromogranin A in 24 transitional cell carcinomas (TCC). Positive immunostaining was seen with chromogranin A antisera in 10 of 16 urinary bladder TCC, neither of 2 prostatic TCC, 3 of 3 ureteral TCC and 2 of 3 metastatic TCC. This staining was demonstrated within the cytoplasm of transitional cells at all levels of the neoplastic epithelium, including cells near the basement membrane and at the free surface (umbrella cells). In 5 of 7 cases there was also immunoreactivity of the non-neoplastic urothelium. Immunostaining with neuron-specific enolase and synaptophysin was negative in all of these cases and no neuro-secretory granules were identified in 7 cases examined by electron microscopy. This pattern of immunostaining is probably due to reactivity with chromogranins or certain chromogranin-like proteins in the transitional cells, particularly in the umbrella cells.