905P - Validation of MYC/TP63 classification for adenocystic carcinomas of salivary glands

Background

ACC's most characteristic chromosomal rearrangement is MYB proto-oncogene transcription factor (MYB)- or MYBL1- nuclear factor I/B (NFIB) gene fusions. Recently, two MYB-fusion agnostic subtypes, ACC-I and ACC-II, with direct prognostic and therapeutic implications have been delineated (Ferragotto R et al). Assessment of MYC and TP63 by immunohistochemistry (IHC) accurately stratifies tumors by subtype. In the present study, we aimed to validate MYC/p63 classification in a cohort of 50 ACC.

Methods

We included 50 patients diagnosed with ACC in the head and neck region and treated between 2000 and 2021 in 4 tertiary referral centers in Greece. Patients’ records were reviewed to collect demographic data (primary tumor site, age at diagnosis, sex) and disease characteristics (pathology, staging, treatment strategies, time to progression, survival). The expression of MYC and p63 were assessed by IHC. Survival analysis was performed using the Kaplan-Meier curves, and survival comparisons were performed using the Wilcoxon test. The significance level (α) was set to 5%; thus p-value< 0.05 was considered statistically significant.

Results

Based on MYC and p63 expression, 8 cases were classified as ACC-I and 39 as ACC-II. Table I shows statistically significant differences between the ACC-I and ACC-II patients. A trend was observed between mDFS for patients with ACC-I and ACC-II (41 vs 118 months, respectively, p=0.0542). Importantly, we found a statistically significant difference in mOS between the two groups (50 months for ACC-I vs. 135 months for ACC-II, p=0.0066), suggesting a more favorable prognosis for ACC type II. Table: 905P