The condition is curable, Dimon said in a memo to shareholders and employees, and he will undergo radiation and chemotherapy treatment for about eight weeks.

During that time, Dimon said his business travel would be limited but he would "be able to continue to be actively involved in our business."

JPMorgan's shares fell the most of any of the 24 stocks in the KBW index of bank stocks. The stock was down more than 1 percent at $56.90 in midday trading.

Rafferty Capital Markets bank analyst Dick Bove said in a report Wednesday Dimon was unlikely to retain his chairman title when he returns from treatment, and would likely spread more of his daily duties among other executives at the bank.

"JPMorgan Chase simply cannot present itself to the world as if it were a one-man show," Bove wrote.

Sources have previously said the bank has many senior executives who could step into Dimon’s role if needed.

Potential internal successors include the head of the corporate and investment bank, Daniel Pinto; chief operating officer, Matt Zames; consumer banking head, Gordon Smith and asset management chief, Mary Erdoes. The bank has a short-, medium- and long-term succession plan in place, a source told Reuters on Tuesday.

JPMorgan lead director Lee Raymond said at the bank's shareholder meeting in May last year that the board intended to have a viable successor to Dimon but he hoped Dimon would stay at JPMorgan far into the future.

"I have no illusions that we will be able to clone Jamie," Raymond said at the time.

According to the National Cancer Institute, the survival rate for mouth and throat cancers diagnosed at any stage is 63 percent after five years. "I feel very good now and will let all of you know if my health situation changes," Dimon said in his memo.

Dimon has been JPMorgan’s chief executive since 2006. He arrived at the bank via its 2004 merger with Bank One Corporation, where he had been chairman and CEO.

(Reporting by Peter Rudegeair; Editing by Bernadette Baum)