First lady Laura Bush had a skin cancer tumor removed from her right shin in early November but decided it was a private matter and did not reveal it publicly.

The White House acknowledged the procedure Monday night after Mrs. Bush was noticed with a bandage below her right knee.

The cancer was a squamous cell carcinoma, the second most common form of skin cancer, said Susan Whitson, her press secretary.

A squamous cell carcinoma is a tumor that affects the middle layer of the skin. It is more aggressive than basal cell cancer, the most common form of skin cancer. Squamous cell cancer is more likely than basal cell cancer to spread to other locations, so patients need to have lymph nodes in the region near the tumor routinely examined, according to the National Cancer Institute’s Web site.

More than 1 million cases of basal and squamous cell skin cancers are diagnosed annually, according to the American Cancer Society, which says that most but not all of these forms of skin cancer are highly curable.

Explaining why the procedure was not disclosed until now, Whitson said, “This medical procedure was a private matter for Mrs. Bush, but when asked by the media today, we answered the question.”

The first lady was noted wearing a bandage on her right leg before the election. At the time Whitson said Mrs. Bush had a sore on her shin.

In late October, Mrs. Bush had a biopsy because the sore was not healing, Whitson said, and it was determined to be a squamous cell carcinoma.

Whitson said Mrs. Bush’s tumor was removed under a local anesthetic. She called it “a little surgical procedure. It’s no big deal. She detected it early. She caught it early.” No further treatment was needed.

Whitson said the patch was about the size of a nickel and became a matter of concern just before Election Day, Nov. 7.

“It’s healing fine and it has not interrupted her schedule at all,” Whitson said. In the same month she had the operation, Mrs. Bush accompanied her husband on a trip to Singapore and Vietnam.

In 2001, President Bush had four lesions removed from his face, including two caused by a common skin ailment that can lead to cancer if left untreated. None of the four were cancerous, the White House said.

People with fair skin and prolonged sun exposure are more likely to develop squamous cell carcinoma, and it is more common in the southern latitudes of the northern hemisphere. Mrs. Bush is from Texas.

Squamous cell carcinoma shouldn’t be confused with melanoma, the most dangerous form of skin cancer. Together, basal and squamous cell carcinoma are responsible for less than 0.1 percent of cancer deaths, while the American Cancer Society estimates almost 8,000 Americans will die from melanoma this year.

Monday’s revelation was the second case this year of a belated White House announcement. In February, the White House waited almost a day before disclosing that Vice President Dick Cheney had shot a fellow hunter during a quail-hunting trip.