A biopsy device comprises a targeting set assembly, a probe assembly, and a holster assembly, which are detachable from one another. The targeting set assembly comprises a needle assembly having a tissue piercing tip, a tissue receiving aperture, and a fluid sealing mechanism. The probe assembly comprises a tissue cutter and an internal helix mechanism. The internal helix mechanism may fully retract the cutter within the probe assembly to prevent exposure to the sharp distal end of the cutter when the probe assembly is detached from the needle assembly. When the probe assembly and needle assembly are connected, the internal helix mechanism may extend the cutter into the needle to facilitate biopsy of a tissue sample. The helix may have variable pitch for providing a first translational speed for cutting with the cutter and a second translational speed for cutter retraction.