Ahmed, Kamran A.

504 Background: Axillary surgery in breast cancer is used for staging and therapeutic purposes, but axillary lymph node dissection (ALND) confers high risk of complications including lymphedema. Accordingly, trials have focused on right-sizing axillary surgery, with options ranging from complete omission of surgery, sentinel lymph node (SLN) surgery, targeted axillary dissection (TAD), or ALND. Identifying a biomarker to reliably predict nodal burden would facilitate accurate selection of surgical management. We evaluated whether the presence or absence of ctDNA in the blood pre and post NAC is associated with residual nodal burden. Methods: I-SPY2 is a prospective, multicenter NAC trial for patients with clinical stage II-III high-risk breast cancer. Patients are randomized to novel NAC agents, with pathologic complete response being the primary endpoint. As part of the trial, serial ctDNA is assessed with a highly sensitive tumor-informed assay using up to 16 patient-specific tumor mutations (Signatera) at baseline, 3 weeks, 12 weeks, and post-NAC. We determined whether ctDNA positivity or negativity post-NAC, and the change in ctDNA status baseline/post-NAC (-/-, -/+, +/+, +/-) are associated with ypN category (N0, N1, N2). Results: ctDNA status was available post-NAC in 495 patients and change in ctDNA status from baseline was available in 493. At baseline, ctDNA was detected in 160/220 (72.3%) cN0 patients and 227/273 (83.2%) cN+ patients (p=0.006). Post-NAC, ctDNA was detected in 11/220 (5%) cN0 patients and 34/273 (12.5%) cN+ patients (p=0.004). While baseline ctDNA status was not associated with ypN category, there was a significant association between post-NAC ctDNA status and ypN category. For ctDNA + patients post-NAC, 33.3% were ypN0, 31.1% were ypN1, and 35.6% were ypN2 at surgery; in contrast, for ctDNA - patients post-NAC, 67.1% were ypN0, 23.1% were ypN1, and 9.8% were ypN2 (p<0.0001). Dynamic ctDNA changes were also associated with ypN category, with significantly more ypN0 patients among ctDNA -/- or ctDNA +/- cases, and more ypN2 patients in those who did not clear ctDNA (+/+) (p=0.0001, Table). Conclusions: To our knowledge this is the first study to demonstrate a significant relationship between ctDNA and ypN category, which has important surgical implications. CtDNA negativity was associated with low likelihood of ypN2 disease, making these patients excellent candidates for SLN surgery or TAD. Ongoing analyses will incorporate receptor subtype and timing of clearance of ctDNA. CtDNA in breast cancer may help tailor surgical management of the axilla, potentially reducing patient morbidity without compromising prognostic information. ctDNA baseline/post-NAC ypN0 (n=317) ypN1 (n=116) ypN2 (n=60) ctDNA -/- (n=105) 72.4% 19.1% 8.6% ctDNA -/+ (n=1) 0.0% 100.0% 0.0% ctDNA +/+ (n=44) 34.1% 29.6% 36.4% ctDNA +/- (n=343) 65.9% 23.9% 10.2%

