Spindle cell tumor with histiocytic and myogenic marker expression in the lymph node of a human T-cell leukemia virus type 1 carrier.

Carriers of oncogenic human T-cell leukemia virus type 1 (HTLV-1) can develop adult T-cell leukemia/lymphoma (ATLL). While an increasing number of animal models of HTLV-1 infection have revealed that malignant tumors with a histiocytic phenotype can arise, they have not been reported in humans. Here, we present a 79-year-old female HTLV-1 carrier who presented with a swollen lymph node. Histological examination revealed that the lymph node was replaced with a malignant spindle cell tumor, but not ATLL. Immunohistochemical analysis indicated that the tumor was positive for histiocytic (CD68 and CD163) and myogenic (α-smooth muscle actin, desmin, and caldesmon) markers, suggesting some differential diagnoses. We could not reach a definitive diagnosis under the current notion of the disease entity. In addition, we could not provide an exact causal relationship between HTLV-1 infection and the development of the current tumor. Nevertheless, this tumor may be a human counterpart of murine HTLV-1-related histiocytic tumors. Curiously, the tumor showed a good response to chemotherapy with the combination of cyclophosphamide, vincristine, and prednisone, a standard approach for ATLL. This case might represent a novel entity of an HTLV-1-related malignant tumor. Further accumulation of case reports will certainly contribute to our understanding of human HTLV-1-related disease and the mechanism of viral oncogenesis.