A vaccine undergoing testing at the Mayo Clinic has reportedly removed cancer cells in a breast cancer patient.

Florida resident Lee Mercker became the first patient to participate in a clinical trial for a new vaccine after being diagnosed in March with early-stages of the disease.

She told First Coast News she had “DCIS stage zero” breast cancer, meaning the cancer cells had not yet spread. She was left with three options -- have a lumpectomy where the cancer cells are removed, undergo a mastectomy where the breasts are removed, or join a clinical trial for a potentially life-saving vaccine to kill the cells and prevent them from coming back.

FORMER NFL RUNNING BACK DEANGELO WILLIAMS SPONSORS 500 MAMMOGRAM SCREENINGS AFTER MOM'S BREAST CANCER DEATH

“I signed on the dotted line that day," Mercker said of the 12-week trial at the clinics Jacksonville campus.

“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.

Mercker said the process entailed a series of shots and tests.

“They always took your blood, you had a physical, they’d make your shot right there on the spot for you,” Mercker said. “It was three shots, all in a row, alternating arms, four shots, two weeks apart.”

“It’s supposed to be just off the shelf, kind of similar to when you get the flu shot or pneumonia shot,” Chumsri said.

CLICK HERE TO GET THE FOX NEWS APP

She 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.

The treatment is being used on another patient who is reportedly showing positive results.

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