Former Empress Michiko, who was diagnosed with early-stage breast cancer last month, will have surgery on Sunday at the University of Tokyo Hospital, the Imperial Household Agency said Tuesday.

The 84-year-old will be admitted to hospital on Saturday for surgery. A lump was found in July in her left breast's mammary gland during an echography exam and the cancer diagnosis was confirmed after a needle biopsy was conducted on Aug. 2.

The former empress had a rest in Karuizawa, Nagano Prefecture, and Kusatsu in Gunma Prefecture late last month with her husband, former Emperor Akihito, who abdicated at the end of April.

She had lost weight due to stress and a busy schedule due to the imperial succession, 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.

Former Emperor Akihito 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.