Contiguous but dissimilar epithelial neoplasms of the urinary bladder.

An unusual tumour of the urinary bladder is described. It consists of two distinct nodules each with a quite different histological appearance, one being mucus-secreting adenocarcinoma, the other transitional cell carcinoma. Where the nodules are in contact there is little intermingling of the two histological patterns and it is suggested that the findings are probably due to the collision of two separate neoplasms. Metaplastic changes are present in the bladder mucosa adjacent to the tumour. The significance of these changes in the pathogenesis of adanocarcinoma is discussed.