Single-Cell Map of Diverse Immune Phenotypes in the Breast Tumor Microenvironment.

Knowledge of immune cell phenotypes in the tumor microenvironment is essential for understanding mechanisms of cancer progression and immunotherapy response. We profiled 45,000 immune cells from eight breast carcinomas, as well as matched normal breast tissue, blood, and lymph nodes, using single-cell RNA-seq. We developed a preprocessing pipeline, SEQC, and a Bayesian clustering and normalization method, Biscuit, to address computational challenges inherent to single-cell data. Despite significant similarity between normal and tumor tissue-resident immune cells, we observed continuous phenotypic expansions specific to the tumor microenvironment. Analysis of paired single-cell RNA and T cell receptor (TCR) sequencing data from 27,000 additional T cells revealed the combinatorial impact of TCR utilization on phenotypic diversity. Our results support a model of continuous activation in T cells and do not comport with the macrophage polarization model in cancer. Our results have important implications for characterizing tumor-infiltrating immune cells.

Regulatory T Cells Exhibit Distinct Features in Human Breast Cancer.

Regulatory T (Treg) cells reside in lymphoid organs and barrier tissues where they control different types of inflammatory responses. Treg cells are also found in human cancers, and studies in animal models suggest that they contribute to cancer progression. However, properties of human intratumoral Treg cells and those present in corresponding normal tissue remain largely unknown. Here, we analyzed features of Treg cells in untreated human breast carcinomas, normal mammary gland, and peripheral blood. Tumor-resident Treg cells were potently suppressive and their gene-expression pattern resembled that of normal breast tissue, but not of activated peripheral blood Treg cells. Nevertheless, a number of cytokine and chemokine receptor genes, most notably CCR8, were upregulated in tumor-resident Treg cells in comparison to normal tissue-resident ones. Our studies suggest that targeting CCR8 for the depletion of tumor-resident Treg cells might represent a promising immunotherapeutic approach for the treatment of breast cancer.

Tumor resident regulatory T cells.

The immune system mediates powerful effector mechanisms to protect against a diversity of pathogens and equally as important regulatory functions, to limit collateral damage of inflammation, prevent misguided immune responses to "self", and promote tissue repair. Inadequate regulatory control can lead to a variety of inflammatory disorders including autoimmunity, metabolic syndrome, allergies, and progression of malignancies. Cancers evolve complex mechanisms to thwart immune eradication including coopting normal host regulatory processes. This is most evident in the analysis of tumor infiltrating lymphocytes (TILs), where a preponderance of immunosuppressive immune cells, such as regulatory T (Treg) cells are found. Treg cells express the X-chromosome linked transcription factor Foxp3 and play a crucial role in maintaining immune homeostasis by suppressing inflammatory responses in diverse biological settings. Treg cells in the tumor microenvironment promote tumor development and progression by dampening anti-tumor immune responses, directly supporting the survival of transformed cells through elaboration of growth factors, and interacting with accessory cells in tumors such as fibroblasts and endothelial cells. Current insights into the phenotype and function of tumor associated Treg cells have opened up opportunities for their selective targeting in cancer with the goal of alleviating their suppression of anti-tumor immune responses while maintaining overall immune homeostasis. Here, we review Treg cell biology in the context of the tumor microenvironment (TME), and the important role they play in cancer immunotherapy.

Surgical Management and Long-Term Outcomes of BIA-ALCL: A Multidisciplinary Approach.

BACKGROUND: Breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) is a subtype of ALCL that arises as a seroma or a mass in the capsule surrounding textured breast implants. However, collections of cases usually come from large groups of institutions or countries, with different approaches regarding surgery and treatment. Here we describe a cohort of 18 cases undergoing implant removal and capsulectomy followed at Memorial Sloan Kettering Cancer Center (MSKCC). PATIENTS AND METHODS: We retrospectively analyzed all the cases of women with breast implants undergoing implant removal and capsulectomy for BIA-ALCL at MSKCC from January 2011 to June 2020. RESULTS: Median age at diagnosis was 57 (range 35-77) years following a median implant exposure of 11 (range 7-33) years. All known implants were macrotextured with the proprietary Biocell macrotexturing pattern from salt-loss technique. A total of 16 patients (89%) had implants placed for breast cancer reconstruction. Patients presented with clinically evident effusion in 78% of cases and a mass in 17% of cases, and 83% of patients presented with stage 1 BIA-ALCL. Patients were followed for a median of 43.4 months (SD 45 months) after diagnosis. There were no cases of recurrent ALCL. All patients remain disease free and no patients died of ALCL. CONCLUSIONS: In this cohort of patients with BIA-ALCL surgically treated and followed at a single institution, we confirm the importance of adequate surgery (bilateral implant removal and complete capsulectomy) in patients presenting with seroma-confined disease. This dataset reinforces high rates of progression-free and overall survival when diagnosis is identified and treatment performed in those with limited-stage disease.

