Randy Pausch's new book, The Last Lecture, shot to number one on several online best-seller lists, including Amazon.com, after it was released last week. Pausch, a terminally-ill Carnegie Mellon computer science professor, became a national celebrity last year after a talk he gave became a viral video sensation.

In September, when Pausch delivered the lecture, he believed he had less than six months to live, a fact which added gravitas to the spirited, pithy address about the merits of perseverance. Pausch, it appears, takes his own advice. He has outlived his prognosis by more than two months and expects to keep fighting his pancreatic cancer.

"I've had spectacular medical care, and we're clawing for every extra month we can get," he wrote in an e-mail. "Realistically, I hope to get two to four more months."

The new book, which expands on the lessons of the lecture, is the culmination of Pausch's amazing rise to stardom beginning with a Wall Street Journal article covering his talk back in fall of 2007. Video from the session began to circulate on the Internet, and soon Pausch found himself on Oprah.

The new book, fittingly, was co-written by Jeffrey Zaslow, whose original article broke the professor's story. In November, they reportedly received an advance of close to $7 million from Hyperion, a division of Disney.

Pausch was originally diagnosed with pancreatic cancer during the summer of 2006. After extensive chemotherapy and radiation, it appeared the cancer might be in remission, but it returned in August 2007, spreading to his liver and spleen, leading doctors to tell Pausch he had between three and six months to live. Since then, he's been receiving palliative treatments.

Pausch tracks his experience with cancer with startling honesty on a day-to-day updates web page. He is optimistic but unswervingly realistic. In March, recovering from a brief hospitalization, he wrote, "The really good news is that ... the tumors are being very chivalrous and not taking advantage of this opportunity to run wild, before I'm strong enough to fight back."

Last week, Pausch qualified for a new treatment known as SIR-Spheres, in which tiny radioactive pellets are directly injected into his liver. Approved by the FDA in 2002, it's not generally considered a cure, but it could extend his life.

"New treatments are always arriving, so although the odds are long,

I remain optimistic new stuff will arrive just in time," he told

Wired.com.

As for his book's runaway success, the longtime professor's hopes for the book have already been fulfilled.

"While everybody seems to be focused on the number of copies, I really only cared about the first three, which will go to my kids,"

said Pausch. "I've said my piece – my time now is entirely focused on family."