Background We hypothesized treatment with nivolumab and stereotactic radiosurgery (SRS) would be feasible, well tolerated, and may improve intracranial tumor control over SRS alone for breast cancer brain metastases (BCBM). Methods The study is a phase Ib trial of nivolumab and SRS for BCBM. Clinical trial information: NCT03807765 . Key eligibility criteria include BCBM of all subtypes, age ≥18, Eastern Cooperative Oncology Group Performace Status (ECOG-PS)≤2 with ≤10 brain metastases. Treatment was initiated with a dose of nivolumab (480 mg intravenously) that was repeated every 4 weeks. The initial dose of nivolumab was followed 1 week later by SRS. Blood was collected at baseline and every 4 weeks for flow cytometry and cell-free DNA (cfDNA) assessment. Results A total of 12 patients received SRS to 17 brain metastases. Breast cancer subtypes included triple negative (50%), hormone receptor (HR)+/HER2− (33%), and HR−/HER2+ (17%). Median follow-up from start of protocol therapy is 56 months. No cases of radionecrosis were noted. Two lesions were noted to undergo local failure, both pathologically confirmed, for a 12-month local control of 94%. Median distant intracranial control was 7.4 months with a 12-month control rate of 33%. Median systemic progression-free survival was 7.7 months with a 12-month rate of 42%. Median overall survival (OS) was 24.7 months with a 12-month OS of 75%. Most patients were noted to have an increase in cfDNA throughout study treatment, at week 5 compared with baseline (83%), week 25 compared with baseline (89%), and 100% at first follow-up. Intracranial control was associated with lower levels of CD4 regulatory T cells (Treg) (p=0.03) and higher levels of CD4 T effector memory (p=0.04). Conclusions Nivolumab and SRS is a safe and feasible treatment option in BCBM. Long-term follow-up revealed no cases of radiation necrosis. Trial registration number NCT03807765 .

2027 Background: Breast cancer related leptomeningeal disease (BC-LMD) is a dire diagnosis for 5-8% of breast cancer patients with overall survival (OS) measured in weeks without treatment. As new treatments prolong survival with breast cancer, the risk of developing BC-LMD may be increasing. We hypothesized that the rate of BC-LMD diagnosis increased significantly with time. We also predicted that OS with BC-LMD had changed with time and in relationship to molecular subtype and treatment following BC-LMD diagnosis. Methods: With approval of the local Scientific Research Committee and IRB, we conducted a retrospective analysis of medical records for patients treated or diagnosed with breast cancer at MCC from 2011-2020. Patient demographics, tumor characteristics, treatments, and outcomes were collected. Kaplan Meier survival curves were used to determine median overall survival (OS), progression of disease, and differences by molecular subtype. Univariate and multivariate analyses were used to determine characteristics of primary tumors and treatments which affected OS. Results: Of the 133 cases identified, significantly more were diagnosed between 2016-2020 than 2011-2015 (p < 0.01). Significant increases were seen in HER2+ and TNBC patients (p < 0.05) but not for ER/PR positive (HR+) disease (p = 0.058). HER2+ LMD associated with longest overall survival (OS; 7mths) followed by HR+ disease (3mths) and TNBC with the shortest OS (2mths). Systemic metastases preceded BC-LMD diagnosis in 72% of cases and CNS metastases in 85% of cases. HER2+ disease also conferred increased survival after CNS metastases were diagnosed until progression to LMD (8mth vs 2mth for HR+ and 1mth for TNBC LMD; p < 0.05). Positive impact on survival by HER2 targeted therapies may account for improved OS in this population. Other factors which increased OS generally were: WBRT, continuation of systemic therapy, delivery of intrathecal chemotherapy, and participation in clinical trials. Having TNBC and decision to defer treatment were associated with reduced OS. Conclusions: This study highlights the importance of identifying patients with BC-LMD early and with the intention to treat. Prospective clinical trials and population-based studies are needed to advance treatment of BC-LMD.

Introduction: Nummular headache is a rare primary headache disorder described by a focal circumscribed area of pain (2–6 cm in diameter). Literature on this disorder is sparse. Patients and methods: Here, we describe a case series of 16 patients (6 men, 10 women) seen at the Mayo Clinic. Results: Mean age of onset was 50 years (range, 19–79 years) and mean duration of headache was 7.9 years (range, 0.33–40 years). Location of headache varied and was found to be an average of 3.9 cm in diameter (range, 2–10 cm). Headache was episodic (<15 days/month) in four patients and chronic (>15 days/month) in 12 patients. Attention was paid to therapeutic interventions. Resolution was seen in 38% of patients. Migraine was present in the history of 56% of patients and medication overuse headache was found in 25%. Conclusions: Our series results support previous findings. In our population, no specific therapy was identified to be effective in more than one patient.