Impact of Neoadjuvant Chemoimmunotherapy on Surgical Outcomes and Time to Radiation in Triple-Negative Breast Cancer.

BACKGROUND: We examined the association between immunotherapy-containing and standard chemotherapy regimens with treatment delays and postoperative complications in stage II-III triple-negative breast cancer. The effect of immune-related adverse events (irAEs) was compared. PATIENTS AND METHODS: We compared 139 women treated with neoadjuvant pembrolizumab plus chemotherapy (KEYNOTE-522 regimen) from August 2021 to September 2022 with 287 consecutive patients who received neoadjuvant chemotherapy alone prior to July 2021 and underwent surgery. Baseline characteristics, time to treatments, and surgical complications were compared using two-sample non-parametric tests. Linear regression evaluated association of irAEs with time to surgery and radiation. Logistic regression identified factors associated with surgical complications. RESULTS: Age, body mass index, race, American Society of Anesthesiologists (ASA) class, and mastectomy rates were similar among cohorts. No clinically relevant difference in time from end of neoadjuvant treatment to surgery was observed [KEYNOTE-522: median 32 (IQR 27, 43) days; non-KEYNOTE-522: median 31 (IQR 26, 37) days; P = 0.048]. Time to radiation did not differ (P = 0.7). A total of 26 patients (9%; non-KEYNOTE-522) versus 11 (8%; KEYNOTE-522) experienced postoperative complications (P = 0.6). In the KEYNOTE-522 cohort, 59 (43%) of 137 patients experienced 82 irAEs; 40 (68%) required treatment. Older age (P = 0.018) and ASA class 4 (P = 0.007) were associated with delays to surgery after adjusting for clinical factors. Experiencing ≥ 1 irAE was associated with delay to radiation (P = 0.029). IrAEs were not associated with surgical complications (P = 0.4). CONCLUSIONS: We observed no clinically meaningful difference between times to surgery/adjuvant radiation or postoperative complications and type of preoperative chemotherapy. IrAEs were associated with delay to adjuvant radiation but not with postoperative complications or delay to surgery.

Does Non-Classic Lobular Carcinoma In Situ at the Lumpectomy Margin Increase Local Recurrence?

BACKGROUND: The clinical significance of nonclassic, lobular carcinoma in situ (NC-LCIS) at the surgical margin of excisions for invasive cancer is unknown. We sought to determine whether NC-LCIS at or near the margin in the setting of a concurrent invasive carcinoma is associated with risk of ipsilateral breast tumor recurrence (IBTR) and locoregional recurrence (LRR). METHODS: Patients with stage 0-III breast cancer and NC-LCIS who underwent lumpectomy between January 2010 and January 2022 at a single institution were retrospectively identified. NC-LCIS margins were stratified as <2 mm, ≥2 mm, or within shave margin. Rates of IBTR and LRR were examined. RESULTS: A total of 511 female patients (median age 60 years [interquartile range (IQR) 52-69]) with NC-LCIS and an associated ipsilateral breast cancer with a median follow-up of 3.4 years (IQR 2.0-5.9) were identified. Final margins for NC-LCIS were ≥2 mm in 348 patients (68%), <2 mm in 37 (7.2%), and within shave margin in 126 (24.6%). Crude incidence of IBTR was 3.3% (n = 17) and that of LRR was 4.9% (n = 25). There was no difference in the crude rate of IBTR by NC-LCIS margin status (IBTR rate: 3.7% ≥2 mm, 0% <2 mm, 3.2% within shave margin, p = 0.8) nor in LRR (LRR rate: 4.9% ≥2 mm, 2.7% <2 mm, 5.6% within shave margin, p = 0.9). CONCLUSIONS: For completely excised invasive breast cancers associated with NC-LCIS, extent of margin width for NC-LCIS was not associated with a difference in IBTR or LRR. These data suggest that the decision to perform reexcision of margin after lumpectomy should be driven by the invasive cancer, rather than the NC-LCIS margin.

