Intratumor mapping of intracellular water lifetime: metabolic images of breast cancer?

Shutter-speed pharmacokinetic analysis of dynamic-contrast-enhanced (DCE)-MRI data allows evaluation of equilibrium inter-compartmental water interchange kinetics. The process measured here - transcytolemmal water exchange - is characterized by the mean intracellular water molecule lifetime (τi). The τi biomarker is a true intensive property not accessible by any formulation of the tracer pharmacokinetic paradigm, which inherently assumes it is effectively zero when applied to DCE-MRI. We present population-averaged in vivo human breast whole tumor τi changes induced by therapy, along with those of other pharmacokinetic parameters. In responding patients, the DCE parameters change significantly after only one neoadjuvant chemotherapy cycle: while K(trans) (measuring mostly contrast agent (CA) extravasation) and kep (CA intravasation rate constant) decrease, τi increases. However, high-resolution, (1 mm)(2), parametric maps exhibit significant intratumor heterogeneity, which is lost by averaging. A typical 400 ms τi value means a trans-membrane water cycling flux of 10(13) H2O molecules s(-1)/cell for a 12 µm diameter cell. Analyses of intratumor variations (and therapy-induced changes) of τi in combination with concomitant changes of ve (extracellular volume fraction) indicate that the former are dominated by alterations of the equilibrium cell membrane water permeability coefficient, PW, not of cell size. These can be interpreted in light of literature results showing that τi changes are dominated by a PW (active) component that reciprocally reflects the membrane driving P-type ATPase ion pump turnover. For mammalian cells, this is the Na(+), K(+)-ATPase pump. These results promise the potential to discriminate metabolic and microenvironmental states of regions within tumors in vivo, and their changes with therapy.

Estrogen receptor, progesterone receptor, interleukin-6 and interleukin-8 are variable in breast cancer and benign stem/progenitor cell populations.

BACKGROUND: Estrogen receptor positive breast cancers have high recurrence rates despite tamoxifen therapy. Breast cancer stem/progenitor cells (BCSCs) initiate tumors, but expression of estrogen (ER) or progesterone receptors (PR) and response to tamoxifen is unknown. Interleukin-6 (IL-6) and interleukin-8 (IL-8) may influence tumor response to therapy but expression in BCSCs is also unknown. METHODS: BCSCs were isolated from breast cancer and benign surgical specimens based on CD49f/CD24 markers. CD44 was measured. Gene and protein expression of ER alpha, ER beta, PR, IL-6 and IL-8 were measured by proximity ligation assay and qRT-PCR. RESULTS: Gene expression was highly variable between patients. On average, BCSCs expressed 10-106 fold less ERα mRNA and 10-103 fold more ERß than tumors or benign stem/progenitor cells (SC). BCSC lin-CD49f-CD24-cells were the exception and expressed higher ERα mRNA. PR mRNA in BCSCs averaged 10-104 fold less than in tumors or benign tissue, but was similar to benign SCs. ERα and PR protein detection in BCSCs was lower than ER positive and similar to ER negative tumors. IL-8 mRNA was 10-104 higher than tumor and 102 fold higher than benign tissue. IL-6 mRNA levels were equivalent to benign and only higher than tumor in lin-CD49f-CD24-cells. IL-6 and IL-8 proteins showed overlapping levels of expressions among various tissues and cell populations. CONCLUSIONS: BCSCs and SCs demonstrate patient-specific variability of gene/protein expression. BCSC gene/protein expression may vary from that of other tumor cells, suggesting a mechanism by which hormone refractory disease may occur.

Association of Residual Ductal Carcinoma In Situ With Breast Cancer Recurrence in the Neoadjuvant I-SPY2 Trial.

