Introduction and Study Design For patients (pts) with a metastatic sentinel node (SN), axillary dissection is standard treatment to achieve optimal locoregional control. However, for many pts the SN is the only positive node and for pts with minimal SN involvement, axillary dissection (AD) may be overtreatment. IBCSG Trial 23-01 was designed to determine whether AD is necessary in pts with minimal SN involvement (defined as one or more micrometastatic (≤2 mm) SNs) and tumor ≤5 cm. Consenting eligible pts were first registered; those with the requisite SN involvement were randomized to AD (group A) vs. no further axillary surgery (group B). The primary endpoint was disease-free survival (DFS). Secondary endpoints included overall survival (OS) and systemic disease-free survival (SDFS). The trial started in April 2001 and closed in February 2010. The accrual target was 1,960 pts to provide 90% power to detect non-equivalence if 5-year DFS was 64% for group B and 70% in group A. At closure 6,681 pts had been registered, with 934 randomized from 27 centers. The primary reasons for early closure were that projected time to complete accrual was too long, and the aggregate event rate at 30 months median follow up was much lower than anticipated. Baseline Characteristics and Treatment Mean patient age at entry was 54 years (range 26–81). More postmenopausal (56%) than premenopausal pts (44%) were randomized. Sixty-seven percent of pts had tumor <2 cm, while 7% had tumor ≥3 cm; 26% had grade 3 disease. Tumors were estrogen-receptor positive in 89% of pts, and progesterone-receptor positive in 75%. In the involved sentinel node(s), 67% of pts had ≤1.0 mm micrometastasis, 29% had 1.1−2.0 mm micrometastasis, 2% had metastasis >2.0 mm, and 2% were unknown. Most (96%) pts underwent lymphoscintigraphy, and 1 or 2 sentinel nodes were found in about 85%. A previous excision biopsy was performed in 16%. Conservative surgery was definitive treatment in 75%; the others received mastectomy. Adjuvant radiotherapy was performed in 89% of group A and 92% of group B. Outcomes On 25 May 2011, median follow was 49 months. There were 88 DFS events. Sites of first DFS event were breast cancer-related in 66 pts [local (8), contralateral breast (10), regional (6), and distant (42)], and non-breast cancer-related in 22 [second malignancies (17) and deaths without prior cancer event (5)]. Four-year DFS (± standard error) was 91% (±1.4%). Four-year competing risk cumulative incidences were 7.3% (±1.0%) for breast cancer events and 2.0% (±0.5%) for non-breast cancer events. With 101 DFS events, the trial is estimated to have 90% power to detect non-equivalence if 5-year DFS is 87% for group B compared with 92% for group A. Conclusion In this trial, restricted to clinically N0 with microscopic SN involvement, breast cancer recurrence and relapse rates are very low at a median follow-up of 4 years. The first comparison of outcomes between the two arms will be presented after a median follow-up of 5 years, when number of DFS events is anticipated to exceed 100. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr S3-1.

BACKGROUND: The phase III IBCSG 23-01 multicenter, randomized, non-inferiority trial compared disease-free survival (DFS) in breast cancer patients with one or more micrometastatic (≤2 mm) sentinel nodes (SNs) randomized to either axillary dissection (AD) or no axillary dissection (no-AD). Results after 5 years showed no difference in DFS between the arms. Here we report results after a median follow-up of 9.8 years. METHODS: Eligible patients had cancers of pathological diameter ≤5 cm and one or more micrometastatic (≤2 mm) foci, including isolated tumor cells, in the SNs. Patients with axillary macrometastases were excluded. Breast surgery was conservative or mastectomy. Eligible patients were randomized to AD vs. no-AD. The primary endpoint was disease-free survival (DFS); secondary endpoints were overall survival (OS), site of recurrence (particularly axillary recurrence), and surgical complications of AD. DFS and OS were estimated using the product-limit method, and the log-rank test was used to compare the treatment groups. Patients without a DFS or OS event were censored at the date of last follow-up. Non-inferiority margin for no-AD vs. AD was defined as a DFS hazard ratio (HR, no-AD relative to AD) of <1.25, and was assessed using a z-test applied to the log HR. Active follow-up of patients was terminated in February 2017. RESULTS: From 2001 to 2010, 934 patients were randomized at 27 centers; 931 were evaluable (467 in the no-AD group and 464 in the AD group). Median follow-up was 9.8 (IQR: 7.8–12.7) years. The number and types of first DFS events according to treatment group are shown in the Table. Disease-free Survival EventsNo-ADADTotal101117Breast cancer related events7475Local1413Contralateral breast1012Regional [ipsilateral axillary events]9 [8]3 [2]Distant4147Non-breast cancer related events2742Second malignancies1723Death without prior cancer event62Death with unknown cancer status417 10-year DFS was 75% (95% confidence interval [CI]: 72%–81%) in the no-AD group and 75% (95% CI: 71%–79%) in the AD group (HR [no-AD vs. AD]=0.85; 95% CI: 0.65–1.11; log-rank p=0.23; non-inferiority p=0.002). There were 45 deaths in the no-AD group and 58 in the AD group. 10-year OS was 91% (95% CI: 88%–94%) in the no-AD group and 88% (95% CI: 85%–92%) in the AD group (HR [no-AD vs. AD]=0.77; 95% CI: 0.56–1.07; log-rank p=0.19). CONCLUSION: Findings after a median follow-up of 9.8 years fully support the findings at 5 years in that no-AD is not inferior to AD with respect to DFS, and there is no significant difference between the arms for DFS and OS, thus confirming that AD is not indicated in patients with micrometastatic SNs. Citation Format: Galimberti V, Cole BF, Viale G, Veronesi P, Vicini E, Intra M, Mazzarol G, Massarut S, Zgajnar J, Taffurelli M, Littlejohn D, Egli T, Tondini C, Di Leo A, Colleoni M, Regan MM, Coates AS, Gelber RD, Goldhirsch A. Axillary dissection vs. no axillary dissection in patients with cT1-T2cN0M0 breast cancer and only micrometastases in the sentinel node(s): Ten-year results of the IBCSG 23-01 trial [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS5-02.

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