Forty-five studies were included in the review (n=23,357 patients; 18,878 treated with external beam radiation therapy). Thirty studies reported on individual patients with axillary recurrence; these were included in the L'Abbe plot. Median follow-up ranged from 15 to 102 months.
Axillary recurrence after negative sentinel lymph node biopsy was identified in 127 patients (0.5%), of whom 73 had received external beam radiation therapy as part of their initial treatment. The median interval between sentinel lymph node biopsy and detection of axillary recurrence was 22 months (73 patients).
Of patients that received adjuvant therapy (2,286 chemotherapy and 3,197 hormone treatment), 28 developed axillary recurrence (including eight on chemotherapy and 14 on hormone therapy).
In pooled analysis, external beam radiation therapy was associated with a lower rate of axillary recurrence including intraoperative radiotherapy as external beam radiation therapy (OR 0.32, 95% CI 0.17 to 0.59), and excluding intraoperative radiotherapy as external beam radiation therapy (OR 0.29, 95% CI 0.16 to 0.55). Heterogeneity was found (variation between studies was 72%), but this was not statistically significant (p=0.33).
In a subgroup analysis based on length of follow-up, a clear effect on axillary recurrence was found for patients treated with external beam radiation therapy to the breast after 60 months (five studies) without evidence of statistical heterogeneity; significant heterogeneity was found for all other groups.