MHC-class I antigen expression on micrometastases in bone marrow of patients with head and neck squamous cell cancer

Although squamous cell carcinoma of the head and neck region very rarely metastasize to the skeleton, epithelial cells have been found in bone marrow aspirates of these patients. This observation reflects the general spread of the disease, indicating a poor clinical prognosis with a much higher risk of developing local or distant recurrences. In a first attempt to characterize the phenotypic properties, the expression of the major histo-compatibility complex (MHC) class I antigens on bone marrow micrometastases was assessed. It has been shown that the down-regulation of these molecules is a potential mechanism to escape from HLA class I restricted lysis by cytotoxic T-cells. The significance of reduced MHC class I expression might be relevant for the survival of residual metastatic cells in the bone marrow of patients with squamous cell carcinoma of the head and neck region. Bone marrow aspirates were screened for individual disseminated epithelial cells using the immunoalkaline phosphatase technique with monoclonal antibodies to the epithelial differentiation marker cytokeratin 19 (CK19), as described previously. Specimens containing CK19-positive cells were colabelled with the monoclonal antibody W6/32. The loss of MHC expression is not related to the tumor stage but clearly to the degree of differentiation: 6 out of 7 patients with low-grade SCCHN, but only 3 out of 13 patients with medium-grade SCCHN showed a complete loss of MHC class I molecules. This finding could indicate the reduced prognosis of undifferentiated SCCHN. The lack of MHC class I expression could encourage the survival of residual tumor cells in the bone marrow of patients with SCCHN that evade immunosurveillance.