A biopsy device and method are provided for obtaining a tissue sample, such as a breast tissue biopsy sample. The biopsy device includes a disposable probe assembly with an outer cannula having a distal piercing tip, a cutter lumen, and a cutter tube that rotates and translates past a side aperture in the outer cannula to sever a tissue sample. The biopsy device also includes a reusable hand piece with an integral motor and power source to make a convenient, untethered control for use with ultrasonic imaging. The reusable hand piece incorporates a probe oscillation mode to assist when inserting the distal piercing tip into tissue. A saline valve positioned by the reusable hand piece communicates a saline supply through the probe assembly to perform saline flush of the cutter tube and outer cannula.