A recent study published in Scientific Reports has shed light on three distinct molecular subtypes of small cell lung cancer (SCLC) and particular gene mutations that may affect how teh disease progresses.

While SCLC prognosis is generally poor, with only about a third of cases being curable, immune checkpoint inhibitors have provided some optimism for future treatments. Current immunotherapy options include atezolizumab (Tecentriq; Genentech) for extensive-stage SCLC (ES-SCLC), Durvalumab (Imfinzi; Astrazeneca) for ES-SCLC and, most recently, for limited-stage SCLC.

According to the researchers, “Currently, the most urgent need is to identify stable prognostic molecular markers and develop therapeutic strategies for patients most likely to respond to treatment, thereby enabling more patients to benefit from antitumor immunotherapy.”

The research team analyzed over 500 SCLC samples, using whole-exome sequencing on 200 and targeted sequencing on 313.

The analysis revealed five mutational signatures. Though, a clustering analysis indicated that the most notable distinction occurred with three clusters. Among these, the smoking-related SBS4 mutational signature was associated with the worst prognosis, even after adjusting for other factors (HR, 1.63; 95% CI, 1.01-2.36; P = .029). This cluster also exhibited the lowest tumor mutational burden (TMB) compared to the other subtypes (Wilcoxon rank-sum test P < .001), suggesting potential resistance to immunotherapy.

Conversely, patients with an SBS13 signature may respond better to immunotherapy. The SBS13 signature was linked to a more favorable prognosis and higher TMB, and has previously been associated with improved response to anti-programmed death 1 treatment in other cancers.

Limitations and Considerations

The researchers acknowledged that while they accounted for various patient and disease factors,such as age,gender,disease stage,and sample type,other potential confounders could not be accounted for. These include variations in chemotherapy, radiotherapy, and immunotherapy combinations, as well as undetected comutations or genetic alterations that could impact tumor biology and treatment response. Lifestyle factors, such as smoking habits and exposure to carcinogens, may also play a role.

“Currently, the most urgent need is to identify stable prognostic molecular markers…”

Further analysis of specific mutations associated with prognosis revealed that among 38 high-frequency mutations, only one, UNC13A, was associated with a favorable prognosis. The survival benefit seen with UNC13A mutations was attributed to an activated immune microenvironment and immune response pathways.

The authors noted, “Recent studies have demonstrated close relationships of single-gene mutations with high immunogenicity and immunotherapy efficacy, such as FAT1, TP53, MUC16 and POLE. Therefore, UNC13A mutations may serve as a potential indicator of response to immunotherapy in SCLC. Prospective cohorts are needed to confirm these findings.”

Among the other mutations studied, TP53 splice mutations were linked to a worse prognosis, even after accounting for confounders (HR, 4.20; 95% CI, 1.08-16.30; P = .043). TP53 is a known driver of SCLC, and mutations in this gene have previously been identified as an indicator of poorer survival in these patients.

the researchers stated, “this study identified several molecular markers related to SCLC prognosis by integrating somatic mutation profiles, mRNA transcriptome data, and clinical information. At the same time, we clarified underlying molecular immunological characteristics and provided clues for the growth of SCLC clinical trials and the updating of treatment methods.”