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e18050 Background: Adenoid cystic carcinoma (ACC) is a rare malignancy of glandular tissue with a high rate of local recurrence and metastatic disease for which clinical behavior varies widely. Currently, no standard therapy exists, and available therapies have low response rates. Therefore, prognostic biomarkers to determine optimal treatment strategies are urgently needed. Here we investigate the molecular landscape and therapeutic targets of ACC. Methods: ACC samples were analyzed using next generation sequencing (NGS) (NextSeq, 592 gene panel) or whole exome sequencing (NovaSeq) (Caris Life Sciences, Phoenix, AZ). Pathogenic fusion events were detected using whole transcriptome sequencing (NovaSeq). Statistical significance was determined using the Chi-square test and adjusted for multiple comparisons. Tumor infiltrating Immune cell fractions were determined using the QuanTIseq deconvolution algorithm and WTS data. Results: 327 ACC patients were identified, median age of 58 years, 62% female and 62% metastatic disease. The most frequent mutations (excluding indeterminate results) involved genes in the NOTCH pathway ( NOTCH1 16% [41 of 298 cases]), chromatin remodeling ( ARID1A 24.3% [27 of 138 cases], KDM6A 12.5% [28 of 224 cases], KMT2C 10.7% [21 of 197 cases]) and TP53 10.2% (25 of 246 cases). Chromatin remodeling genes were co-mutated with NOTCH1. NOTCH1 mutations were found in 41 cases, 18 primary and 23 metastatic were associated with reduced median overall survival (mOS 1.8 years vs 3.8 years, p = 0.01). Mutations were most frequent in the PEST (n = 35), NRR (n = 18), PEST+NRR (n = 16) and EGF-like domains (n = 11). PEST domain mutations were found exclusively in ACC originating from the head and neck (H&N). GSEA showed that MYC, E2F and G2M target pathways were enriched in NOTCH1 mutated ACC regardless of the presence of MYB fusions. All three pathways were enriched in PEST domain mutations whereas only MYC targets were enriched in NRR and NRR+PEST domain mutations indicating that PEST domain mutations drive transcriptomic changes in NOTCH1 mutated ACC. MYC gene expression was significantly upregulated in NOTCH1 mutated ACC. Fusion events were detected in 45% (104/231). MYB:NFIB was the most common fusion (40%) and was more frequent in H&N origin than other sites. There was no difference in the mOS between MYB fusion positive and negative ACC (4.4 years vs 5.5 years, p = 0.14). M2-polarized macrophages, myeloid dendritic cells and neutrophils were significantly higher in metastatic compared to primary ACC while NK cells were more abundant in primary tumor. Conclusions: ACC is a genetically heterogenous disease with an immune-excluded microenvironment. NOTCH1 mutations were associated with worse, while MYB:NFIB fusion was not associated with prognosis. Our study shows that M2 macrophages and MYC are potential novel therapeutic targets in ACC.

6031 Background: Salvage surgery for locally recurrent head and neck squamous cell carcinoma (rHNSCC) results in local control rates of 33-50% but only 20-40% of patients achieve long-term survival necessitating additional therapy (Haque et al., Oral Oncol. 2019). Many patients are ineligible for re-irradiation and chemotherapy alone after salvage surgeryhas shown no survival benefit. The clinical activity and tolerability of immune checkpoint inhibitors has been demonstrated in metastatic HNSCC, but the benefit after salvage surgery (SS) has not been studied. Here we report the results of a multi-center phase II investigation of nivolumab, a PD-1 inhibitor, after SS in recurrent HNSCC (NCT03355560). Methods: HNSCC patients undergoing curative-intent SS were enrolled to receive 6 months of nivolumab beginning 4-11 weeks after surgery. All received radiation with or without chemotherapy as prior definitive therapy and had no other curative treatment options at the time of surgery. Key exclusion criteria included: distant metastatic disease, gross residual disease, or a history of immunodeficiency, autoimmunity, or pneumonitis. The primary endpoint was 2-year disease-free survival (DFS) measured by Kaplan Meier curves. Safety was evaluated by CTCAE v5.0. Results: 39 patients were enrolled. Median age was 68 years (range, 49-85). 12/39 (31%) were female. 34/39 (87%) were white. Disease sites included oropharynx 9/39 (23%), oral cavity 14/39 (36%), and larynx 16/39 (41%). P16 status was 26% (+), 48% (-), and 26% (unknown). 17/39 (44%) had high risk pathologic features (positive margins or extranodal spread) at time of SS. 28/39 (72%) patients experienced treatment-related adverse events (TRAE), the most common of which were fatigue (26%), hypothyroidism (10%) and acneiform rash (13%). Grade 3-4 TRAEs were rare, occurring in 3/39 (8%) patients and included diarrhea, oral pain, neck pain, productive cough, stridor, and COPD exacerbation. 3/39 (8%) required treatment discontinuation and there were no grade 5 events. The 2-year DFS was 60% (95%CI 0.39-0.91). 2-year overall survival was 74% (95% CI 0.54-1). In single-cell multiplex cytokine analysis, patients who relapsed following adjuvant nivolumab had a significantly higher proportion of peripheral blood CD8 T cells which displayed a polyfunctional cytokine profile. IFN-γ and Granzyme were the dominant CD8 cytokines in both responders and non-responders, however CD8 expression of MIP1a and TNF-α were significantly higher in patients who ultimately relapsed. Conclusions: Nivolumab after salvage surgery in rHNSCC is well tolerated and shows promising antitumor activity in this high-risk patient population with unmet need. Immunotherapy after salvage surgery should be studied in randomized clinical trials. Clinical trial information: NCT03355560.