Importance: Pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC) in breast cancer strongly correlates with overall survival and has become the standard end point in neoadjuvant trials. However, there is controversy regarding whether the definition of pCR should exclude or permit the presence of residual ductal carcinoma in situ (DCIS). Objective: To examine the association of residual DCIS in surgical specimens after neoadjuvant chemotherapy for breast cancer with survival end points to inform standards for the assessment of pathologic complete response. Design, Setting, and Participants: The study team analyzed the association of residual DCIS after NAC with 3-year event-free survival (EFS), distant recurrence-free survival (DRFS), and local-regional recurrence (LRR) in the I-SPY2 trial, an adaptive neoadjuvant platform trial for patients with breast cancer at high risk of recurrence. This is a retrospective analysis of clinical specimens and data from the ongoing I-SPY2 adaptive platform trial of novel therapeutics on a background of standard of care for early breast cancer. I-SPY2 participants are adult women diagnosed with stage II/III breast cancer at high risk of recurrence. Interventions: Participants were randomized to receive taxane and anthracycline-based neoadjuvant therapy with or without 1 of 10 investigational agents, followed by definitive surgery. Main Outcomes and Measures: The presence of DCIS and EFS, DRFS, and LRR. Results: The study team identified 933 I-SPY2 participants (aged 24 to 77 years) with complete pathology and follow-up data. Median follow-up time was 3.9 years; 337 participants (36%) had no residual invasive disease (residual cancer burden 0, or pCR). Of the 337 participants with pCR, 70 (21%) had residual DCIS, which varied significantly by tumor-receptor subtype; residual DCIS was present in 8.5% of triple negative tumors, 15.6% of hormone-receptor positive tumors, and 36.6% of ERBB2-positive tumors. Among those participants with pCR, there was no significant difference in EFS, DRFS, or LRR based on presence or absence of residual DCIS. Conclusions and Relevance: The analysis supports the definition of pCR as the absence of invasive disease after NAC regardless of the presence or absence of DCIS. Trial Registration: ClinicalTrials.gov Identifier NCT01042379.

A prospective study of opioid use for postoperative pain management after breast operation.

BACKGROUND: The opioid epidemic has necessitated increased attention to prescribing practices. This study seeks to prospectively quantify postoperative opioid use after breast operation. METHODS: Consecutive patients undergoing breast operation at a single institution in 2018 prospectively tracked each dose of medication and completed a survey of perceptions regarding their opioid prescription. RESULTS: Of 100 patients, 88 completed log, survey, or both. The tab quantity required to fulfill the needs of 80% of patients was: Partial mastectomy (PM) 3, PM with sentinel lymph node biopsy 6, PM with bilateral reduction 8, total mastectomy 34, and bilateral mastectomy 47. Of survey respondents, 51.2% felt they had been prescribed too much pain medication. Most (83.0%) had leftover tabs, and 67.9% indicated they kept them in their home. CONCLUSIONS: The majority of patients were overprescribed opioids after breast operation. A reduction could be achieved by targeting the needs of 80% of the population.

Surgical resection of breast cancers: Molecular analysis of cancer stem cells in residual disease.

BACKGROUND: Approximately 70% of breast cancer patients have residual disease after neoadjuvant chemotherapy. This study was designed to determine whether breast cancer cells with stemlike properties are present in residual disease after neoadjuvant chemotherapy and whether they exhibit oncogenic mutations. The presence of breast cancer cells with stemlike properties with specific mutations may help explain the poor prognosis associated with residual disease. METHODS: A total of 68 breast cancer specimens were collected at the time of mastectomy or lumpectomy. A total of 44 were chemotherapy naïve and 24 were collected as residual disease after neoadjuvant chemotherapy. Tumor cells were collected by fluorescence-activated cell sorting, with breast cancer cells with stemlike properties specifically identified using breast stem cell associated antibodies. Whole tumor specimens and fluorescence-activated cell sorting breast cancer cells with stemlike properties were analyzed for genetic mutations, including PIK3CA. RESULTS: Breast cancer cells with stemlike properties, demonstrating EpCAM-positive, CD44-positive, CD49f±, CD24± expression were present in chemotherapy-naïve tumors and residual disease. In both chemotherapy-naïve and residual disease specimens the highest frequency of PIK3CA mutations were detected in CD49f-CD24+ BCSCs (39% and 33%, respectively). PIK3CA mutations were detected in all stages of breast cancer (35%), in both chemotherapy naïve (39%) and residual disease (29%) and in both estrogen receptor positive (41%) and negative tumors (14%) (P = ns). Various PIK3CA mutations were identified in chemotherapy-naïve specimens versus residual disease specimens in both patient-paired and unpaired breast cancers. CONCLUSION: Breast cancer cells with stemlike properties with mutations in PIK3CA were present in chemotherapy-naïve breast cancers and residual disease after neoadjuvant chemotherapy. These results demonstrate that neoadjuvant chemotherapy does not completely eradicate PIK3CA-defective breast cancer cells with stemlike properties. Although these findings may help explain the poor clinical outcomes in patients with residual disease, they also identify breast cancer cells with stemlike-property targets for therapies.

