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Background: Small cell lung cancer (SCLC) is the most aggressive neuroendocrine lung cancer, with a dismal 5‐year survival rate. No reliable biomarkers or imaging are available for early SCLC detection. In a search for a specific marker of SCLC, this study identified that hepatocyte cell adhesion molecule 2 (HEPACAM2), a member of the immunoglobulin‐like superfamily, is highly and specifically expressed in SCLC. Methods: This study investigated HEPACAM2 expression in patients with SCLC via RNA sequencing and evaluated its relationship to progression‐free survival (PFS) and overall survival (OS). Immunofluorescence microscopy was used to assess the cellular location of HEPACAM2 and to conduct in vitro and in vivo studies to understand its expression and functional significance. These findings were integrated with databases of patients with SCLC. Results: HEPACAM2 is highly expressed and specific to SCLC. HEPACAM2 levels are inversely correlated with PFS and OS in patients with SCLC and are expressed at all stages. Moreover, HEPACAM2 messenger RNA and its peptides can be detected in the secretomes in cell lines. Positively correlated with ASCL1 expression in SCLC tumors, HEPACAM2 is localized primarily to the plasma membrane and linked to extracellular matrix signaling and cellular migration. A loss of HEPACAM2 in SCLC cells attenuated ASCL1 and MYC expression. Consistent with clinical data, in vitro and in vivo studies suggested that HEPACAM2 promotes cancer cell growth. Conclusions: With its remarkable specificity, high expression, presence in early disease, and extracellular secretion, HEPACAM2 could be a potential diagnostic cell surface biomarker for early SCLC detection. These findings warrant further investigation into its role in the pathobiology of SCLC. Hepatocyte cell adhesion molecule 2 (HEPACAM2) shows great promise as a diagnostic biomarker for small cell lung cancer (SCLC) due to its high specificity, strong expression in SCLC tissues, and extracellular secretion, which make it an ideal candidate for early detection. As a cell surface protein, HEPACAM2 offers the potential for minimally invasive diagnostic approaches to improve SCLC screening and early intervention strategies. [ABSTRACT FROM AUTHOR]

Antibody-drug conjugate (ADC) therapy has transformed treatment for several solid tumors, including small cell lung cancer (SCLC). However, significant challenges remain, including systemic toxicity, acquired resistance, and the lack of reliable biomarkers for patient selection. To enhance the effectiveness of ADC therapies in SCLC, we focused on target selection in this study by investigating the expression of ADC targets - SEZ6, DLL3, CD276, and TACSTD2 - in cell lines and patient samples. SEZ6 expression was significantly elevated in various SCLC transcriptional subtypes, particularly ASCL1, and exhibited gender-specific differences, being lower in women. DLL3 was primarily observed in the ASCL1 subtype, while CD276 showed high expression in non-neuroendocrine subtypes. TACSTD2 levels were generally low and attenuated in lymph nodes and brain metastases compared to primary tumors. Our findings underscore the importance of understanding target expression patterns to optimize ADC therapy and advance precision medicine in SCLC treatment. [ABSTRACT FROM AUTHOR]