The powerful chairman and chief executive of JPMorgan Chase, Jamie Dimon, announced in a letter to shareholders Tuesday that he has throat cancer and is about to begin treatment. Dimon, 58, said the doctors found it before it had spread beyond the “original site” and the lymph nodes on the right side of his neck. It is curable, he said. The letter came on Dimon’s 10-year anniversary as CEO. In the aftermath of the financial crisis, many pointed to Dimon as a hero as his bank emerged relatively unscathed. However, in the subsequent years JPMorgan has faced multibillion-dollar settlements over shady sales of mortgage-backed securities, the Bernard Madoff Ponzi scheme, and the so-called London Whale controversy.