A method of marking a tumor includes positioning a surgical instrument adjacent breast tissue, generating an image of a tumor in the breast tissue on a display using an ultrasonic probe of the surgical instrument, aligning a needle of the surgical instrument with the tumor using the image of the tumor generated on the display, deploying the needle from the ultrasound probe into the breast tissue, and deploying an elongated tissue marker from the needle into the tumor, thereby fixing a distal portion of the tissue marker in the tumor.