A biopsy device includes a body, a needle, and a cutter. A motor is operable to both move the cutter relative to the needle and actuate a needle firing assembly to retract and fire the needle relative to the body. The biopsy device also includes a needle rotation assembly that is configured to substantially prevent rotation of the needle about the longitudinal axis when the needle is in a proximal position yet permit rotation of the needle about the longitudinal axis when the needle is in a distal position. A valve assembly of the biopsy device includes a slider that selectively couples a secondary lumen in the needle with either atmospheric air or saline based on the longitudinal position of the slider. The cutter passes through the slider.