Stage 0a: Superficial, non-invasive; treated by removal.
Stage 0is: Carcinoma in situ (CIS), high-grade but confined to the lining.
Stage I: Invades lamina propria but not muscle.
Stage II: Invasive, reaching bladder muscle.
Stage III: Extends to surrounding tissues (e.g., perivesical tissue, prostate, uterus).
Stage IV: Advanced, spreading to lymph nodes or distant organs.