If one had a lumpectomy with clear margins, no node involvment and is on anti-hormones, is it absolutely necessary to have radiation?

Discuss with doctor: Radiation decreases the likelihood of local recurrence in the affected breast. No patient is obligated to take any treatment, but, in the case of breast cancer, radiation will increase your chances of survival without recurrence. Women who have radiation are actually less likely to have local recurrence than are women who have simple mastectomy. A general surgery colleague may also want to answe.

Yes in most cases: It depends on both patients' and tumor's characteristics. For most early stage breast cancer, studies have shown that lumpectomy plus radiation is equivalent to mastectomy in term of long term survival. However, recent studies also showed that radiation can be safely omitted in elderly patients (70 or older) with hormonal receptor positive, node negative small breast tumor.

No: Not really there is enough data for a subset of patients specially who are over 70 have well diff tumor and have good margins that XRT can be avoided.