Invasive urothelial carcinoma in association with surface low-grade papillary urothelial carcinoma: clinical and pathologic insights from a rare entity.

Abstract

Surface low-grade papillary urothelial carcinoma with an invasive phenotype represents an understudied entity with its clinical behavior, therapeutic responses, and long-term outcomes remaining poorly defined. We evaluated 17 patients from a single institution with histologically confirmed surface low-grade papillary urothelial carcinoma with an invasive phenotype, followed by longitudinal clinicopathologic analysis to delineate disease trajectories and treatment outcomes. Surface components of all tumors in this cohort demonstrated a low-grade papillary urothelial carcinoma phenotype. At the initial presentation, 53% of patients had invasive disease, while 47% were diagnosed with noninvasive disease. During follow-up, 37% of those with noninvasive disease appeared to progress to invasive disease within 1 year. At the point when invasive disease was diagnosed, pT1 disease was observed in 77% cases, and pT2-4 was observed in 23%. During subsequent follow-up, 77% of patients experienced recurrences, with 41% requiring therapeutic escalation to intravesical Bacillus Calmette-Guérin or systemic chemotherapy for disease progression. High-grade recurrence was identified in 23% patients. Distant metastases developed in 18% of patients, preferentially involving the lungs and bone. The median survival of the cohort was 66 months, and 1 patient died of disease. These findings underscore the variable and unpredictable course of this disease phenotype, emphasizing its potential for aggressive evolution despite surface low-grade tumor histology. Vigilant surveillance and early consideration of definitive treatment may be a prudent strategy to mitigate progression risks in this rare subset of patients.