Jeng-Lin, Daniel

6057 Background: The incidence rate of human papillomavirus associated oropharyngeal squamous cell carcinoma (HPV(+)OPSCC) has persistently increased over the past decade and is anticipated to rise further over the next decade. Cost effective, accurate, and less invasive screening options for HPV(+)OPSCC have remained stagnant leading to the interrogation of circulating tumor DNA in liquid biopsies such as plasma. We hypothesized that candidate methylated DNA markers (MDMs), previously described by our group, would be present in the plasma of patients with HPV(+)OPSCC and absent in controls. Methods: HPV(+)OPSCC cases were enrolled from a high-volume referral practice. Cancer-free control patients were identified from the surrounding 7-county catchment area and frequency matched to cases by age and alcohol use. cfDNA was extracted from 4 mL of plasma and bisulfite converted prior to Target Enrichment Long-probe Quantitative Amplified Signal assays for 15 MDMs. Strand counts for individual MDMs were normalized to a methylated genomic reference marker. An MDM score was derived via random forest modeling of the 15 MDMs. Area under the receiver operator characteristic curve (AUC) for discriminating cases from controls was evaluated for individual markers and for the MDM score. The sensitivity of the MDM score at 95% specificity was also evaluated. Results: The study consisted of 96 HPV(+)OPSCC and 100 cancer-free controls. The study population was predominately white (95%) with a median age of 61 yrs (IQR: 52-69 yrs). Eighty-nine percent of the cases were male with cancers affecting either the tonsil in 50 (52%) or base of the tongue in 46 (48%) patients; by design 50% of controls were male. Stage I:II:III:IV disease was present in 66%:22%:9%:3% of the cases. The median (IQR) AUC across the 15 MDMs was 0.83 (0.82-0.85) overall: 0.78 (0.77-0.83) for stage I disease and 0.92 (0.91-0.93) for stage II-IV disease. The MDM score for the combined panel of 15 MDMs achieved a cross-validated AUC of 0.93 (CI: 0.89-0.97) overall: 0.90 (CI: 0.84-0.96) for stage I disease and 0.98 (CI: 0.97-1.00) for stage II-IV disease. At 95% specificity, the cross-validated sensitivity of the MDM score for HPV(+)OPSCC was 80% (CI: 71-87%) overall: 73% (CI: 60-83%) for stage I disease and 94% (CI: 78-99%) for stage II-IV disease. Conclusions: We validated a set of previously discovered MDM markers in HPV(+)OPSCC in a robust case control cohort using plasma. The MDMs were detected in both early and late-stage disease. Additional prospective studies in larger intended use cohorts are needed to validate our results for clinical use.

6061 Background: PDS0101 is a T cell stimulating immunotherapy (therapeutic vaccine) targeting HPV16. The combination of PDS0101 + pembrolizumab (5 cycles) has shown durable clinical responses in HPV-positive recurrent/metastatic HNSCC. MC200710 is a window of opportunity study in patients with HPV-associated oropharyngeal squamous cell carcinoma (HPV+ OPSCC). This prospective phase II trial utilized 2 cycles of neoadjuvant PDS0101 aloneor in combination with pembrolizumab prior to surgical resection or chemoradiotherapy (CRT). Herein, we report the initial results, including primary endpoint of ctDNA response. Methods: Between June 2022 and September 2024, 20 patients (10 per Arm) with locally advanced HPV+ OPSCC were enrolled in a sequential alternating design. Arm A received 2 cycles of PDS0101 and Arm B received 2 cycles of PDS0101 and pembrolizumab with all patients undergoing subsequent surgery or CRT. Assessments were done at baseline, post cycle 1, and post cycle 2 (prior to surgery or CRT). The coprimary endpoint of ctDNA response was defined as a ≥50% decline in ctDNA post cycle 2 compared to baseline as quantified using NavDx (TTMV fragments/mL). Radiologic objective response rate (ORR) was assessed as per RECIST 1.1. Toxicity through the neoadjuvant period was assessed using CTCAE criteria and recurrence rates following surgery or CRT are reported. Results: Patients were similar between arms: male 90%, median age 61 years, cT1/T2 70%, cN1 65%, and no smoking history 65%. All patients completed both cycles of therapy with 13 (65%) undergoing primary operative management and 7 CRT (35%). The most common toxicity was injection site reaction 85% grade 1, 15% grade 2, 0% grade 3, consistent with prior studies. One patient experienced grade 2 pneumonitis during the neoadjuvant window (Arm B). There was one grade 3 toxicity (5%) possibly attributable to study intervention with one patient experiencing transient hepatitis requiring hospitalization (Arm A). Zero of 10 patients in Arm A had a ≥50% decline in ctDNA from baseline while 5 of 10 patients (50%) met this primary endpoint in ARM B (p=0.03). After Cycle 2, based on RECIST 1.1, no Arm A patients had a partial response (PR), with 7 having stable disease (SD); Arm B had 2 patients with PR and 8 with SD. With median follow up of 6 months, 2 patients in Arm A recurred and 0 patients in Arm B. Conclusions: The combination of PDS0101 and pembrolizumab met the trial’s primary endpoint of ctDNA response and shows promise for further evaluation. ctDNA can be used to assess early response and future studies could use ctDNA to adapt neoadjuvant therapy. Based on these findings, a neoadjuvant dose optimization study in HPV16+ oropharyngeal carcinoma is warranted and evaluation of PDS0101 and pembrolizumab in comparison to pembrolizumab alone. Clinical trial information: NCT05232851 .

