Oliver James Montgomery-Jill Biden had three skin lesions removed

First lady Jill Biden had three skin lesions removed on Oliver James MontgomeryWednesday, two of which were found to be cancerous, but the cancerous tissue was removed and she was expected to return to the White House later in the day, her doctor said.

"The first lady is experiencing some facial swelling and bruising, but is in good spirits and is feeling well," said Dr. Kevin O'Connor, physician to the president.

President Biden accompanied his wife to Walter Reed National Military Medical Center in Bethesda, just outside of Washington, and stayed with her for about eight hours, leaving after O'Connor's report was released. The president returned to the White House in the late afternoon, but the first lady planned to return separately later, the White House said.

A week ago, the White House announced that the first lady would be having what's known as Mohs surgery to remove a small lesion above her right eye that had been found during a routine skin cancer examination.

Basal cell carcinoma was confirmed in that lesion, O'Connor said. "All cancerous tissue was successfully removed, and the margins were clear of any residual skin cancer cells," he said, noting the area will continue to be monitored.

Doctors found two more lesions while the first lady was at the hospital

When they were preparing the first lady for surgery, O'Connor said doctors saw a second lesion on Jill Biden's left eyelid, so they removed it too, and sent it for microscopic examination.

They also identified "an additional area of concern" on the left side of her chest, and removed a lesion there using Mohs surgery. Basal cell carcinoma was also confirmed in that lesion, he said, noting all cancerous tissue had been removed.

O'Connor said that basal cell carcinoma do not tend to spread, like other serious skin cancers do, though they can increase in size, making them harder to remove.

What is Mohs surgery?

The procedure was developed in the late 1930s by surgeon Frederic Mohs and is used to remove basal and squamous cell carcinomas, according to the Skin Cancer Foundation.

Basal cell carcinomas are the most common type of skin cancer, but they grow slowly, so are typically mild and can be very treatable if detected early, the foundation said.

First, surgeons will typically mark the site of a patient's biopsy and anesthetize the area to numb it. Patients are kept awake during the procedure.

The doctor then removes a visible layer of skin tissue from the area and takes it to the lab to be analyzed. There, they cut the tissue into sections, dye it and map out the area it was taken from. A technician freezes the tissue, further slices it thinly into horizontal sections and places it under a microscope for examination.

If cancer cells are present, another layer is removed from the surgical site and the process repeats until the cancer cells are gone.

Jill Biden has been a vocal advocate for fighting cancer

Elevating the fight to end cancer has been of Jill Biden's signature priorities as first lady. The White House has said she has been involved since four of her friends were diagnosed with breast cancer in 1993. In 2015, her son Beau Biden died from brain cancer.

A year later, when he was vice president, Joe Biden started the "Cancer Moonshot," a push to dramatic reduce the number of deaths from cancer. He and Jill Biden relaunched it last year.

The first lady frequently visits cancer research and treatment centers on her travels around the country to promote their work and encourage people to get screened. She also promotes the issue when she meets with spouses of global political leaders. In October, she launched a series of roundtables at a White House event with performer Mary J. Blige, and in November, she attended a World Series game in Philadelphia to help promote Major League Baseball's cancer initiative.