e18056 Background: Adenoid cystic carcinoma (ACC) is a rare malignancy of glandular tissue with a high rate of local recurrence and metastatic disease. Despite being regarded as an indolent disease, the clinical course of recurrent and metastatic ACC (R/M ACC) is highly variable. Responses to chemotherapy (chemo) are uniformly poor. Several multi-targeted tyrosine-kinase inhibitors (mTKIs), EGFR inhibitors (EGFRi) and other targeted agents have been studied in single-arm early phase trials with response rates ranging from 0-16% and progression free survival ranging from 2.5-17 months. However, there have been no comparative clinical trials and it is not known if one treatment strategy is superior. We undertook this retrospective study to assess the real-world clinical outcomes in patients with adenoid cystic carcinoma using the Caris Life Sciences database. Methods: Real world overall survival (rwOS) for cases of ACC was obtained from insurance claims data and Kaplan-Meier estimates were calculated from the date of collection to the date of last contact. Cases were divided into subgroups based on treatment received – chemo (including platinum agents, taxanes, 5FU, topoisomerase inhibitors, anthracyclines), EGFRi (cetuximab, erlotinib, lapatinib), mTKIs (pazopanib, axitinib, sunitinib, cabozantinib, lenvatinib, sorafenib) and immune checkpoint inhibitors (ICIs) (atezolizumab, ipilimumab, pembrolizumab, nivolumab). Results: 368 patients (pts) were identified with ACC, 16 were locally recurrent and 216 tumors were taken from metastatic sites. 50 pts received chemo, 6 were treated with EGFRi and 15 with mTKIs. Pts who received combination EGFRi and chemo or mTKI and chemo were excluded. The median overall survival (mOS) all patients with metastatic ACC was 2.8 years (yrs). The mOS of pts with R/M ACC was 3 yrs for chemo, 2.9 yrs for EGFRi and 1.5 yrs for mTKIs. There was no significance in mOS between chemo vs mTKIs (HR 0.85, 95% CI 0.3 - 2, p = 0.72) and chemo vs EGFRi (HR = 0.88, 95% CI 0.3 - 2.5, p = 0.78). We further compared the outcomes of those treated with EGFRi (n = 8) with mTKIs (n = 19) in the entire cohort. For most pts, these agents were given as front line therapy. 25% (2/8) of patients had received treatment prior to EGFRi and 20% (4/9) prior to mTKIs (p = 1). There was no significant difference in mOS with HR 0.6 (95% CI 0.16 - 2.6), p = 0.6. We also compared the mOS of patients who received ICIs (n = 22) with those who did not (n = 346) but there was no significant difference (mOS 3.19 vs 3.17 yrs respectively, HR 0.87, 95% CI 0.47- 1.61, p = 0.65). Conclusions: There was no significant difference in the mOS between pts with R/M ACC who were treated with chemo, EGFRi or TKIs and in those who received ICIs compared to those who did not in our limited patient population. This highlights the need for predictive biomarkers for better patient selection with the goal of personalizing treatment strategies for this disease.

6576 Background: Immune checkpoint inhibitors (ICIs) are FDA approved for use in head and neck squamous cell cancer (HNSCC), however, only ~20% patients achieve a response. Identification of biomarkers of response or toxicity remains a challenge. Polyfunctional T-cells, or T-cells producing multiple cytokines, have been recognized as contributors to durable immunity against various cancers. However, their role has not been studied prospectively in HNSCC patients receiving ICIs. To look for an early predictor of response, we used single-cell functional proteomic profiling (IsoPlexis) on blood samples pre- and post- first dose of nivolumab (nivo) in patients on our phase-II study of locally recurrent HNSCC (NCT03355560). Methods: HNSCC patients who failed definitive radiation +/-chemotherapy and were subsequently treated with curative intent salvage resection were enrolled to receive 6 months of nivo beginning 4 to 11 weeks after surgery. Blood samples were collected before and after the first dose of nivo. Peripheral blood mononuclear cells were isolated, enriched for CD8+ T cells and using the 32-plex IsoCode technology, single-cell cytokine signals were captured and polyfunctional strength of CD8+ T cells was evaluated across four groups (effector, stimulatory, regulatory, inflammatory). A comparison analysis was performed between pre- and post- nivo treatment and between patients who relapsed (non-responders) vs those who did not (responders). Results: Thirty-three of 39 planned patients have been enrolled, of which 28 are evaluable and 5/28 (18%) developed recurrence. Median age is 68 years (range 51-85), 9/28 (32%) patients are female, 26/28 (93%) are white, disease sites include oropharyngeal 6/28 (21%), oral cavity 11/28 (39%) and larynx 11/28 (39%). Samples were evaluated at a median follow up of 5.9 months from enrollment. Single-cell analysis demonstrated a strong upregulation of polyfunctional human CD8+ T cell subsets in responders. Polyfunctional Strength Index (PSI) was enhanced in CD8+ T cells across the responders’ samples, composed largely of effector cytokines (granzyme-β, IFN-γ, MIP-1α, perforin, TNF-α). Conclusions: Single-cell functional proteomic analysis revealed significantly upregulated polyfunctional profiles and an increase in effector cytokines in patients who responded to nivo. This data provides important insights into PD-1 inhibitor triggered T-cell activity and may be used to predict response to ICIs in HNSCC patients using a blood test. Clinical trial information: NCT03355560 .

6017Background: 2Despite aggressive adjuvant treatment, locally advanced HNSCC patients undergoing primary surgical resection with high risk [HR] features (extracapsular extension of lymph nodes (L...

6059Background: Immune checkpoint inhibitors have been shown to induce durable tumor response in a subset of recurrent and/or metastatic HNSCC. Higher expression of PD-L1, INF-γ, and composite sign...