Axillary Downstaging in Occult Primary Breast Cancer After Neoadjuvant Chemotherapy.

BACKGROUND: Neoadjuvant chemotherapy (NAC) is increasingly used for clinically node-positive (cN+) tumors with intact primary breast cancer (IPBC) to downstage the axilla, and those who convert to cN0 may be eligible for sentinel lymph node biopsy (SLNB). Rates of axillary downstaging in occult primary breast cancer (OPBC) are unknown. OBJECTIVE: The aim of this study was to determine the frequency of nodal pathologic complete response (pCR) following NAC in a cohort of patients with OPBC. METHODS: Twenty-eight patients with stage II/III OPBC treated between January 2008 and December 2019 were identified. Twenty patients had cN1-3 OPBC, pretreatment lymph node needle biopsy, and received NAC; these constituted the study population. Treatment factors and nodal pCR rates were summarized by tumor subtype. RESULTS: Median age at diagnosis was 54 years. Most patients presented with cN1 disease (75%) and ductal histology (80%). Nodal pCR was seen in 16/20 (80%) patients. Eight (40%) patients were triple negative, 6 (30%) were estrogen receptor-positive/human epidermal growth factor receptor 2-negative (ER +/HER2 -), and 6 (30%) were HER2 positive, with pCR rates of 88%, 50%, and 100%, respectively. Among the 15 patients who presented as cN1, 14 (93%) converted to cN0 following NAC. Of these, nine underwent SLNB and all achieved nodal pCR (100%). CONCLUSION: In this small series, 80% of OPBC patients achieved nodal pCR following NAC. pCR rates varied by receptor profile, being lowest in the ER positive/HER2 negative group and highest in the HER2 positive group (50-100%); however, these rates are excellent and numerically exceed those in the literature for IPBC. Given the pCR rate, SLNB may be an option in select OPBC patients who downstage following NAC.

Survival Outcomes for Metaplastic Breast Cancer Differ by Histologic Subtype.

BACKGROUND: Metaplastic breast carcinoma (MBC) is a rare, aggressive subtype of breast cancer associated with poorer overall survival than other triple-negative breast cancers. This study sought to compare survival outcomes among histologic subtypes of MBC with those of non-metaplastic triple-negative breast cancer. METHODS: Clinicopathologic and treatment data for all patients with non-metastatic, pure MBC undergoing surgery from 1995 to 2017 and for a large cohort of patients with other types of triple-negative breast cancer during that period were collected from an institutional database. The MBC tumors were classified as having squamous, spindle, heterologous mesenchymal, or mixed histology. Survival outcomes were compared using the Kaplan-Meier method. RESULTS: Of 132 MBC patients, those with heterologous mesenchymal MBC (n = 45) had the best 5-year overall and breast cancer-specific survival (BCSS, 88%; 95% confidence interval [CI], 0.78-0.99), whereas those with squamous MBC had the worst survival (BCSS, 56%; 95% CI, 0.32-0.79). Overall survival, BCSS, and recurrence-free survival were worse for the patients with MBC than for the patients who had non-MBC triple-negative breast cancer, with a clinicopathologically adjusted recurrence hazard ratio of 2.4 (95% CI, 1.6-3.3; p < 0.001). Of the 10 MBC patients who received neoadjuvant chemotherapy, 4 progressed while receiving treatment, and 3 had no response. CONCLUSIONS: Metaplastic breast carcinoma is associated with worse survival than other triple-negative breast cancers. The heterologous mesenchymal subtype is associated with the best survival, whereas the squamous subtype is associated with the worst survival. These data call for research to identify therapies tailored to MBC's unique biology.

The impact of MYC gene amplification on the clinicopathological features and prognosis of radiation-associated angiosarcomas of the breast.

