Cancer remains a leading cause of mortality globally, and its yearly death toll of 8.2 million people is only anticipated to rise as the world's population ages. The presence of tumor-associated inflammatory cells in cancers poses a critical concern that is one of oncology's most pressing issues. Immunotherapy, which targets the immune system, has revolutionized cancer treatment in the previous decade. Many important questions about the causal relationship between chronic inflammation and carcinogenesis have been answered by immunological tests over the last two decades. Recent clinical and preclinical research has begun to reveal the wide range of systemic immune perturbations that occur during cancer development, and the critical role of peripheral immune cells in the anticancer immune response.