Villous adenoma of the urinary tract: a lesion frequently associated with malignancy.

Villous adenomas arising in the urinary tract are rare. We identified 18 cases of villous adenomas of the bladder, urachus, and prostatic urethra. Patients ranged in age from 53 to 93 years with an average age of 69.6 years and a male preponderance of 67%. In six cases (33%), the lesion was pure villous adenoma. In three cases (17%), there was villous adenoma with in situ adenocarcinoma. In six cases (33%) there was villous adenoma with in situ and infiltrating adenocarcinoma. One case (6%) had villous adenomas with in situ (noninvasive) papillary urothelial carcinoma. One case (6%) had villous adenomas with in situ adenocarcinoma and in situ papillary (noninvasive) and infiltrating urothelial carcinoma. The remaining case (6%) had villous adenoma with in situ and infiltrating adenocarcinoma and in situ (noninvasive) papillary and infiltrating urothelial carcinoma. Clinical outcome was available in eight of the cases, with a mean follow-up of 4.6 years. No evidence of recurrence was found in two patients with pure villous adenoma or in two patients with villous adenoma and only in situ adenocarcinoma, all of whom were treated by nonradical excision. However, two of three cases with infiltrating cancer developed distant metastases despite radical surgery; the remaining patient was disease-free 11 years after transurethral resection. The case with villous adenoma and in situ urothelial carcinoma progressed to sarcomatoid urothelial carcinoma following partial cystectomy. Eight of 10 villous adenomas cases studied expressed the epitope for mAbDas1, found on colonic epithelium and primary adenocarcinomas of the bladder and urachus but not on normal or neoplastic urothelium. This study expands the spectrum of histologic features accompanying villous adenomas of the urinary tract. Coexisting infiltrating adenocarcinoma is often present, necessitating thorough sampling of any lesion diagnosed by biopsy as villous adenoma. Pure villous adenoma and those well-sampled lesions also containing in situ adenocarcinoma portend a favorable prognosis, even without radical treatment. Coexisting in situ or infiltrating carcinoma suggests a more aggressive course. Histologically, immunohistochemically, and prognostically, these lesions appear analogous to their counterparts in the intestine.