Intravenous and isolated limb perfusion delivery of wild type and a tumor-selective replicating mutant vaccinia virus in nonhuman primates.

In this study we examine the safety, feasibility, and biodistribution of a tumor-selective mutant vaccinia (vvDD) and wild-type WR (vF13) vaccinia after delivery via intradermal or intravenous infection or isolated limb perfusion (ILP) in rhesus macaques. By intradermal inoculation, 10(6) PFU of vvDD caused a minimal skin reaction whereas vF13 caused marked erythema and necrosis with a peak indurated area of 108 cm2. By intravenous delivery, vvDD caused no clinical symptoms of viremia and no viral recovery from tissues, serum, saliva, urine, or feces. In contrast, vF13 caused symptoms of lethargy, anorexia, fever, and signs of viremia. Delivery of vF13 via ILP resulted in numerous cutaneous pox lesions localized solely to the perfused limb with high viral recovery in the perfused skin and muscle. ILP with vvDD resulted in no visible pox lesions and no clinical signs or symptoms of viremia. No long-term toxicity was identified after ILP with 10(9) PFU of vvDD, and no virus was recovered from any tissue, serum, saliva, urine, or fecal sample. These results suggest that vvDD appears to be safe in primates, and thus vvDD should be further investigated for clinical trial in human cancer patients.

Manufacture and evaluation of 3-dimensional printed sizing tools for use during intraoperative breast brachytherapy.

Three-dimensional (3D) printing has emerged as a promising modality for the production of medical devices. Here we describe the design, production, and implementation of a series of sizing tools for use in an intraoperative breast brachytherapy program. These devices were produced using a commercially available low-cost 3D printer and software, and their implementation resulted in an immediate decrease in consumable costs without affecting the quality of care or the speed of delivery. This work illustrates the potential of 3D printing to revolutionize the field of medical devices, enabling physicians to rapidly develop and prototype novel tools.

Cystic Neutrophilic Granulomatous Mastitis: Association With Gram-Positive Bacilli and Corynebacterium.

OBJECTIVES: To determine whether cystic neutrophilic granulomatous mastitis (CNGM) can be associated with Gram-positive bacilli and Corynebacterium METHODS: We reviewed our experience with 35 granulomatous mastitis patients over a 10-year period, including histologic pattern, Gram stain and other microbiologic data, clinical presentation, treatment and outcome. RESULTS: Biopsies from 19 patients demonstrated CNGM, while 16 patients had other patterns of granulomatous mastitis. Gram-positive organisms were seen within microcystic spaces in 16/19 CNGM, but 0/16 non-CNGM patients (P = .000). Culture or molecular studies demonstrated Corynebacterium species in three, all CNGM. Patients with CNGM were more likely to be younger, of Hispanic ethnicity, and born outside of the United States. Granulomatous mastitis resolved after a protracted course with widely variable treatment (antibiotics, surgery, steroids). CONCLUSIONS: Our data further support CNGM as an infectious disease; further study of Corynebacterium-directed therapy in CNGM is needed.

Sulforaphane Bioavailability and Chemopreventive Activity in Women Scheduled for Breast Biopsy.

Epidemiologic studies suggest a protective effect of cruciferous vegetables on breast cancer. Sulforaphane (SFN), an active food component derived from crucifers, has been shown to be effective in breast cancer chemoprevention. This study evaluated the chemopreventive effect of SFN on selective biomarkers from blood and breast tissues. In a 2- to 8-week double-blinded, randomized controlled trial, 54 women with abnormal mammograms and scheduled for breast biopsy were randomized to consume a placebo or a glucoraphanin (GFN) supplement providing SFN (n = 27). Plasma and urinary SFN metabolites, peripheral blood mononuclear cell (PBMC) histone deacetylase (HDAC) activity, and tissue biomarkers (H3K18ac, H3K9ac, HDAC3, HDAC6, Ki-67, p21) were measured before and after the intervention in benign, ductal carcinoma in situ, or invasive ductal carcinoma breast tissues. Within the supplement group, Ki-67 (P = 0.003) and HDAC3 (P = 0.044) levels significantly decreased in benign tissue. Pre-to-postintervention changes in these biomarkers were not significantly different between treatment groups after multiple comparison adjustment. GFN supplementation was associated with a significant decrease in PBMC HDAC activity (P = 0.04). No significant associations were observed between SFN and examined tissue biomarkers when comparing treatment groups. This study provides evidence that GFN supplementation for a few weeks is safe but may not be sufficient for producing changes in breast tissue tumor biomarkers. Future studies employing larger sample sizes should evaluate alternative dosing and duration regimens to inform dietary SFN strategies in breast cancer chemoprevention.

