Former Empress Michiko underwent a successful breast cancer surgery Sunday at the University of Tokyo Hospital, the Imperial Household Agency said.

A lump was found in July in the 84-year-old former empress's left breast mammary gland during an echography exam and the cancer diagnosis was confirmed after a needle biopsy was conducted in early August.

Former Emperor Akihito and the couple's daughter Sayako Kuroda visited the hospital Sunday.

She had lost weight due to stress and a busy schedule amid the imperial succession earlier in the year, according to the agency. In June, she underwent cataract surgery on both of her eyes after being diagnosed with heart valve abnormalities, with the condition continuing to be monitored.

The former emperor became the first Japanese monarch to abdicate in about two centuries, bringing an end to the Heisei Era spanning his 30-year reign. His elder son Emperor Naruhito ascended the Chrysanthemum Throne on May 1.

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