Do you hold endocrine therapy during adjuvant breast radiotherapy?

I start endocrine therapy after RT. For one, I don’t think there is a rush to get endocrine therapy going and would rather focus on the patient being able to tolerate it for the long term. And two, if radiation works best on quickly dividing cells, I don’t want to stunt their proliferation (which we know happens based on studies looking at Ki-67 before and after endocrine therapy) until after RT is completed.

No, we don’t hold endocrine during RT as data suggests no difference in toxicity or local control.

The only exception is CD4/6 inhibitor which is now standard for high-risk node positive patients where we start the medication after RT.

There is no data that shows a detriment to holding endocrine therapy in all the NSABP studies. Theoretically, you would reduce cycling. Recurrences are so few that it would be hard to prove a detriment. I remember reading a mouse article that suggested a higher risk of pneumonitis with concurrent tamoxifen so I held it (I’ll never be able to find that article now).

We see our patients regularly and hear complaints. Several blamed their hormonal issues on radiation. Since there is no benefit, I d...

If an aromatase inhibitor, I start concomitant with radiation, no reason to wait. Tamoxifen elicits more negative reactions from our radiation oncology colleagues, so I typically wait after, especially if it’s a short course of radiation.

Remember that in many patients with ER-positive breast cancer, after diagnosis, surgery, and chemotherapy, endocrine therapy, arguably the backbone treatment, is still waiting on everyone to finish.

Judgement is important as pertains to the risk and remember ...

Standard of care with adjuvant breast therapy has been adjuvant chemotherapy followed by adjuvant radiation and hormonal therapy. Radiotherapy concurrent with endocrine therapy didn't increase or decrease either the incidence of radiation-induced toxicity or the survival rate compared with that of the sequential group. (Li et al., PMID 27054754) In a systematic review, studies evaluated the timing of adjuvant radiation, tamoxifen (5 studies, 1,550 patients), or aromatase inhibitors (6 studies, 6...

1. Yes, it is important to avoid concurrent toxicity and watch the patient closely; if there are adverse effects, hold till radiation is completed.
2. I was concerned about the cytostatic effects, shown in concurrent chemotherapy + adj endocrine Rx trials, so still some concerns there.