Based on this favorable rate, we concluded that patients aged 65 years or older with both estrogen and progesterone receptor-positive breast cancer of 3 cm or smaller by palpation, who underwent breast-conserving surgery, had histologically negative margins judged by the “5-mm interval slice and 5-mm margin-free” method and no lymphatic invasion around the tumor do not need radiotherapy. Here, PGR is linked to breast cancer.