Indigent breast cancer patients among all racial and ethnic groups present with more advanced disease compared with nationally reported data.

BACKGROUND: This study examines the epidemiologic and pathologic characteristics of indigent breast cancer patients followed up in a public city hospital in comparison to national standards. METHODS: A prospective oncology database was queried to identify all patients presenting with primary breast cancer. Medical records of 188 patients identified between March 1997 and May 2002 were retrospectively reviewed. Pathologic and epidemiologic data were compared with 1998 data reported by the Surveillance, Epidemiology, and End Results (SEER) program. RESULTS: Among the patient population 10% were Caucasian, 13% African-American, 49% Hispanic, 25% Chinese, and 6% were of other background. The majority of patients were uninsured. Indigent patients within each ethnic group presented with more advanced disease when compared with patients reported by SEER. CONCLUSIONS: Indigent patients among all ethnic and racial backgrounds present with more advanced disease when compared with national statistics reported by SEER. The majority of these patients is uninsured and would benefit from more aggressive education, screening, detection methods, and follow-up.

Correlation of breast cancer axillary lymph node metastases with stem cell mutations.

IMPORTANCE: Mutations in oncogenes AKT1, HRAS, and PIK3CA in breast cancers result in abnormal PI3K/Akt signaling and tumor proliferation. They occur in ductal carcinoma in situ, in breast cancers, and in breast cancer stem and progenitor cells (BCSCs). OBJECTIVES: To determine if variability in clinical presentation at diagnosis correlates with PI3K/Akt mutations in BCSCs and provides an early prognostic indicator of increased progression and metastatic potential. DESIGN, SETTING, AND PARTICIPANTS: Malignant (BCSCs) and benign stem cells were collected from fresh surgical specimens via cell sorting and tested for oncogene mutations in a university hospital surgical oncology research laboratory from 30 invasive ductal breast cancers (stages IA through IIIB). MAIN OUTCOMES AND MEASURES: Presence of AKT1, HRAS, and PIK3CA mutations in BCSCs and their correlation with tumor mutations, pathologic tumor stage, tumor histologic grade, tumor hormone receptor status, lymph node metastases, and patient age and condition at the last follow-up contact. RESULTS: Ten tumors had mutations in their BCSCs. In total, 9 tumors with BCSC mutations and 4 tumors with BCSCs without mutations had associated tumor present in the lymph nodes (P = .001). CONCLUSIONS AND RELEVANCE: Tumors in which BCSCs have defects in PI3K/Akt signaling are significantly more likely to manifest nodal metastases. These oncogenic defects may be missed by gross molecular testing of the tumor and are markers of more aggressive breast cancer. Molecular profiling of BCSCs may identify patients who would likely benefit from PI3K/Akt inhibitors, which are being tested in clinical trials.

Impact of American College of Surgeons Oncology Group Z0011 and National Surgical Adjuvant Breast and Bowel Project B-32 trial results on surgeon practice in the Pacific Northwest.

BACKGROUND: Recent clinical trials have suggested no survival benefit for completion axillary node dissection (CALND) after sentinel lymph node biopsy (American College of Surgeons Oncology Group Z0011) and no clinically meaningful benefit for the routine use of immunohistochemistry (National Surgical Adjuvant Breast and Bowel Project B-32) in clinically node-negative breast cancer. METHODS: A 12-question electronic survey was distributed to members of 3 Pacific Northwest surgical societies. Surgeons were queried regarding the impact of the trial results on their surgical management of breast cancer. RESULTS: The 181 respondents reported performing fewer CALNDs (63%), fewer intraoperative frozen sections (21%), and no immunohistochemistry (12%) because of trial data. However, 28% of surgeons continued to perform CALND in patients with 1 to 2 positive sentinel lymph nodes undergoing lumpectomy and postoperative radiation. CONCLUSIONS: Recent trial data have impacted the performance of CALNDs and the pathological evaluation of sentinel lymph nodes among Pacific Northwest surgeons. Our results suggest a need for regional surgical societies to disseminate practice-changing trial data to members.