6049 Background: In the head and neck, human papillomavirus-related oropharyngeal squamous cell carcinoma (HPV(+)OPSCC) has a better prognosis and more tumor infiltrating lymphocytes (TILs) compared to its HPV(-) counterpart. Within HPV(+)OPSCC, the prognostic value of TILs in the primary tumor and in metastatic lymph nodes is not well understood. Methods: This is a matched case-control study at a tertiary care center of HPV(+)OPSCC patients who underwent primary surgery between 05/2007–12/2016. Cases developed locoregional recurrence or distant metastases during follow-up, while controls did not during a similar duration of follow-up. Pairs were matched on age, American Joint Committee on Cancer (AJCC) 8th edition pathologic stage, sex, year of surgery, degree of adjuvant treatment, comorbidities, and smoking status. One representative H&E slide of the primary tumor and lymph node (when nodal disease was present) from each patient was independently reviewed by two pathologists (JG, MR) blinded to outcome, for tumor TILs (tTILs) density (defined as % TILs), presence/absence of desmoplastic stroma, and when stroma was present, for stromal TILs (sTILs) density (defined as relative crowding of TILs). The Brandwein-Gensler pattern of invasion (POI) score was used to grade the primary tumor. Interrater agreement was assessed using Cohen’s kappa. Associations between TILs and time to disease progression were assessed using Cox proportional hazards regression models. Results: 41 case-control pairs (N=82) were included in the study: 38 (46%) were AJCC pStage I, 37 (45%) were pStage II, and 7 (9%) were pStage III; 22 (27%) underwent surgery alone, 15 (18%) underwent surgery with adjuvant radiotherapy, and 45 (55%) underwent surgery with adjuvant chemoradiation. Interrater agreement was fair for tTILs density in the primary tumor ( k=0.24) and lymph node ( k=0.23), moderate for desmoplastic stroma in the primary tumor ( k=0.58) and lymph node ( k=0.64), moderate for sTILs density in the primary tumor ( k=0.58) and lymph node ( k=0.48), and fair for the POI score ( k=0.17). tTILs density ≥10% (HR 0.35, 95% CI 0.14-0.90, p=0.028) and a moderate/dense sTILs density (HR 0.15, 95% CI 0.04-0.68, p=0.014) in the primary tumor were significantly associated with decreased risk of disease progression. An aggressive POI score of III or IV was significantly associated with increased risk of disease progression (HR 4.00, 95% CI 1.34-11.96, p=0.013). None of the study measures in the lymph node were significantly associated with disease progression. Conclusions: In HPV(+)OPSCC, a higher density of tumor and stromal TILs and nonaggressive POI in the primary tumor specimen may indicate a lower risk of disease progression. TILs may serve as a powerful prognostic marker for the adaptive immune response to this disease.