Immunotherapy in small-cell lung cancer: from molecular promises to clinical challenges

Management of small cell lung cancer (SCLC) has not changed over the last decades. In more recent years, alterations of DNA repair machinery and other molecular pathways have been identified in SCLC and preclinical data suggest that dysregulation of these pathways might offer new therapeutic opportunities.

While immune checkpoint inhibitors (ICIs) have had a major impact on the clinical outcome of several solid tumors, including non-small cell lung cancer, the potential role of ICIs is currently under investigation in SCLC and some promising data are available. However, several clinical and biological hurdles have to be overcome and predictive markers are still eagerly needed. Knowledge of molecular pathways specifically involved in SCLC growth and treatment resistance is essential for a more rational planning of new combinations including ICIs.

The present manuscript summarizes the current clinical evidence on immunotherapy in SCLC, describes the molecular bases underlying treatment resistance and discusses the potentialities and the rationale of different therapeutic combinations.

The role of immune microenvironment in small-cell lung cancer: Distribution of PD-L1 expression and prognostic role of FOXP3-positive tumour infiltrating lymphocytes

INTRODUCTION

The prognosis of small-cell lung cancer (SCLC) is dismal and new effective therapies are needed. Immunotherapy looks promising, but no molecular predictive markers are currently available, and data on immune microenvironment are very limited.

METHODS

We retrospectively analysed 104 SCLC cases. Immunohistochemistry evaluation of PD-L1 was performed both on tumour cells (TCs) and on tumour-infiltrating immune cells (TIICs) by using anti-PD-L1 22C3 antibody (DAKO) and categorised by using 1% as cut-off point. Tumour-infiltrating lymphocytes (TILs) were characterised by using anti-CD8 and anti-FOXP3 antibodies. Semi-quantitative score was used and categorised as positive versus negative/low. The relation of molecular markers with prognosis and with clinical variables was evaluated.

RESULTS

The analysis included 66 stage I-III patients (48 surgically resected, 18 treated with radical-intent chemoradiotherapy) and 38 metastatic cases. In the overall study population, PD-L1 was expressed on TCs and TIICs in 25% and 40% of cases, respectively. The proportion of PD-L1-positive cases was significantly higher in stage I-III versus metastatic patients (32% versus 13%, p: 0.034 for TCs; 51.5% versus 21% for TIICs, p: 0.002). CD8- and FOXP3-positive TILs were present in 59% and 72% of samples, respectively. The presence of FOXP3-TILs was associated with improved prognosis among non-metastatic patients, with a hazard ratio for survival of 0.32 (95% confidence interval [CI]: 0.16-0.7, p: 0.006) for univariate analysis, and 0.37 (95% CI: 0.17-0.81, p: 0.013) for multivariate analysis.

CONCLUSIONS

Immune contexture of SCLC may differ according to stage. The presence of FOXP3-positive TILs is a potential prognostic marker for stage I-III SCLCs and warrants further investigation.