Immune checkpoint inhibitors are a type of medication used in cancer treatment. They work by helping the body’s immune system recognize and attack cancer cells. Normally, cancer cells can hide from the immune system, but these inhibitors block certain proteins that prevent the immune system from seeing the cancer. This allows the immune system to do its job and fight the cancer more effectively.

Carbon ion radiotherapy is a special type of radiation treatment that uses carbon ions instead of the usual X-rays. This therapy is more precise and can target cancer cells more accurately, causing less damage to the surrounding healthy tissue. It is particularly useful for treating cancers that are difficult to reach or resistant to conventional radiation therapy. In this trial, carbon ion radiotherapy is combined with immune checkpoint inhibitors to enhance the overall treatment effect.

Unresectable or metastatic melanoma – Melanoma is a type of skin cancer that begins in the melanocytes, which are the cells responsible for producing melanin, the pigment that gives skin its color. When melanoma becomes unresectable, it means that it cannot be removed completely through surgery. Metastatic melanoma occurs when the cancer spreads from its original site to other parts of the body, such as the lymph nodes, liver, lungs, or brain. The disease progresses as cancer cells invade nearby tissues and organs, leading to the formation of new tumors. This spread can occur through the lymphatic system or the bloodstream. As the disease advances, it can affect the function of the organs involved.

Locally advanced or metastatic urothelial carcinoma – Urothelial carcinoma is a cancer that originates in the urothelial cells lining the bladder, ureters, and other parts of the urinary tract. When it is locally advanced, the cancer has spread beyond the inner lining of the bladder to nearby tissues or lymph nodes. Metastatic urothelial carcinoma indicates that the cancer has spread to distant organs, such as the liver, lungs, or bones. The progression involves the growth and spread of cancer cells, which can lead to the formation of new tumors in other parts of the body. This spread can occur through the lymphatic system or the bloodstream. As the disease progresses, it can impair the function of affected organs.

Locally advanced or metastatic non-small cell lung cancer (NSCLC) – Non-small cell lung cancer is a group of lung cancers that behave similarly and are the most common type of lung cancer. Locally advanced NSCLC means the cancer has spread to nearby tissues or lymph nodes but not to distant parts of the body. Metastatic NSCLC indicates that the cancer has spread to distant organs, such as the brain, liver, or bones. The disease progresses as cancer cells grow and invade surrounding tissues, forming new tumors. This spread can occur through the lymphatic system or the bloodstream. As the disease advances, it can affect the function of the organs involved.

Untreated recurrent/metastatic head and neck squamous cell carcinoma (HNSCC) – Head and neck squamous cell carcinoma is a type of cancer that arises from the squamous cells lining the moist surfaces inside the head and neck, such as the mouth, throat, and nose. Recurrent HNSCC refers to cancer that has returned after treatment, while metastatic HNSCC indicates that the cancer has spread to distant parts of the body, such as the lungs or bones. The disease progresses as cancer cells grow and invade nearby tissues, forming new tumors. This spread can occur through the lymphatic system or the bloodstream. As the disease advances, it can impair the function of the affected organs.