Comparative validation of online nomograms for predicting nonsentinel lymph node status in sentinel lymph node-positive breast cancer.

BACKGROUND: Completion axillary lymph node dissection is recommended for patients with metastases to the sentinel lymph node (SLN) in breast cancer although nonsentinel lymph nodes (NSLN) are often negative for tumor. Online nomograms are available to predict risk of NSLN disease. OBJECTIVE: To compare the accuracy of the Memorial Sloan-Kettering Cancer Center (MSKCC) nomogram (using 9 variables) with the Stanford nomogram (using 3 variables) in predicting NSLN metastasis. SETTING: A single academic center. PATIENTS: Prospectively maintained database of patients with breast cancer who underwent SLN biopsy from October 1, 1999, through January 31, 2008. METHODS: Risk of NSLN metastasis was calculated using each nomogram's online calculator. Results from the axillary lymph node dissection were reviewed for positive NSLNs. Nomograms were evaluated using the area under the receiver operating characteristic curve, false-negative rates, positive predictive value, and calibration plot. MAIN OUTCOME MEASURES: Nomogram scores and axillary lymph node dissection results. RESULTS: Of 579 patients who underwent SLN biopsy, 179 (30.9%) had a positive SLN. For 123 patients who underwent axillary lymph node dissection, the area under the curve for the MSKCC and Stanford nomograms was 0.72 and 0.70, respectively. False-negative rates for nomogram values of 10% or less were low (4.1% for the MSKCC and 7.8% for the Stanford). The positive predictive value for nomogram probabilities of 80% or greater was higher for MSKCC than for Stanford (90.9% vs 61.8%). The Stanford nomogram performed more accurately in low-risk patients with isolated tumor cells or micrometastatic SLN disease; however, the MSKCC nomogram more accurately predicted NSLN outcomes across the entire study population. CONCLUSION: Although the MSKCC and Stanford nomograms performed similarly on the basis of the area under the curve, the MSKCC nomogram was consistently more reliable in predicting actual NSLN outcomes.

Factors influencing accuracy of axillary sentinel lymph node frozen section for breast cancer.

BACKGROUND: Intraoperative sentinel lymph node (SLN) frozen section (FS) guides immediate axillary lymph node dissection in breast cancer patients. METHODS: The Oregon Health & Science University pathology database was searched for SLN FS From October 1999 to January 1, 2009. Slides of positive cases were reviewed and metastasis sizes measured. RESULTS: Of 416 cases, 129 were positive (31%) on permanent sections and immunohistochemistry, with 79 concordant and 50 false-negative FS. Accuracy was 88%, sensitivity 61%, and specificity 100%. FS accuracy for lobular carcinoma (76%) was lower than for invasive ductal carcinoma (88%) (P = .048). FS accuracy significantly differed by size of nodal tumor. For 49 cases of tumor 2-mm metastases, accuracy was 90% (P < .0001). CONCLUSIONS: False-negative FS were predominantly small nodal tumor deposits not sampled at FS. Although accuracy was lower, SLN FS is still beneficial in lobular carcinoma, but not ductal carcinoma in situ.

Using complications associated with postmastectomy radiation and immediate breast reconstruction to improve surgical decision making.

OBJECTIVES: To identify factors independently associated with surgical complications in oncologic and reconstructive surgery and to examine sentinel lymph node (SLN) biopsy data, along with variables that are typically known prior to definitive resection, for their ability to impact the prediction of need for postmastectomy irradiation (PMRT). DESIGN: Retrospective review. SETTING: University hospital. PATIENTS: Mastectomy patients with stage I to III breast cancer treated in 2000 to 2008. MAIN OUTCOME MEASURES: Complication rates of oncologic and reconstructive surgery requiring reoperation and clinicopathologic variables that independently predict complications and/or PMRT administration by multivariate analysis. RESULTS: Among 100 of 302 mastectomy patients who underwent PMRT, complications occurred in 44% who underwent immediate breast reconstruction (IBR) and 7% who did not (P < .001). Postmastectomy irradiation independently predicted the occurrence of a complication (odds ratio, 3.3; P < .001). Implants were removed in 31% of patients who underwent PMRT and 6% of patients who did not (P = .005). Three percent of patients with T2 or smaller tumors and zero positive SLN required PMRT. Among those with T2 tumors, 49% with a positive axilla lymph node underwent PMRT. Independent predictors of PMRT need were T2 vs T1 tumors, positive axillary lymph node status, and the number of positive SLNs, with odds ratios of 5.8 (P < .001), 14.5 (P < .001), and 2.1 (P = .001), respectively. CONCLUSIONS: Postmastectomy irradiation was associated with a high rate of surgical complications and implant loss among patients who underwent IBR. Determining the number of positive SLNs prior to definitive resection and reconstructive operations may reduce complications and implant loss by guiding surgical decision making. Patients with a negative SLN are unlikely to require PMRT. Those with positive SLN(s) are high-risk IBR candidates with a quantifiable PMRT risk.

