Abstract: A medical instrument including a cannula or probe used to penetrate tissue to a target area to perform a medical procedure including biopsy and RF ablation of undesirable tissues or cells for treatment, or to prevent the spread of cancer cells during a biopsy procedure. The probe is preferably shape changeable. The probe may be hollow or solid having an exterior surface coated with a dielectric material, a preferably sharpened beveled tip at a distal end coated with a resistor material, and means for coupling the probe to an RF generator and control device. The RF generator provides current to the probe. The dielectric material provides a predominant impedance characteristic of the probe in contact with tissue, thus changes in impedance will vary primarily based on the area of the probe in contact with tissue.