AIMS: Radiation-associated angiosarcomas (RT-ASs) of the breast are rare tumours with a poor prognosis. MYC gene amplification is considered to be the hallmark of RT-AS, and is sometimes used as a diagnostic tool to distinguish it from other radiation-associated vascular lesions. However, a small subset of RT-ASs lacks MYC amplification, and this may be associated with better outcome. Loss of trimethylation at lysine 27 of histone 3 (H3K27me3) expression by immunohistochemistry (IHC) has been recently postulated as an additional diagnostic marker for RT-AS. The aims of this study were to evaluate the impact of MYC amplification as detected by fluorescence in-situ hybridisation and/or next-generation sequencing on clinicopathological features and outcome in a large cohort of RT-ASs, compare outcome with those of radiation-associated sarcomas (RT-Ss) of the breast other than angiosarcoma, and evaluate expression of H3K27me3 IHC in these groups. METHODS AND RESULTS: Eighty-one RT-ASs were identified, including 73 that were MYC-amplified and 8 (10%) that were MYC-non-amplified. MYC-amplified RT-ASs were diagnosed in older patients (median age, 69 years versus 61 years). The 5-year disease-specific survival and 5-year overall survival rates were 56% and 47%, respectively. Older age, larger tumour size, positive margin and MYC amplification were associated with worse prognosis. None of the RT-ASs showed complete loss of H3K27me3 IHC expression. All 18 RT-Ss were MYC-non-amplified, and complete loss of H3K27me3 expression was seen in 2 cases. We found no difference in prognosis between RT-AS and RT-S. CONCLUSIONS: RT-AS of the breast is associated with a poor prognosis. Older age at diagnosis, larger tumour size, positive margin at excision and MYC amplification are associated with worse prognosis.

Immunotherapeutic strategies in breast cancer: A clinical update.

Immunotherapy has been incorporated into the standard of care for a wide range of malignancies. The study of tumor-infiltrating lymphocytes has emphasized the importance of the host antitumor immune response in the natural history of breast cancer. Recent clinical trials have used immunotherapeutic approaches to augment this response and improve outcomes for patients with breast cancer. Here, we review several current clinical trial data that indicate checkpoint blockade may mediate clinically significant responses.

Intraoperative opioids are associated with improved recurrence-free survival in triple-negative breast cancer.

BACKGROUND: Opioid-induced immunomodulation may be of particular importance in triple-negative breast cancer (TNBC) where an immune response is associated with improved outcome and response to immunotherapy. We evaluated the association between intraoperative opioids and oncological outcomes and explored patterns of opioid receptor expression in TNBC. METHODS: Consecutive patients with stage I-III primary TNBC were identified from a prospectively maintained database. Opioid receptor expression patterns in the tumour microenvironment were analysed using publicly available bulk and single-cell RNA-seq data. RESULTS: A total of 1143 TNBC cases were retrospectively analysed. In multivariable analysis, higher intraoperative opioid dose was associated with favourable recurrence-free survival, hazard ratio 0.93 (95% confidence interval 0.88-0.99) per 10 oral morphine milligram equivalents increase (P=0.028), but was not significantly associated with overall survival, hazard ratio 0.96 (95% confidence interval 0.89-1.02) per 10 morphine milligram equivalents increase (P=0.2). Bulk RNA-seq analysis of opioid receptors showed that OPRM1 was nearly non-expressed. Compared with normal breast tissue OGFR, OPRK1, and OPRD1 were upregulated, while TLR4 was downregulated. At a single-cell level, OPRM1 and OPRD1 were not detectable; OPRK1 was expressed mainly on tumour cells, whereas OGFR and TLR4 were more highly expressed on immune cells. CONCLUSIONS: We found a protective effect of intraoperative opioids on recurrence-free survival in TNBC. Opioid receptor expression was consistent with a net protective effect of opioid agonism, with protumour receptors either not expressed or downregulated, and antitumour receptors upregulated. In this era of personalised medicine, efforts to differentiate the effects of opioids across breast cancer subtypes (and ultimately individual patients) should continue.

Changing the Default: A Prospective Study of Reducing Discharge Opioid Prescription after Lumpectomy and Sentinel Node Biopsy.