A declining rate of completion axillary dissection in sentinel lymph node-positive breast cancer patients is associated with the use of a multivariate nomogram.

OBJECTIVE: To compare sentinel lymph node (SLN)-positive breast cancer patients who had completion axillary dissection (ALND) with those who did not, with particular attention to clinicopathologic features, nomogram scores, rates of axillary local recurrence (LR), and changes in treatment pattern over time. BACKGROUND: While conventional treatment of SLN-positive patients is to perform ALND, there may be a low-risk subgroup of SLN-positive patients in whom ALND is not required. A multivariate nomogram that predicts the likelihood of residual axillary disease may assist in identifying this group. METHODS: Among 1960 consecutive SLN-positive patients (1997-2004), 1673 (85%) had ALND ("SLN+/ALND") and 287 (15%) did not ("SLN+/no ALND"). We compare in detail the clinicopathologic features, nomogram scores, and rates of axillary LR between groups. RESULTS: Compared with the SLN+/ALND group, patients with SLN+/no ALND were older, had more favorable tumors, were more likely to have breast conservation, had a lower median predicted risk of residual axillary node metastases (9% vs. 37%, P < 0.001), and had a marginally higher rate of axillary LR (2% vs. 0.4%, P = 0.004) at 23 to 30 months' follow-up; half of all axillary LR in SLN+/no ALND patients were coincident with other local or distant sites. For patients in whom intraoperative frozen section was either negative or not done, the rate of completion ALND declined from 79% in 1997 to 62% in 2003 to 2004 but varied widely by surgeon, ranging from 37% to 100%. For 10 of 10 evaluable surgeons, the median nomogram scores in the SLN+/no ALND group were

The risk of axillary relapse after sentinel lymph node biopsy for breast cancer is comparable with that of axillary lymph node dissection: a follow-up study of 4008 procedures.

OBJECTIVE: We sought to identify the rate of axillary recurrence after sentinel lymph node (SLN) biopsy for breast cancer. SUMMARY BACKGROUND DATA: SLN biopsy is a new standard of care for axillary lymph node staging in breast cancer. Nevertheless, most validated series of SLN biopsy confirm that the SLN is falsely negative in 5-10% of node-positive cases, and few studies report the rate of axillary local recurrence (LR) for that subset of patients staged by SLN biopsy alone. METHODS: Through December of 2002, 4008 consecutive SLN biopsy procedures were performed at Memorial Sloan-Kettering Cancer Center for unilateral invasive breast cancer. Patients were categorized in 4 groups: SLN-negative with axillary lymph node dissection (ALND; n = 326), SLN-negative without ALND (n = 2340), SLN-positive with ALND (n = 1132), and SLN-positive without ALND (n = 210). Clinical and pathologic characteristics and follow-up data for each of the 4 cohorts were evaluated with emphasis on patterns of axillary LR. RESULTS: With a median follow-up of 31 months (range, 1-75), axillary LR occurred in 10/4008 (0.25%) patients overall. In 3 cases (0.07%) the axillary LR was the first site of treatment failure, in 4 (0.1%) it was coincident with breast LR, and in 3 (0.07%) it was coincident with distant metastases. Axillary LR was more frequent among the unconventionally treated SLN-positive/no ALND patients than in the other 3 conventionally treated cohorts (1.4% versus 0.18%, P = 0.013). CONCLUSIONS: Axillary LR after SLN biopsy, with or without ALND, is a rare event, and this low relapse rate supports wider use of SLN biopsy for breast cancer staging. There is a low-risk subset of SLN-positive patients in whom completion ALND may not be required.