β2-microglobulin (β2m) is a small polypeptide, related to the immunoglobulins and present on nucleated cells as part of the strong transplantation antigens. Elevated plasma levels have been recorded in patients with various malignant diseases. Human β2m has also been detected immunohistochemically in carcinomas transplanted into nude mice, and in the plasma of tumour-bearing mice. In the present study the occurrence of human β2m was studied in the plasma of 26 patients with squamous cell carcinoma (SCC) of the head and neck and in six heterotransplanted carcinoma lines. Extractable β2m was measured in seven SCC of the head and neck and in the six heterotransplanted tumour lines. Immunohistochemically detectable β2m was studied in 20 SCC and in six heterotransplanted tumour lines. Only 3 of 26 patients (12% had elevated p-β2m levels. Stage IV tumours seemed to have more p-β2m (though within the normal range) than did less advanced tumours. There was no correlation between the total amount of extractable β2m in the patients' tumours and p-β2m. However, there was an association between the concentration of β2m in the tumours and p-β2m. Human β2m could be detected in the plasma of mice with tumours from all tumour lines, and there was a tendency toward an association between tumour size and p-β2m. The ratio of p-β2m/tumour volume differed between the tumour lines. Tumour volume doubling time (DT) was determined for the various tumour lines, and there was a correlation between DT and β2m concentration of the tumours. The mean β2m concentration was ten times as high in patients' tumours as in heterotransplanted tumours, which indicates a faster growth of heterotransplanted tumours than of tumours in man. Membrane-bound β2m was immunohistochemically detectable both in SCC of the head and neck and in heterotransplanted tumours. The implications of the findings of the present study for the use of β2m as a tumour marker and the importance of the association between concentration of extractable tumour β2m and DT are discussed.
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