International journal of radiation oncology, biology, physics 2005-07-15
Locoregional recurrence rates and prognostic factors for failure in node-negative patients treated with mastectomy: implications for postmastectomy radiation.   
Postmastectomy radiation therapy (PMRT) reduces locoregional recurrence (LRR) of breast cancer. Survival appears improved in patients at higher risk for LRR. This study addresses whether subsets of node-negative patients with sufficiently high risk of LRR might benefit from PMRT.
Retrospective analysis of a cohort of 877 cases of node-negative breast cancer treated with mastectomy, without adjuvant radiation, from 1980 to 2000.
Median follow-up was 100 months. Ten-year cumulative incidence of LRR as first event was 6.0%. Size greater than 2 cm, margin less than 2 mm, premenopausal status, and lymphovascular invasion (LVI) were independently significant prognostic factors. Ten-year LRR was 1.2% for those with 0 risk factors, 10.0% for those with 1 risk factor, 17.9% for those with 2 risk factors, and 40.6% for those with 3 risk factors. The chest wall was the site of failure in 80% of patients.
Postmastectomy radiation therapy has not been recommended for node-negative patients because the LRR rate is low in that population overall. This study suggests, however, that node-negative patients with multiple risk factors, including close margins, T2 or larger tumors, premenopausal status, and LVI, are at higher risk for LRR and might benefit from PMRT. Because the chest wall is the most common site of failure, treating the chest wall alone in these patients to minimize toxicity is reasonable.

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