A treatment instrument comprises an end effector and a plunger. The end effector comprises a plurality of cutting features and an interior cavity. At least a portion of the plunger is slidably positioned within the interior cavity of the end effector. The plunger comprises a distal head attached to the distal end of a central shaft. The plunger is configured to rotate within the end effector, and comprises a cutting member that is operable to mince tissue specimens captured by the cutting features of the end effector. An alternative treatment system comprises an end effector, a plunger, and a plug. The central shaft of the plunger and the plug are slidably located within an inner tube of the end effector, with the plug being positioned distal to the central shaft.