LONDON, Nov 28 (Reuters) - Barclays PLC said on Monday that Chief Executive C.S. Venkatakrishnan would undergo treatment for non-Hodgkin lymphoma, a type of cancer, adding that the condition is treatable and that he would keep working when possible.

The CEO, known inside the British bank as Venkat, said in a regulatory filing that doctors have said his prognosis is "excellent", with the treatment in New York expected to last 12 to 16 weeks.

Barclays has not appointed an interim chief executive, with Venkat and the lender's executive committee expected to continue running the company, said a spokesperson for the bank.

"During this period, the company will run normally, and I will continue to be actively engaged in managing it," Venkatakrishnan said in the filing.

Non-Hodgkin lymphoma is a cancer that develops in the lymphatic system, weakening the immune system, but most cases are considered "very treatable" according to information on the website of Britain's National Health Service.

Venkat, who is a U.S. citizen, may have to cut back on public engagements, such as a scheduled appearance at the World Economic Forum meetings in Davos next January, according to Barclays' spokesperson.

A former JPMorgan banker, Venkatakrishnan has endured a difficult first year in charge of Barclays since taking over from Jes Staley last November.

Barclays' strong investment banking results amid volatile markets have been overshadowed by an administrative blunder that saw it sell more securities in the United States than it was permitted to, leading to regulatory penalties and hefty losses.

Venkatakrishnan, who oversaw risk at the bank before taking on the top job, has called the error "preventable" and sought to reassure investors that investments in better controls mean a repeat will not happen.

Last month the bank beat analysts' expectations with a small rise in third quarter profit, but faces a tough economic outlook in its home market as the British economy shrinks and inflation rises.

Barclays shares were up 0.5% on Monday, against a broader FTSE 100 index down 0.5%. (Reporting by Lawrence White in London and Sinchita Mitra in Bengaluru; Editing by Sherry Jacob-Phillips, Kirsten Donovan and Susan Fenton)