A device and system for accessing and anchoring a patient's sentinel lymph node after a radiopharmaceutical is injected at or near a lesion site within a patient's body. The migration of and accumulation of the radiopharmaceutical in a sentinel node of the patient is monitored from outside the patient's body. The sentinel node can then be accessed through a cannula and an anchoring device may be employed to fix the location of the sentinel node. The anchoring device has at least one radially extending members which penetrate into the sentinel node. Preferably, the radially extending members are RF powered to facilitate entry into the sentinel node. With the anchor device secured to the sentinel node as a locator, subsequent procedures may be performed.