Tumors as a Paradigm for the In Vivo Role of Chemokines in Leukocyte Recruitment

Ever since the first description by Virchow in 1863, histopathologists have recognized the occurrence of host leukocytes in tumor tissues and/or at their periphery. Interestingly, Virchow felt that the frequent presence of a lymphoreticular infiltrate in human neoplasms reflected the origin of cancer at sites of previous chronic inflammation. In 1907 Hardley reported that normal cell infiltration in malignant melanoma indicated a “regressive process.” This observation marked a complete change in the general opinion as to the significance of the “lymphoreticular infiltrate,” a change reflected by a number of reports on pathology and prognosis. These opposite ways of looking at the relationship between leukocyte infiltration and malignancy have polarized views in the field but, indeed, reflect the pleiotropic, ambivalent functions of infiltrating cells.