BACKGROUND: Whether routinely prescribed opioids are necessary for pain control after discharge among lumpectomy/sentinel node biopsy (Lump/SLNB) patients is unclear. We hypothesize that Lump/SLNB patients could be discharged without opioids, with a failure rate < 10%. This study prospectively examines outcomes after changing standard discharge prescription from an opioid/non-steroidal anti-inflammatory drug (NSAID) to NSAID/acetaminophen. PATIENTS AND METHODS: Standard discharge pain medication orders included opioids in the first 3-month study period and were changed to NSAID/acetaminophen in the second 3-month period. Patient-reported medication consumption and pain scores were collected by post-discharge survey. Frequency of discharge with opioid, NSAID/acetaminophen failure rate, opioid use, and pain scores were examined. RESULTS: From May to October 2019, 663 patients had Lump/SLNB: 371 in the opioid study period and 292 in the NSAID period. In the opioid period, 92% (342/371) of patients were prescribed an opioid at discharge; of 142 patients who documented opioid use on the survey, 86 (61%) used zero tablets. Among 56 (39%) patients who used opioids, the median number taken by POD 5 was 4. After the change to NSAID/acetaminophen, rates of opioid prescription decreased to 14% (41/292). The NSAID/acetaminophen failure rate was 2% (5/251). Among survey respondents, there was no significant difference in the maximum reported pain scores (POD 1-5) between the opioid period and the NSAID period (p = 0.7). CONCLUSIONS: In Lump/SLNB patients, a change to default discharge with NSAID/acetaminophen resulted in a 78% absolute reduction in opioid prescription, with a failure rate of 2% and no difference in patient-reported pain scores. Most Lump/SLNB patients can be discharged with NSAID/acetaminophen.

Microscopic Extracapsular Extension in Sentinel Lymph Nodes Does Not Mandate Axillary Dissection in Z0011-Eligible Patients.

BACKGROUND: In the ACOSOG (American College of Surgeons Oncology Group) Z0011 trial and the AMAROS (After Mapping of the Axilla: Radiotherapy or Surgery?) trial, matted nodes with gross extracapsular extension (ECE), a risk factor for locoregional recurrence, were an indication for axillary lymph node dissection (ALND), but the effect of microscopic ECE (mECE) in the sentinel lymph nodes (SLNs) on recurrence was not examined. METHODS: Between 2010 and 2017, 811 patients with cT1-2N0 breast cancer and SLN metastasis were prospectively managed according to Z0011 criteria, with ALND for those with more than two positive SLNs or gross ECE. Management of mECE was not specified. In this study, we compare outcomes of patients with one to two positive SLNs with and without mECE, treated with SLN biopsy alone (n = 685). RESULTS: Median patient age was 58 years, and median tumor size was 1.7 cm. mECE was identified in 210 (31%) patients. Patients with mECE were older, had larger tumors, and were more likely to be hormone receptor positive and HER2 negative, have two positive SLNs, and receive nodal radiation. At a median follow-up of 41 months, no isolated axillary failures were observed. There were 11 nodal recurrences; two supraclavicular ± axillary, four synchronous with breast, and five with distant failure. The five-year rate of any nodal recurrence was 1.6% and did not differ by mECE (2.3% vs. 1.3%; p = 0.84). No differences were observed in local (p = 0.08) or distant (p = 0.31) recurrence rates by mECE status. CONCLUSIONS: In Z0011-eligible patients, nodal recurrence rates in patients with mECE are low after treatment with SLN biopsy alone, even in the absence of routine nodal radiation. The presence of mECE should not be considered a routine indication for ALND.

Axillary Dissection and Nodal Irradiation Can Be Avoided for Most Node-positive Z0011-eligible Breast Cancers: A Prospective Validation Study of 793 Patients.

OBJECTIVE: To determine rates of axillary dissection (ALND) and nodal recurrence in patients eligible for ACOSOG Z0011. BACKGROUND: Z0011 demonstrated that patients with cT1-2N0 breast cancers and 1 to 2 involved sentinel lymph nodes (SLNs) having breast-conserving therapy had no difference in locoregional recurrence or survival after SLN biopsy alone or ALND. The generalizability of the results and importance of nodal radiotherapy (RT) is unclear. METHODS: Patients eligible for Z0011 had SLN biopsy alone. Prospectively defined indications for ALND were metastases in ≥3 SLNs or gross extracapsular extension. Axillary imaging was not routine. SLN and ALND groups and radiation fields were compared with chi-square and t tests. Cumulative incidence of recurrences was estimated with competing risk analysis. RESULTS: From August 2010 to December 2016, 793 patients met Z0011 eligibility criteria and had SLN metastases. Among them, 130 (16%) had ALND; ALND did not vary based on age, estrogen receptor, progesterone receptor, or HER2 status. Five-year event-free survival after SLN alone was 93% with no isolated axillary recurrences. Cumulative 5-year rates of breast + nodal and nodal + distant recurrence were each 0.7%. In 484 SLN-only patients with known RT fields (103 prone, 280 supine tangent, 101 breast + nodes) and follow-up ≥12 months, the 5-year cumulative nodal recurrence rate was 1% and did not differ significantly by RT fields. CONCLUSIONS: We confirm that even without preoperative axillary imaging or routine use of nodal RT, ALND can be avoided in a large majority of Z0011-eligible patients with excellent regional control. This approach has the potential to spare substantial numbers of women the morbidity of ALND.

