CALGB 9343 evaluated whether women aged 70 years or older with stage I, estrogen receptor-positive breast cancer could safely omit whole-breast radiotherapy after lumpectomy when treated with endocrine therapy. The randomized study compared tamoxifen alone with tamoxifen plus radiotherapy. Long-term follow-up showed that radiotherapy reduced local recurrence, but there was no meaningful difference in overall survival. These findings helped define a group of older women in whom avoiding radiotherapy can be reasonable when the priority is minimizing treatment burden and the expected absolute benefit of radiation is small. For surgeons, the trial illustrates that local therapy should be individualized according to tumour biology, age, life expectancy, comorbidities and patient preference. Breast-conserving surgery remains effective, but the intensity of adjuvant local treatment can be adjusted when the risk of recurrence is low. The practical message is not that radiotherapy is unnecessary for older patients. Rather, some carefully selected women may reasonably choose a less intensive postoperative pathway after discussion of the trade-off between slightly higher local recurrence risk and avoidance of radiation. CALGB 9343 remains a foundational study in the broader movement toward personalized, less burdensome breast cancer treatment.