an apparatus and method are provided for precisely isolating a target lesion in a patient &# 39 ; s body tissue , resulting in a high likelihood of “ clean ” margins about the lesion when it is removed for diagnosis and / or therapy . this approach advantageously will often result in the ability to both diagnose and treat a malignant lesion with only a single percutaneous procedure , with no follow - up percutaneous or surgical procedure required , while minimizing the risk of migration of possibly cancerous cells from the lesion to surrounding tissue or the bloodstream . in particular , the apparatus comprises a biopsy instrument having a distal end adapted for entry into the patient &# 39 ; s body , a longitudinal shaft , and a cutting element disposed along the shaft . the cutting element is actuatable between a radially retracted position and a radially extended position . advantageously , the instrument is rotatable about its axis in the radially extended position to isolate a desired tissue specimen from surrounding tissue by defining a peripheral margin about the tissue specimen . once the tissue specimen is isolated , it may be segmented by further manipulation of the cutting element , after which the tissue segments are preferably individually removed from the patient &# 39 ; s body through a cannula or the like . alternatively , the specimen may be encapsulated and removed as an intact piece .