The only data I know of on this specific subject comes from the subgroup analysis of the PRIME II trial, which randomly assigned patients to endocrine therapy alone or with radiation therapy. Its eligibility criteria included age 65 or older, tumor size 3 cm or smaller, grade 1 or 2, either grade 3 ...

While it is generally accepted that women with favorable early stage breast cancer over the age of 70 do not gain an overall survival advantage with adjuvant post-lumpectomy radiotherapy compared to taking adjuvant endocrine therapy, nearly 30% discontinue AI therapy within 2 years because of advers...