It depends where a patient is in their breast cancer journey.
In the beginning of breast cancer diagnosis, a CT or oftentimes a PET scan (a CT that tumors light up on) is used to look for distant disease beyond the breast. Breast cancer can be by itself in the breast, it can spread to the lymph nodes, then in late stages it can spread to places such as the lung, liver, bones, or brain.
CT scans are interpreted by radiologists. Typically this means that there is a period of days before the CT scan report is made available to the breast cancer doctor. The breast cancer doctor then reviews the report with the patient at their next visit. Depending on the results of a CT scan, many things can happen. Typically, if a cancer is still in the breast and lymph nodes, surgery will be performed and chemo or radiation may follow. If cancer has spread to distant sites, chemo would be the main treatment course.