Microscopic extracapsular extension in the axilla: is this an indication for axillary radiotherapy?

Although the axilla is often treated with radiotherapy (RT) postoperatively when microscopic extracapsular extension (ECE) of lymph nodal metastases is present, little data are available to assess axillary failure in the absence of such treatment. As it has been the practice at this institution to withhold axillary irradiation in the presence of microscopic extracapsular spread, we retrospectively analyzed our results for axillary recurrence, disease-free survival (DFS), and overall survival (OS).

Clinical records were reviewed of 82 women with Stage II node positive breast cancer treated with lumpectomy, axillary dissection, and RT in addition to systemic chemo/hormonal therapy. Axillary surgery consisted of a level I, II, +/- III dissection, with a median of 16.5 nodes removed. Tangential radiotherapy fields were used to treat the breast. All patients were also treated with an abbreviated supraclavicular field with the lateral border medial to the humeral head. Pathological sections were available for review in 72 of the 82 women.

Twenty-seven of 72 (37.5%) had evidence of ECE; 45 of 72 (62.5%) had metastatic carcinoma confined within the nodal capsule. Clinical characteristics were comparable between the patients with and without ECE with the exception of (a) pathologic subtype, with a greater percentage of infiltrating ductal tumors associated with ECE (p = 0.044), and (b) number of positive lymph nodes, with 93% of patients without ECE having one to three positive nodes vs. only 56% among patients with ECE (p < 0.001). With a median follow-up of 40 months, 1 of 27 patients (4%) with ECE experienced an axillary failure as a component of first failure compared to 0 of 45 patients without ECE (p = 0.4). There were no isolated axillary failures. Five-year disease-free survival (72% without ECE vs. 57% with ECE, p = 0.12) and overall survival (83% vs. 53%, respectively, p = 0.068) suggested a less favorable outcome for patients with ECE.

Microscopic ECE appears to be associated with increased axillary involvement and decreased survival rather than subsequent axillary failure. Our data suggest that radiotherapy to a dissected axilla may be omitted for the sole indication of microscopic extracapsular disease.