A biopsy needle assembly may include a sample needle, an actuator and a cutter. A sample needle may include a sample opening. A tissue sample may be positioned in the sample opening when the sample needle is inserted into tissue of a patient. The actuator may be activated to move the cutter relative to the sample needle and separate sample tissue in the sample opening from adjacent tissue. The biopsy needle assembly may be removed from the patient and the sample may be removed from the sample opening. In some embodiments, the sample needle may be inserted in tissue through an instrument (e.g., an endoscope). The biopsy needle assembly may include a sheath that inhibits a sample needle and a cutter from contacting the instrument when the biopsy needle is inserted in the instrument.