JACKSONVILLE, Fl. – A vaccine undergoing testing at the Mayo Clinic has removed cancer cells in a breast cancer patient, says Fox13News.

Florida resident Lee Mercker told First Coast News she had “DCIS stage zero” breast cancer, meaning the cancer cells had not yet spread. Mercker became the first patient to participate in a clinical trial for a new vaccine once she chose to “[sign] on the dotted line that day,” after being given the choices of a lumpectomy, a mastectomy, or joining the clinical trial.

“It’s supposed to stimulate a patient’s own immune response so that the immune cells like t-cells would go in and attack the cancer,” said Dr. Saranya Chumsri, an oncologist at the world-renowned medical center, “It’s supposed to be just off the shelf, kind of similar to when you get the flu shot or pneumonia shot.”

Merker was still required to get a mastectomy to make sure everything was removed properly. Researchers can view the breast tissue to access how the vaccine works.

Chumsri said clinical trials for patients with other stages of cancer are also showing good results.