The development of therapies that target cancer stem cells (CSCs) and bulk tumors is both crucial and urgent. Several signaling pathways, like Notch and Hedgehog (Hh), have been strongly associated with CSC stemness maintenance and metastasis. However, the extensive crosstalk present between these two signaling networks complicates the development of long-term therapies that also minimize adverse effects on healthy tissues and are not overcome by therapy resistance from CSCs. The present work aims to overview the roles of Notch and Hh in cancer outburst and the intersection of the two pathways with one another, as well as with other networks, such as Wnt/β-catenin, TGF, and JAK/STAT3, and to explore the shaping of the tumor microenvironment (TME) with specific influence on CSC development and maintenance.

The incidence rate of cutaneous melanoma is on the rise worldwide, due to increased exposure to UV radiation, aging populations, and exposure to teratogen agents. However, diagnosis is more precise, and the increased number of new cases is related to the improved diagnosis tools. Despite better early diagnosis and better therapies, melanoma has remained a significant public health challenge because of its aggressive behavior and high potential for metastasis. In 2020, cutaneous melanoma constituted approximately 1.3% of all cancer deaths that occurred within the European Union, thereby highlighting the necessity for effective prevention, timely diagnosis, and sustainable treatment measures, especially as a growing number of cases occur among younger patients. Melanoma is regarded as one of the most inflamed cancers due to its high immune cell presence and strong response to immunotherapy, fueling the need for development of immune-driven innovative treatments. Approved therapies, including immune checkpoint inhibitors (e.g., anti-PD-1 and anti-CTLA-4), have notably improved survival rates in melanoma. However, the limitations of the PD-1/PD-L1 and CTLA-4 axes inhibitors, such as low response rates, treatment resistance, and toxicity, have driven the need for continued research and advancements in treatment strategies. Current clinical trials are exploring various combinations of immune checkpoint inhibitors with costimulatory receptor agonists, chemotherapy, targeted therapies, and other immunotherapies, with the goal of improving outcomes and reducing side effects for melanoma patients. Emerging approaches, including adoptive cell therapy with tumor-infiltrating lymphocytes (TILs) and oncolytic virotherapy, are showing promise. While CAR-T cell therapy has been less successful in melanoma compared to blood cancers, ongoing research is addressing challenges like the tumor microenvironment and antigen specificity. This review provides an overview of the requirement for advances in these medications, to mark a significant step forward in melanoma management, set to bring a fresh breath of hope for patients.

Relapse and metastasis are the major challenges that stand in the way of cancer healing and survival, mainly attributed to cancer stem cells (CSCs). Their capabilities of self-renewal and tumorigenic potential leads to treatment resistance development. CSCs function through signaling pathways such as the Wnt/β-catenin cascade. While commonly involved in embryogenesis and adult tissues homeostasis, the dysregulation of the Wnt pathway has direct correlations with tumorigenesis, metastasis, and drug resistance. The development of therapies that target CSCs and bulk tumors is both crucial and urgent. However, the extensive crosstalk present between Wnt and other signaling networks (Hedgehog and Notch) complicates the development of efficient long-term therapies with minimal side-effects on normal tissues. Despite the obstacles, the emergence of Wnt inhibitors and subsequent modulation of the signaling pathways would provide dynamic therapeutic approaches to impairing CSCs and reversing resistance mechanisms.