Gary Betty, chief executive officer of EarthLink, has cancer and has taken a leave of absence from the company.

EarthLink, a national Internet service provider, described Getty as having a “serious form of cancer” and said the disease “will require him to take an undetermined leave of absence from the company.”

Mike Lunsford, executive vice president of voice and access for EarthLink, will replace Betty on an interim basis. The company’s board named Lunsford to the post.

Betty, a graduate of Georgia Tech and a well-known executive in Atlanta, has worked for EarthLink since 1996. He joined the company after meeting Sky Dayton, the company’s founder. Betty is also a member of EarthLink’s board.

“I have known Gary since the early days of EarthLink,” Dayton said in a statement issued by EarthLink. “He has been a true leader and a major force in transforming the company from a small regional ISP into a national total communications provider serving millions of customers.

“Garry is a fierce competitor and has the determination to beat this disease,” he added. “Our thoughts and prayers are with him, his wife and his family.”

Dayton is now CEO of Helio, which is a joint wireless communications venture between EarthLink and SK Telecom. He also is a member of the EarthLink board.

Helio is one of the many projects EarthLink has undertaken under Berry’s leadership. The company also is involved in several municipal wireless broadband efforts and continues to expand its digital subscriber line offerings for people who want high-speed Internet access. EarthLink also recently acquired New Edge Networks through which it is expanding DSL coverage to 319 cities in 29 states.

Lunsford is also a veteran at EarthLink, having worked for the company since 1999. He directed the rollout of EarthLink’s broadband service.

Lunsford is a native of North Carolina and earned his Masters degree in business from the University of North Carolina at Chapel Hill.

EarthLink (NASDAQ: ELNK) shares traded at $6.69, up 2 cents, in afternoon trading.