Eosinophils and human cancer

Eosinophils are rare granulocytes that are normally associated with allergic diseases or responses to various parasitic infections. Many types of human cancer, however, are also associated with extensive eosinophilia, either within the tumor itself, or in the peripheral blood, or in both locations. Special techniques such as autofluorescence or immunohistochemistry are sometimes needed to detect the presence of intact and degranulating eosinophils within the tumors. With the help of these techniques, extensive eosinophilia is most often seen in hematologic tumors such as Hodgkin's disease and certain lymphomas; however, many other types of cancer such as colon, cervix, lung, breast, and ovary also contain eosinophilia if diligently sought. Although the presence or absence of eosinophilia within these tumors does not appear to have a major influence on the prognosis of the patient, eosinophils may play an important role in the host interaction with the tumor, perhaps by promoting angiogenesis and connective tissue formation adjacent to the cancer. In addition, tumor-related eosinophilia provides some interesting clues into tumor biology, particularly with regard to production of cytokines by the tumor cells.