The Future of Immunotherapy Targets

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Immunotherapy, in the form of immune checkpoint inhibitors (ICI), has been a recent breakthrough in the management of both early and late-stage melanoma. With the advent of immunotherapy, the 1-year survival rate for patients with metastatic disease has increased from 25% to 50%.¹ ICIs have contributed to improved outcomes of treatment and prognosis of patients with different malignancies and are now served as a standard treatment for advanced melanoma.² 

Recent study results revealed that treatment with combined anti-CTLA-4/anti-PD-1 results in median overall survival and a significant durability response, which is superior to that of nivolumab monotherapy and ipilimumab monotherapy.³ Also, the benefits of combined treatment were similar for patients, irrespective of their BRAFV600 mutational and PD-L1 expression status. ICIs provide a significant response in patients with brain metastasis, particularly those who are asymptomatic of malignant infiltration at the time of presentation.⁴ Study results also revealed that intracranial responses of combined ipilimumab/nivolumab were more than 50% in patients whose metastases have not been treated with brain radiotherapy.⁵ Another study found that ipilimumab/nivolumab was significantly superior to nivolumab monotherapy with a 5-year survival rate of 51% in patients with asymptomatic disease.⁶ In the therapeutic field of melanoma, prior immunostimulatory treatments such as interleukin-2 (IL-2) were superseded by ICIs. For high-risk, early-stage melanoma, ipilimumab was found to increase the 3-year recurrence-free rate by more than 10%.⁶ 

While surgical excision is the primary treatment for non-melanoma skin cancers (NMSCs), immunotherapy has emerged as a promising treatment option in recent years.⁷ In the case of NMSCs, ICIs are the most commonly used immunotherapy drugs. These drugs block proteins in cancer cells, preventing the immune system from recognizing and attacking them.⁸ Clinical trials have shown that ICIs such as pembrolizumab and nivolumab have high response rates and durable responses in patients with advanced NMSCs.⁹ These drugs have been approved by the US Food and Drug Administration for the treatment of metastatic or locally advanced squamous cell carcinoma (SCC) and basal cell carcinoma (BCC), which cannot be treated with surgery or radiation. Other types of immunotherapies for NMSCs include topical immunomodulators such as imiquimod and ingenol mebutate, which stimulate the immune system to attack cancer cells locally.¹⁰ Intralesional immunotherapy, which involves injecting an immune-stimulating substance directly into the tumor, is also being investigated as a potential treatment option. For the treatment of cutaneous SCC (cSCC), pembrolizumab and cemiplimab, two single-agent anti-PD-1 inhibitors, exhibited an overall response rate of 42% and 52% in recurrent/metastatic disease and locally advanced disease, respectively, when used as frontline, first-line treatment for advanced or metastatic cSCC that is not responsive to surgery or radiation.¹¹ Both medications had long-lasting effects with manageable side effects. Merkle cell carcinoma (MCC), like cSCC, is a very immunogenic illness and a promising target for immunotherapy based on ICI. In pre-treated patients with advanced MCC, the JAVELIN Merkel 200 study showed that avelumab resulted in a 33.0% overall response rate and a median duration of response of 40.5 months.¹² In comparison to cSCC, BCCs are at least two times more prevalent. The metastatic rate for BCCs is less than 1%, which is substantially lower than that for cSCCs and MCCs. Moreover, cemiplimab has been shown to generate a strong antitumor response in patients with locally advanced BCC.¹³

Biomarkers of response to immunotherapy in melanoma have been studied to help identify patients most likely to benefit from treatment and develop new therapeutic strategies. Programmed death-ligand 1 (PD-L1) is a protein expressed on the surface of some cancer cells, including melanoma.¹⁴ It interacts with the programmed death-1 (PD-1) receptor on T cells, inhibiting their activity and preventing the immune system from attacking cancer cells. Tumors with high levels of PD-L1 expression are more likely to respond to PD-1/PD-L1 checkpoint inhibitors. Tumor mutational burden (TMB) measures the number of mutations present in a tumor's DNA. High TMB is associated with an increased likelihood of response to ICIs, as these mutations may generate new tumor antigens that can be recognized by the immune system.¹⁵ TMB is naturally elevated in melanoma and correlates with better responses to immune checkpoint inhibition depending on the severity of cancer. However, it is not regularly used as a predictor of ICI response. Melanoma responds exceedingly well to ICI; hence, a biomarker of ICI resistance may be more important than a biomarker of response in clinical care. Tumor-infiltrating lymphocytes (TILs) are immune cells that have migrated into the tumor microenvironment. Tumors with high levels of TILs are more likely to respond to immunotherapy, as they indicate an ongoing immune response against the tumor.¹⁶ The biomarkers of immunotherapy response in melanoma also include immune gene expression profiling and the gut microbiome. Gene expression profiling can be used to assess the activity of immune-related genes within the tumor microenvironment.¹⁷ Certain gene signatures have been associated with response to immunotherapy in melanoma. The composition of the gut microbiome has been shown to affect the efficacy of immune checkpoint inhibitors.¹⁸ Studies suggest that a more diverse gut microbiome is associated with a better response to immunotherapy.

Biomarkers that can help predict immunotherapy response or resistance in non-melanoma skin cancers include Interferon-gamma (IFN-γ) signature, Immunoscore, and Circulating tumor DNA (ctDNA). Interferon-gamma (IFN-γ) signature is a cytokine that plays a vital role in activating the immune system.¹⁹ Tumors with a high IFN-γ signature may be more likely to respond to immunotherapy. The Immunoscore is a measure of the immune cell infiltration and activation within a tumor. A higher Immunoscore may indicate a better response to immunotherapy.²⁰ Circulating tumor DNA (ctDNA) refers to small fragments of DNA that are shed by tumor cells into the bloodstream. The presence of ctDNA may indicate the presence of residual disease, and monitoring ctDNA levels may help predict response to immunotherapy.²¹ 

Immunotherapy has revolutionized the treatment of melanoma and non-melanoma skin cancers, and research is ongoing to identify new targets and improve existing therapies. Now considered the gold standard for treating advanced melanoma, immune checkpoint inhibitors (ICIs) have helped improve the treatment and prognosis of patients with a variety of cancers. Median overall survival and a substantial, durable response are achieved with anti-CTLA-4/anti-PD-1 combination therapy. Previous immunostimulatory therapies, such as interleukin-2 (IL-2), have been replaced by immune checkpoint inhibitors in the therapeutic field of melanoma. Patients with advanced NMSCs have shown both a high response rate and long-lasting responses to immune checkpoint inhibitors like pembrolizumab and nivolumab, according to clinical trials. Immunotherapy has been shown to be effective against melanoma, and researchers have been looking at biomarkers of response to better target treatment towards patients suffering from skin cancers. PD-L1 expression, TMB, MSI, TILs, and HPV status have all been identified as potential biomarkers of response to immunotherapy in melanoma and non-melanoma skin cancers. However, additional research is needed to better understand the complex interplay between the tumor microenvironment and the immune system.

References

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