Expression of human tumor-associated antigen RCAS1 in adult T-cell leukemia/lymphoma

In human cancer, RCAS1 (the receptor-binding cancer antigen expressed on SiSo cells) on the surface of various kinds of tumor cells reportedly induces the apoptosis of T-cells and natural killer cells, resulting in evasion of the immune system. In the present study, an immunohistochemical analysis of RCAS1 expression was performed with lymph node specimens obtained from patients with adult T-cell leukemia/lymphoma (ATLL), Positive staining was seen in 15 (75%) of 20 cases and in all cases of patients with short survival times. In the cases of B-cell lymphomas, positive staining was seen in only 1 (13%) of 8 cases. These findings indicate that expression of RCAS1 may be associated with the evasion from immune surveillance of cells infected with human T-lymphotropic virus type I, resulting in the development of overt leukemia/lymphoma. Determination of RCAS1 expression may be useful for predicting the prognosis of patients with ATLL.