Comparison of ASCL1, NEUROD1, and POU2F3 expression in surgically resected specimens, paired tissue microarrays, and lymph node metastases in small cell lung carcinoma

Aims Subtypes of small cell lung carcinoma (SCLC) are defined by the expression of ASCL1, NEUROD1, and POU2F3 markers. The aim of our study was to explore the extent to which the intratumoral heterogeneity of ASCL1, NEUROD1, and POU2F3 may lead to discrepancies in expression of these markers in surgical samples and their matched tissue microarray (TMA) and lymph node (LN) metastatic sites. Methods and results The cohort included 77 patients with SCLC. Immunohistochemical examinations were performed on whole slides of the primary tumour, paired TMAs, and metastatic LN sites. Samples with H‐scores >50 were considered positive. Based on the ASCL1, NEUROD1, and POU2F3 staining pattern, we grouped the tumours as follows: ASCL1‐dominant (SCLC‐A), NEUROD1‐dominant (SCLC‐N), ASCL1/NEUROD1 double‐negative with POU2F3 expression (SCLC‐P), and negative for all three markers (SCLC‐I). In whole slides, 40 SCLC‐A (52%), 20 SCLC‐N (26%), 15 SCLC‐P (20%), and two SCLC‐I (3%) tumours were identified. Comparisons of TMAs or LN metastatic sites and corresponding surgical specimens showed that positivity for ASCL1, NEUROD1, and POU2F3 in TMAs (all P