The Absolute Effect / Evidence / CALGB 9343
Breast Cancer · Radiation Oncology · RT Omission

CALGB 9343

Clinical question

In women ≥70 with T1N0 ER-positive breast cancer after lumpectomy and endocrine therapy, can RT be omitted?

Trial context
Population
636 women ≥70 years, T1N0M0, ER-positive breast cancer
Intervention
Tamoxifen + RT vs tamoxifen alone after lumpectomy
Key endpoint
10-year freedom from locoregional recurrence
Time horizon / follow-up
10 years
Absolute Effect

What changes for patients?

RT reduced 10-year locoregional recurrence from about 10% to 2%, an absolute reduction of 8 percentage points (NNT 13). There was no significant difference in distant metastasis, breast-cancer-specific survival or overall survival. NNT is based on 10-year freedom from locoregional recurrence.

NNT: 13

Treatment burden / harm

RT-related toxicity

NNH: Not quantifiable from the reported endpoint; toxicity described in text

Relative effect

HR: 0.18

95% CI 0.07–0.42

Clinical interpretation

The patient-level trade-off is more local recurrence without radiotherapy but no demonstrated survival difference in selected older women taking endocrine therapy.

Primary publication

← Return to The Absolute Effect

Current-practice context · reviewed 14 October 2026

For women aged 70 years or older with small, node-negative ER-positive breast cancer who will take endocrine therapy, omission of breast RT can be reasonable after shared decision-making. The trade-off is higher ipsilateral/local recurrence without a demonstrated overall-survival difference; age alone is insufficient without considering tumour risk, life expectancy, endocrine-therapy adherence and patient priorities.

CALGB 9343 primary/long-term report ↗ · Current guideline guidance ↗