Assessment of Tumor Budding and T1 Substaging as Histopathological Predictors of Outcome in Urothelial Bladder Carcinoma

Bladder carcinoma remains a major global oncological burden, exerting a substantial impact on patient morbidity and mortality. In Egypt, it constitutes a significant public health concern with distinctive epidemiological characteristics. While squamous cell carcinoma historically predominated, a substantial shift has occurred over recent decades, and urothelial carcinoma has emerged as the dominant subtype, accounting for approximately 75-80% of cases.

Pathological assessment traditionally focuses on histological grade and invasion depth. The precise assessment of invasion depth is critical, particularly in T1 non-muscle-invasive urothelial carcinoma, where the tumor invades the lamina propria. Multiple sub-classification systems exist for T1 tumors, including anatomical approaches relative to the muscularis mucosae and semiquantitative micrometric methods, yet no single method has been adopted universally. Furthermore, in muscle-invasive disease, the morphology of the invasive front provides crucial biological insights. Tumor budding, defined as single isolated cancer cells or small clusters of fewer than five cells at the invasive front, is recognized as a morphological hallmark of epithelial-mesenchymal transition (EMT) and reflects aggressive tumor potential.

This study evaluates archived hematoxylin and eosin (H&E)-stained slides from patients who underwent transurethral resection (TUR) for urothelial carcinoma between 2018 and 2024. Histological subtypes will be confirmed according to the 2022 World Health Organization (WHO) classification, and tumor grade and stage will be determined using the American Joint Committee on Cancer (AJCC) 8th edition. Additional pathological parameters assessed will include tumor size, multifocality, coagulative tumor necrosis, lympho-vascular invasion (LVI), and perineural invasion (PNI).

The histopathological procedures are divided into two primary evaluations:

• pT1 Substaging: Confirmed pT1 cases will undergo rigorous histopathological substaging. Anatomical substaging (T1a/b/c) will identify the invasion level relative to the muscularis mucosae. Micrometric assessment will utilize a 0.1 mm threshold for semi-quantitative subtyping, alongside the Rete Oncologica Lombarda (ROL) system, which uses a 1.0 mm threshold to define low-risk and high-risk progression groups.
• Tumor Budding Assessment: Confirmed pT2 cases will be evaluated for tumor budding at the invasive front using the "Hotspot" method to count buds in one high-power field. Cases will be stratified into three grades: Low Budding (BD1: 0-4 buds), Intermediate Budding (BD2: 5-9 buds), and High Budding (BD3: ≥ 10 buds).