The immune system, interacting intimately with the cancer cells in a tumor, may combat or favor cancer development and progression, or both. One of the most important risk factors for solid cancers is age. With increasing age, numerous alterations at multiple levels including molecular, cellular, organ, and systemic are occurring. With age many physiological systems are changing, including the immune system. Several alterations occur in both arms of the immune system with aging. Although the innate immune system shows changes with aging, the most important alterations occur in the adaptive immune system, especially involving T cells. Many changes in the immune system may decrease its capacity to combat the emerging or progressing tumor. Further, the age-related immune changes may favor the cancer development. The most important changes which may decrease the immune response efficiency are the changes in T cell functions and phenotypes, concomitant with the presence of a low-grade inflammation. A consensus is now emerging in oncology that not only the cancer cells themselves should be studied but also their macro-and microenvironments. In this context, the study of the interrelation of the immune response and the tumor at various stages is essential to enhance our capacity for intervention in elderly cancer patients.