Objective:

To investigate tumor heterogeneity in combined small-cell lung cancer (cSCLC) and improve diagnostic accuracy using spatial multi-omics.

Key Findings:

• cSCLC tumors show high levels of shared mutations, indicating a single-clone origin.
• Tumor components can be spatially separated or intermingled, complicating diagnosis.
• Areas with small-cell features exhibit lower immune infiltration and reduced antigen presentation.
• Fibroblast-rich bands may act as structural barriers, complicating biopsy sampling.
• The 'cSCLC Detector' assay demonstrated improved sensitivity in detecting cSCLC.

Interpretation:

The study highlights the complexity of cSCLC diagnosis due to tumor heterogeneity and suggests that molecular assays can enhance diagnostic accuracy, particularly in cases with limited biopsy samples.

Limitations:

• Study limited to 19 untreated tumors, which may not represent all cSCLC cases.
• Potential variability in assay performance across different patient populations.

Conclusion:

Molecular assays like the 'cSCLC Detector' may significantly aid in diagnosing cSCLC, especially when traditional histopathologic methods are insufficient due to small biopsy sizes.