1. An ultrasound diagnostic apparatus comprising: an ultrasound probe configured to transmit ultrasound waves to a subject and receive an echo, the subject including a breast; a location sensor configured to detect a location of the ultrasound probe; at least one processor configured to: calculate a location of echo data in a first coordinate system in a three-dimensional space having a certain point as an origin based on the probe location detected by the location sensor; perform a deformation calculation to deform a shape of the breast, in a first position, in a first image of an ultrasound image based on one of the echo data and a medical image captured in advance by a medical imaging apparatus other than the ultrasound diagnostic apparatus, to a shape of the breast in a second position, in a second image of one of the ultrasound image and the medical image, the ultrasound image having the first coordinate system, wherein each of the first position and the second position is one of a prone position, a supine position, and a standing position such that the first position is different than the second position; perform a coordinate conversion between the first coordinate system of the ultrasound image and a second coordinate system of the medical image; and display a deformed image based on the deformation calculation by the at least one processor and the second image about a same cross-section on a display device.