High-risk of recurrence for nodal micrometastasis with breast pathologic complete response (ypT0/Tis ypN1mi) after neoadjuvant chemotherapy.

Abstract

e12524 Background: Nodal micrometastatic disease (ypN1mic) after neoadjuvant chemotherapy (nCT) for breast cancer (BC) is considered an indication for axillary lymph node disection. While pN1mic prognostic impact has been extensively studied, the prognostic impact of ypN1mic disease is uncertain and these patients are usually grouped together with nodal macrometastatic disease. Since outcomes may be difficult to evaluate in the setting of BC residual disease, our aim was to compare the prognostic meaning of ypN1mic with that of ypN0 when a pCR is obtained in the breast. Methods: We retrospectively analyzed a series of 454 BC consecutive patients treated between 2010 and 2018 with neoadjuvant chemotherapy (nCT) based on anthracyclines and taxanes (plus antiHER2 treatment when appropriate). Pathologic complete response (pCR) was defined as ypT0/Tis ypN0. Patients with pre-nCT sentinel lymph node biopsy or without post-nCT pathologic evaluation were excluded. Disease free (DFS) and overall survival (OS) were analyzed with Kaplan-Meier curves and Cox regression models. Results: 454 BC patients were included, with 106 (24%) pCR. Median follow-up was 39 months. 99 (21.8%) patients obtained a pCR both in breast and axilla (ypT0/Tis ypN0), with 4 recurrences (4%) while only 7 (1.5%) patients had isolated nodal micrometastatic disease (ypT0/Tis ypN1mic), with 2 recurrences (28%). Median DFS was not reached for the ypN0 group and was 28 months (95%CI: 21.6-34.4 months) for the ypN1mic group (HR: 16.55, 95%cI: 2.68-102.37; p = 0.003). No differences were observed for OS (p = 0.77), although 2/2 ypN1mi showed distant recurrence (2/4 for ypN0 patients). Baseline clinical and pathologic characteristics were comparable between both groups, with no differences in performance status (p = 0.45), clinical nodal stage (p = 0.48), HER2 (p = 0.32), estrogen receptors (p = 0.93), grade (p = 0.34), presence of carcinoma in situ (0.60) or clinical complete response (p = 0.42). Clinical characteristics of patients with recurrence were also similar (100%: clinically positive nodes, negative estrogen receptors, no clinical complete response). Conclusions: Residual nodal micrometastatic disease after nCT seems to be associated with a higher risk of recurrence. Although longer follow-up and larger series are needed to confirm our data, these results support the escalation of post-nCT treatment even in patients with ypN1mic and breast pCR.