Empress Emerita Michiko will undergo surgery for breast cancer, the Imperial Household Agency announced Friday. It said the cancer is still at an early stage.

According to the agency, a “tumorous mass” was found in her left breast during tissue testing at the Imperial Household Agency Hospital last month. She won’t undergo surgery until at least September.

The 84-year-old former empress has been experiencing shortness of breath more frequently during morning walks since the beginning of the year, the agency said earlier.

In June, she was diagnosed with heart abnormalities, prompting doctors to call for her daily physical burden to be reduced. Later the same month, she had cataract surgery performed on both eyes after complaining of vision difficulties for several years.

The agency did not administer treatment for the heart problems as her symptoms are relatively mild, it said, though she has also been diagnosed with an irregular heartbeat and higher risk of heart failure.

The former empress retired from her official duties when then-Emperor Akihito abdicated at the end of April after three decades on the Chrysanthemum Throne.