High-grade urothelial carcinoma invading detrusor muscle (muscularis propria). Such cases are classified as T2 tumors in the TNM system. They are subdivided into T2a (invading inner half of detrusor) and T2b (invading outer half). This distinction should not be attempted in TUR specimens since they are often fragmented and poorly oriented. Only cystectomy specimens are suitable for substaging T2 tumors.