Transitional refers to the histological subtype of the cancerous cells as seen under a microscope.
The 1973 WHO grading system for TCCs (papilloma, G1, G2 or G3) is most commonly used despite being superseded by the 2004 WHO [REF] grading (papillary neoplasm of low malignant potential [PNLMP], low grade, and high grade papillary carcinoma).