The first time a doctor mentioned there was a slight possibility that the strange bump on Katherine Mims's neck might be cancer, the 16-year-old high school junior was devastated. She went home and cried.

But then she did something that came naturally to the straight-A student: She hit the books.

"I just researched and researched," Mims recalled. Before long, she knew all about the thyroid and what it meant when the doctor said hers was enlarged. She knew the different types of thyroid cancer and had a sense of what treatment would involve. The knowledge was steadying.

Doctors recommended removing the lump quickly. They discovered during her surgery in November 2002 that it was, in fact, cancerous, and they removed Mims's thyroid. She underwent grueling radiation treatments the next January. She spent much of her junior year splitting time between class and medical appointments.

Mims, now 18, graduated from Potomac Falls High School yesterday, one of approximately 2,135 Loudoun students who received their diplomas last week and this week. She plans to take a year off and then attend Harvard University in 2005.

Her principal, E. Wayne Griffith, said Mims demonstrated some of her trademark qualities during her illness: perseverance and persistence.

"She's a wonderful young lady and very mature for her age," Griffith said. "I think she was an inspiration to others."

In the weeks between Mims's surgery and radiation treatments, her doctors advised her not to play on the school's volleyball team. But Mims -- who has also played basketball and run track in high school -- was determined. So play she did, against the advice of her doctors and even her parents.

"For Katherine, life is a negotiation," her father, Bill Mims, said with a laugh.

That would be state Sen. William C. Mims (R-Loudoun).

Mims was first elected to state office when Katherine was 5, and politics have been part of her life ever since. As a kindergartner, she begged to campaign door-to-door with her father during that first election. He let her but nixed her plan to split up and tackle houses individually, despite her impeccable 5-year-old logic that they would visit more people that way.

Being a state senator's daughter has not always been easy. In 2001, Mims spearheaded legislation that toughened teen driving laws in Virginia. He forgot to tell 15-year-old Katherine, who learned about it from a classmate. The classmate was not pleased. Katherine said she now thinks her father's push has made Virginia's roads safer, but both joke about those tense days.

There have been benefits, too. Katherine said she considers herself friends with some of the state's most powerful people. One day, Mims arrived to find his daughter in front of the computer. She looked up and said, "Senator Chichester says, 'Hi.' "

She had been instant messaging with Sen. John H. Chichester (R-Stafford), president pro tempore of the Virginia Senate and the author of a $3.9 billion tax plan that helped reshape this year's debate in Richmond on spending and taxes. It was Chichester's first time using the online technology, and Mims had to walk him through the process. When she was fighting cancer, she received flowers from many state legislators.

Mims said she plans to spend part of next year working in her father's senate office in Richmond. She also plans to spend time living with an aunt in Oregon and traveling abroad. She said that after 12 years in the classroom, she is looking forward to a year to learn outside it before Harvard. "I'm way more excited about doing this than I would be going to school in the fall," she said.

Mims had been planning to attend the Massachusetts Institute of Technology when a Harvard admissions officer called a few weeks ago with what he termed "a unique proposal": Take a year off and be guaranteed admission for the Class of 2009.

Feeling uneasy about her decision to attend the uber-techie university anyhow, Katherine accepted. She said she hoped to study medicine and perhaps become a doctor, maybe even an endocrinologist, a doctor that specializes in glands, including the thyroid.

Mims said her experiences have taught her just how much remains to be learned about how cancer works. For instance, her recent tests have showed conflicting results, which doctors cannot fully explain. Body scans have shown no evidence of cancer, but some of her blood tests have been more worrisome.

"It seems like there are so many things that people don't know," she said. "I'd like someone to fill in all the gaps."

Mims said her experience with the disease has put life in a sharp perspective. She has learned to better value the friends who visited constantly when she was sick and her family members who tended her needs.

"I know it sounds corny, but it helped me appreciate life," she said. "It really forces you to evaluate things and what you think is important."

Katherine Mims will be heading to Harvard University after a year of work and travel.