Frequency of mitogen-activated protein kinase and phosphoinositide 3-kinase signaling pathway pathogenic alterations in EUS-FNA sampled malignant lymph nodes in rectal cancer with theranostic potential

Background: Targeted next-generation sequencing has the potential to stratify a tumor by molecular subtype and aid the development of a biomarker profile for prognostic risk stratification and theranostic potential. Objective: To assess the frequency and distribution of pathogenic alterations in malignant lymph node cytology specimens. Design: Multigene molecular profiling of archived malignant EUS-FNA lymph node cytology specimens using the Ion Ampliseq Cancer Hotspot Panel v2, which targets at least 2855 possible mutations within 50 cancer-associated genes. Setting: Single tertiary referral center. Patients: Sporadic, treatment naive, locally advanced primary rectal cancer by EUS-FNA (n = 76) who subsequently completed neoadjuvant therapy with on-site oncologic surgery. Main Outcome Measurements: The frequency and distribution of pathogenic alterations in malignant lymph node cytology specimens by the mitogen-activated protein kinase (MAPK) or phosphoinositide 3-kinase (PI3K) signaling pathways, by KRAS or NRAS wild-type lymph node status, by extramesenteric lymph node status, and by a complete pathologic response status. Results: Eleven patients (14.5%) were 50-gene panel wild-type. Sixty-five patients had 139 pathogenic alterations (2 [1-3] per patient) in 13 of 50 evaluated genes. The following represent a spectrum of identified alterations: TP53 (n = 52; 68.4%), APC (n = 36; 47.4%), KRAS (n = 22; 28.9%), FBXW7 (n = 8; 10.5%), NRAS (n = 6; 7.9%), PIK3CA (n = 4; 5.3%), SMAD4 (n = 3; 3.9%), and BRAF (n = 3; 3.9%). Pathogenic alterations were identified in the MAPK and PI3K signaling pathways in 41% and 5% of patients, respectively. Limitations: Findings were limited to a 50 cancer-associated gene analysis. Conclusions: Molecular EUS lymph node assessments using cancer "hotspot" panels can identify pathogenic alteration frequency and distribution and have theranostic potential for individualized patient care.