# PRIME II

Source: https://onco.cc/trials/prime-ii/  
OnCo record `prime-ii` (Trial). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

PRIME II confirmed in a larger and more recent population that omitting radiotherapy in older women with low-risk hormone-sensitive breast cancer raises local recurrence modestly without affecting survival.

## Summary

PRIME II randomised 1,326 women aged 65 or older with hormone receptor-positive, node-negative breast cancers up to 3 cm, treated by breast-conserving surgery and endocrine therapy, to radiotherapy or none. Ten-year local recurrence was 9.5 percent without radiotherapy and 0.9 percent with it; distant recurrence, breast cancer-specific and overall survival did not differ (Kunkler and colleagues, Lancet Oncology 2015 and New England Journal of Medicine 2023).

## Fields

- Kind: Trial
- Status: positive
- Last checked: 2026-09-16
- Tags: radiation-wave2
- Phase: 3
- Setting: Women aged 65 or over with low-risk hormone receptor-positive breast cancer after breast-conserving surgery: endocrine therapy with or without whole-breast radiotherapy
- Sponsor: University of Edinburgh
- Enrolled: 1326
- Result: 10-year local recurrence 9.5% (no radiotherapy) vs 0.9% (radiotherapy); no difference in survival.
- Outcomes: Ipsilateral breast tumour recurrence at 10 years: Endocrine therapy alone 9.5% vs Endocrine therapy plus radiotherapy 0.9%

## Sources

- ISRCTN95889329: https://www.isrctn.com/ISRCTN95889329
- NEJM 2023: https://doi.org/10.1056/NEJMoa2207586

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- technologies: [Active surveillance](https://onco.cc/technologies/active-surveillance/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/)

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