TOKYO - Japanese Emperor Akihito, who is having therapy to prevent prostate cancer returning, has celebrated his 77th birthday.

Japan's Emperor Akihito (3rd L) waves to well-wishers with Empress Michiko (3rd R), Crown Prince Naruhito (2nd L) and Crown Princess Masako (L) and Prince Akishino (2nd R) and his wife Princess Kiko as they celebrate the monarch's 77th birthday at the Imperial Palace in Tokyo Dec 23, 2010. [Photo/Agencies]

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Akihito greeted thousands of well-wishers on Thursday from a balcony at the Imperial Palace in Tokyo. The crowd waved Japanese flags.

The emperor underwent an operation for prostate cancer in 2003. The Imperial Household Agency says he has been undergoing hormonal therapy to prevent its recurrence.

Akihito has cut back official duties due to health reasons. He did not make any foreign trips this year.