Long term outcomes in patients with recurrent/metastatic (R/M) salivary gland cancer (SGC) treated with immune checkpoint inhibitors (ICI).

Abstract

e18063 Background: There is no standard of care systemic therapy in R/M SGC. Regimens containing ICIs are of interest, but overall response rates (ORRs) are low, and median duration of response (mDOR) and long term overall survival (OS) data are limited. We pooled mature data from two clinical trials evaluating the use of ICIs in SGC to evaluate long term outcomes. Methods: We combined the results of two phase I/II, open label, single arm trials utilizing ICIs in R/M SGC. NCT02538510 administered pembrolizumab 200 mg IV q3 weeks and vorinostat 400 mg PO 5 days on/2 days off. NCT03749460 administered nivolumab 3mg/kg IV q2 weeks x 12 doses, followed by 480 mg IV q4 weeks x 8 doses and ipilimumab 1 mg/kg IV q6 weeks x 4 doses with hypofractionated radiotherapy at 1-5 metastatic sites to a total dose of 24Gy/3 fractions over 1 week initiated 2 weeks after immunotherapy. All patients were ≥18 years with R/M disease, evidence of progression within 3 months of study entry, measurable disease per RECIST 1.1, EGOG PS 0-1, and adequate organ function at enrollment. PDL1 expression was not required for participation and prior ICI was not allowed. ORRs were evaluated by RECIST 1.1. OS and progression free survival (PFS) were estimated via the Kaplan-Meier method. Results: 45 patients were enrolled in the two studies from 11/2015-5/2022. The combined median age was 57 (IQR 46, 66). 26 (57.8%) were male; 33 (73.3%) were white and 10 (22.2%) were Asian. 27 (60.0%) had an ECOG PS of 0. Most common histology types were adenoid cystic carcinoma (21, 46.7%), acinic cell carcinoma (5, 11.1%), and salivary duct carcinoma (5, 11.1%). The ORR was 17.8% with all responders having a PR (n=8, histology types: 3 acinic cell, 2 adenoid cystic, 1 adenocarcinoma, 1 salivary duct, 1 lymphoepithelioma-like carcinoma). 20 (44.4%) had SD, with 16 (80.0%) of these responses lasting greater than 6 months. 16 (35.6%) had PD. One patient was not evaluable for RECIST due to rapid disease progression and death. At analysis, median follow up was 29.2 months (IQR 27.1-50.0) among survivors, mDOR was 26.7 months (range 7.1-69.5+), with three patients with ongoing response. Median OS and PFS were 25.4 (95% CI 14, 43.2) and 6.2 months (95% CI 3.9, 15.5) respectively. 23 (51.1%) patients received systemic therapy after trial ICI. Patients received: 4 additional ICI (3 PD-1 monotherapy, 1 ipi/nivo), 5 androgen deprivation therapy, 5 chemotherapy, 9 other treatments (dabrafenib/trametinib, everolimus, fam-trastuzumab deruxtecan, osimertinib, lenvatinib, investigational agents). Conclusions: Although SGC is heterogenous, responses to ICI were observed in multiple subtypes and were durable, similar to observations in other solid tumors. A significant proportion received subsequent lines of therapy post ICI, and exploration of ORR and PFS to next lines of therapy is of interest. Clinical trial information: NCT02538510 and NCT03749460 .