Phenotypic Landscape of Pulmonary Neuroendocrine Tumors: Subtyped by OTP/ASCL1 Expression Correlated with Histology, Hormones and Outcome

Recent studies have shown that pulmonary neuroendocrine tumor (NET) subgroups, defined by the transcription factors OTP and ASCL1, correlate with age, sex, and tumor location. Their relationships with histology and hormone production, however, remain unclear. We analyzed 170 pulmonary NETs classified by OTP (O) and ASCL1 (A) expression into four groups: O + /A + , O + /A-, O-/A + , and O-/A-. Subgroups were assessed for histology, hormone expression, therapy-related markers, outcomes, and matched metastases. Among 152 resected primaries, O + /A + tumors (38%) were most frequent, occurring mainly in females (median age 72 years), and typically showed central or peripheral location, solid/spindle morphology with diffuse gastrin-releasing peptide (GRP), and focal ACTH/calcitonin. They also showed strong DLL3 expression and pronounced neuroendocrine cell hyperplasia. O + /A- tumors (23%) occurred predominantly in females (median age 56 years) with solid/trabecular patterns, occasional/ACTH, and strong SSTR2A/5 expression. O-/A- tumors (25%) were more common in males (median age 70 years), often central with solid/trabecular or oncocytic histology, serotonin expression (24%), and frequently SSTR2A-positivity. O-/A + tumors (14%) occurred across both sexes (median age 58 years), were centrally located, and solid, sometimes oncocytic features with moderate DLL3/SSTR2A expression. Metastases mirrored their primaries in transcription factor and hormone profiles. In the univariate analysis, OTP-negative tumors were associated with poorer disease-free survival (DFS). However, the multivariate analysis identified Ki67-based WHO grades (G1-G3) as the only independent prognostic factors. In conclusion, integrating OTP and ASCL1 refines pulmonary NET classification into four histologically and biologically distinct subgroups, providing additional insight into tumor heterogeneity. O + /A + tumors showed solid-spindle features and diffuse GRP and frequent ACTH expression, trabecular patterns characterized ASCL1-negative tumors, while oncocytic histology predominated in OTP-negative tumors, highlighting their role in defining tumor heterogeneity.