Molecular Characterization of Null-type Large Cell Carcinoma Identified an Adenocarcinoma-related Subtype Associated to Inflammatory Carcinogenesis

Background: According to the current World Health Organization Classification of Thoracic Tumors, Large Cell Carcinoma (LCC) are an undifferentiated non-small cell carcinoma (NSCLC) that lacks the cytological, architectural, immunohistochemical, and histochemical features of small cell carcinoma, adenocarcinoma, or squamous cell carcinoma (SCC). Limited data exist concerning molecular and immunophenotypic markers able to offer specific diagnostic characterization and definition and identify possible therapeutic targets. Therefore LCC remain an orphan entity whose diagnosis is made only by exclusion. Design: A retrospective series of surgical specimens of 28 LCC potential candidate from 3 three Italian institution were reviewed in terms of morphology and immunohistochemical features. Confirmed marker-null LCC were assessed for alterations in 409 genes and transcriptomic profiling of 20,815 genes. Immunohistochemical stainings were done to validate molecular findings. Results: Marker-null LCC was confirmed in 16 patients. Genes frequently altered included TP53 (14/16; 87.5%), RB1 (5/16;31.3%) and KEAP1 (4/16; 25.0%). Comparison of LCC transcriptomes with 17 ADC and 11 LCNEC pure histology lung cancers showed that LCC constituted a standalone cluster except for 5 samples included in cluster enriched for ADC histology samples and therefore called adenocarcinoma-like LCC (ADLike). LCC cluster showed overexpression of different genes involved in ATR pathways, DNA repairs and biological processes related to proliferation and cell division. In addition Pou2f3 and Foxi1 were distinctive overexpressed markers in this cluster. On the contrary ADLike LCC showed low tumor mutational load, stable chromosomal asset and positive association with AIM2 inflammasome complex and other pathways related to the inflammatory response. Conclusions: LCCs were single standalone entity with presence of an ADLike subgroup. Our findings support differential markers in the FOXI1, POU2F3 and AIM2 genes, which could be useful in routine diagnostic immunohistochemical staining and offer new perspectives in the therapeutic approaches for this rare disease.