Urachal Adenocarcinoma associated with villous adenoma
Primary adenocarcinoma of the bladder is rare, representing approximately 2% of malignant bladder tumors. It is thought that primary adenocarcinoma arises in the bladder by one of two mechanisms. The first is malignant transformation of cystitis glandularis, associated with metaplastic intestinal-type mucosa. The second proposed mechanism is through malignant transformation of the glandular epithelium lining urachal remnants. The precursor lesion for both of these mechanisms is thought to be intestinal metaplasia, and so villous adenomas can be seen in association with lesions developing in both scenarios.
The urachus is a tubelike structure formed in the embryo as the allantois involutes, and extends from the dome to the umbilicus. Urachal remnants, or remnants of allantois remaining after birth, may develop into cysts or epithelial neoplasms, such as urachal adenocarcinoma. Patients with urachal adenocarcinoma typically present in the fifth or sixth decade with nonspecific urinary tract symptoms. The clinical workup reveals a lesion in the dome of the bladder.
Histologically, the urachal adenocarcinoma is a high-grade glandular lesion, exhibiting enteric, mucinous, or signet ring morphology, or a mixture of these subtypes. The mucinous subtype is seen most commonly. The urachal remnant from which the lesion arises is only identified in a subset of cases. Absence of a definitive urachal remnant in the specimen, coupled with the similarity between the histologic morphology of this diagnosis with that of primary colorectal adenocarcinoma, make urachal adenocarcinoma a potentially challenging diagnosis.
Johnson et al proposed three criteria to rule out diagnoses in the differential, such as metastatic colorectal adenocarcinoma or urothelial carcinoma with glandular differentiation, and effectively rule in urachal adenocarcinoma by exclusion. The first is the location in the bladder dome. The second is background (nonurachal) bladder lacking in situ carcinoma or glandular differentiation. Finally, a thorough clinical workup is required to rule out another primary adenocarcinoma that may have metastasized.
Urachal adenocarcinoma can show immunoreactivity for both CK20 and CK7, in addition to CDX2. Two immunohistochemical stains that may be helpful are beta-catenin, which shows diffuse nuclear positivity in colonic adenocarcinoma but is rarely positive in urachal adenocarcinoma, and CEA, which is diffusely positive in urachal adenocarcinoma but positive in only 29% of nonurachal bladder adenocarcinomas.
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Contributed by Kate Serdy, MD and Anil Parwani, MD, PhD