Tumor Biology Predicts Pathologic Complete Response to Neoadjuvant Chemotherapy in Patients Presenting with Locally Advanced Breast Cancer.

BACKGROUND: Neoadjuvant chemotherapy (NAC) is used to convert patients with inoperable locally advanced breast cancer (LABC) to operability, but has not traditionally been used to avoid mastectomy or axillary dissection in this subset. OBJECTIVE: The purpose of this study was to determine the rates of pathologic complete response (pCR) in LABC patients, and identify factors predictive of pCR to determine if responding patients might be suitable for limited surgery. METHODS: From 2006 to 2016, 1522 patients received NAC followed by surgery; 321 had advanced disease in the breast (cT4) and/or in the nodes (cN2/N3). pCR rates were assessed by T and N stage, and receptor subtype. RESULTS: Of 321 LABC patients, 223 were cT4, 77 were cN2, and 82 were cN3. Forty-three percent were hormone receptor (HR) positive/human epidermal growth factor receptor 2 (HER2) negative (HR+/HER2-), 23% were triple negative, and 34% were HER2+. The overall pCR rate was 25% and differed by receptor subtype (HR+/HER2- 7%, triple negative 23%, HER2+ 48%; p < 0.001). Breast pCR occurred in 27% of patients and was similar in T4 versus non-T4 disease (29% vs. 22%; p = 0.26). Nodal pCR was achieved in 38% of cN+ patients and did not differ by nodal stage (cN1 43%, cN2 36%, cN3 32%; p = 0.23). Nodal pCR was significantly more common than breast pCR (p = 0.014) across all tumor subtypes. Receptor subtype was the only predictor of overall pCR (p < 0.001). CONCLUSION: In patients with LABC, pCR after NAC was seen in 25%, and did not differ by T or N stage. Tumor biology, but not extent of disease, predicted pCR. Studies assessing the feasibility of surgical downstaging with NAC in LABC patients are warranted.

How Often Does Neoadjuvant Chemotherapy Avoid Axillary Dissection in Patients With Histologically Confirmed Nodal Metastases? Results of a Prospective Study.

BACKGROUND: In breast cancer patients with nodal metastases at presentation, false-negative rates lower than 10 % have been demonstrated for sentinel node biopsy (SLNB) after neoadjuvant chemotherapy (NAC) when three or more negative sentinel nodes (SLNs) are retrieved. However, the frequency with which axillary dissection (ALND) can be avoided is uncertain. METHODS: Among 534 prospectively identified consecutive patients with clinical stages 2 and 3 cancer receiving NAC from November 2013 to November 2015, all biopsy-proven node-positive (N+) cases were identified. Patients clinically node-negative after NAC were eligible for SLNB. The indications for ALND were failed mapping, fewer than three SLNs retrieved, and positive SLNs. RESULTS: Of 288 N+ patients, 195 completed surgery, with 132 (68 %) of these patients eligible for SLNB. The median age was 50 years. Of these patients, 73 (55 %) were estrogen receptor-positive (ER+), 21 (16 %) were ER- and human epidermal growth factor receptor-2-positive (HER2+), and 38 (29 %) were triple-negative. In four cases, SLNB was deferred intraoperatively. Among 128 SLNB attempts, three or more SLNs were retrieved in 110 cases (86 %), one or two SLNs were retrieved in 15 cases (12 %), and failed mapping occurred in three cases (2 %). In 66 cases, ALND was indicated: 54 (82 %) for positive SLNs, 9 (14 %) for fewer than three negative SLNs, and 3 (4 %) for failed mapping. Persistent disease was found in 17 % of the patients with fewer than three negative SLNs retrieved. Of the 128 SLNB cases, 62 (48 %) had SLNB alone with three or more SLNs retrieved. Among 195 N+ patients who completed surgery, nodal pathologic complete response (pCR) was achieved for 49 %, with rates ranging from 21 % for ER+/HER2- to 97 % for ER-/HER2+ cases, and was significantly more common than breast pCR in ER+/HER2- and triple-negative cases. CONCLUSIONS: Nearly 70 % of the N+ patients were eligible for SLNB after NAC. For 48 %, ALND was avoided, supporting the role of NAC in reducing the need for ALND among patients presenting with nodal metastases.