- If the primary tumor had at least 50% clear cell histomorphology, a biopsy of the recurrent or persistent tumor is not required; the percentage of clear cell histomorphology must be documented in the pathology report or in an addendum to the original report; if slides of the primary tumor are not available for review due to disposal of slides by the histology laboratory (typically 10 years after diagnosis), biopsy of recurrent or persistent disease is required