Nephrogenic Adenoma Intermixed With Urothelial Carcinoma

Context.— Nephrogenic adenoma (NA) is a common urinary tract lesion typically associated with urothelial disruption, leading to implantation of shed renal tubular cells. NA may demonstrate a spectrum of architectural and cytologic features mimicking urothelial carcinoma (UC), adenocarcinoma (including clear cell adenocarcinoma and prostatic adenocarcinoma), and invasion. However, admixed UC and NA has not been described. Objective.— To describe cases where the NA was intimately intermixed with UC, potentially mimicking variant differentiation or invasion. Design.— In 3 health care systems we identified specimens of NA and UC intimately intermixed with each other to the extent that they could mimic a spectrum of one lesion. We assessed patterns of NA and clinical implications of misdiagnosing NA as glandular differentiation of UC. Results.— There were 4 women and 29 men (median age, 72 years; range, 31–89 years). Twenty-four patients had transurethral resections, 3 had biopsies, and 6 had major resections. Fourteen had noninvasive high-grade papillary UC, 6 had carcinoma in situ, and 11 had invasive high-grade UC. In 2 patients, NA developed in a papillary urothelial neoplasm with extensive denudation. Three patients had fibromyxoid NA infiltrated by invasive UC. Classical NA (n = 30) had tubulopapillary (n = 18), pure tubular (n = 7), or pure papillary architecture (n = 5). In 1 lesion, NA was present in muscularis propria, and 2 lesions involved adventitia. NA could have been misdiagnosed as invasion in 17 of 22 (77%) noninvasive tumors or higher stage in 19 of 33 (58%). Conclusions.— NA can be intermingled with high-grade UC, expanding the spectrum of entities that must be considered in the differential diagnosis, as it may mimic glandular or tubular differentiation, invasion, and a higher stage of disease. Misinterpretation of NA in such a setting may incorrectly convey a more aggressive biological potential of cancer to clinicians.