Dual PD1 and CTLA4 immune checkpoint blockade and hypofractionated radiation in patients with salivary gland cancers.

6011 Background: No systemic therapy standard of care exists for recurrent/metastatic malignancies of the salivary glands (SGC) and immune checkpoint inhibitors (ICIs) have low response rates. Preclinical data in solid tumors suggest syngergistic antitumor effects of ICIs with hypofractionated radiation (XRT). This study explored the safety and activity of nivolumab (N) and ipilimumab (I)with palliative XRT. Methods: This phase I/II open label single arm trial enrolled patients (pts) with incurable SGCs (WHO 2017) with evidence of progression, ECOG 0-1, no prior antiPD1 or CTLA4 directed therapy, RECIST 1.1 measurable disease excluding the XRT site. Pts received N 3mg/kg IV Q 2 weeks x 12 doses followed by 480 mg IV Q4 weeks x 8 doses and I 1 mg/kg IV Q6 weeks x 4 doses. XRT was given to a total dose of 24Gy in 3 fractions every other day over 1 week (wk) and initiated 2 wks after the first dose of N and I. Research blood collection was obtained prior to wks 1, 8 and 16. The primary endpoint was safety and tolerability using CTCAE v. 4, secondary endpoints were objective response rates (ORR) by RECIST 1.1 criteria in non-radiated sites of measurable disease, overall survival (OS) and progression free survival (PFS). The study was approved by the FHCC IRB and registered on clinicaltrials.gov (NCT03749460). Results: Between 4/2019 and 5/2022, 20 pts were enrolled, the median age was 58 (range 27-77) years, 10 (50%) were male, 12 (60%) had ECOG 0, and 7 (35%) were Asian. Most common histologies were adenoid cystic 9 (45%) and salivary duct 4 (20%), 15 (75%) had no prior systemic therapy. Ten (50%) had both local and distant disease, 14 (70%) had commercial NGS testing, all had TMB < 10mut/Mb, MSI-stable tumors. All patients completed XRT with the most common XRT site being the lung 13(65%) and bone 7(35%). The median number of N doses received was 12 (range 3-20) and I doses 4 (range 1-4). Enrollment was halted until first 6 pts were assessed for dose limiting toxicities during initial 12 wks of treatment, none were observed. Among all pts enrolled, 5 (20%) Grade 3 AEs were observed: adrenal insufficiency, hypokalemia , lung infection, hypotension, and mania. No grade 4/5 toxicities were observed. One pt was not evaluable for RECIST 1.1 due to rapid disease progression: partial responses were observed in 4 (20%: 2 pts with salivary duct, 1 acinic cell and 1 adenoid cystic) with a median duration of 15.5 months (mos) (range 6-16 mos), stable disease in 6 (30%) all lasting 6 mos or greater, and progressive disease in 9 (45%). With a median follow-up of 16 mos, median OS was 25 mos (95% CI: [1.56, 2.59]) and median PFS was 7.2 mos (95% CI: [0.21, 1.56]). Exploratory correlative peripheral blood analysis is ongoing and will be reported. Conclusions: Nivolumab/ipilimumab and palliative XRT results in low rates of severe toxicities, modest ORR but durable ORR/SD. Further work is necessary to explore predictors for response. Clinical trial information: NCT03749460 .