Tissue biopsy is performed through a central passage of a cannula covered with a protective sleeve. The protective sleeve is attached at one end to a location at or near a distal end of the cannula. After the biopsy procedure is completed, the cannula is withdrawn so that its exterior slides through the sleeve. In this way, the trailing edge of the sleeve is invaginated within the proximal portions of the itself to envelop the sleeve exterior and reduce the risk of inadvertent tumor cell seeding.