Medullary (C cell) carcinoma of the thyroid with features of follicular oxyphilic cell tumours.

During the last few years the spectrum of histological features seen in tumours of C cell origin has broadened and, among other variants, papillary and glandular forms have been recognized. Seven cases are now reported of medullary carcinoma with features of oxyphilic follicular cell tumours. These cases were studied with routine techniques and an immunolocalization method using antibodies to calcitonin and thyroglobulin. The tumours were mainly composed of well-demarcated eosinophilic cells of variable size arranged in trabecular, solid and follicular structures. One of the cases was negative for calcitonin but displayed strong diffuse argyrophilia and amyloid deposits; two amyloid-free tumours revealed argyrophil granules and were positive for calcitonin, the immunoreaction being inconspicuous in one however. Apart from trapped normal thyroid follicles, thyroglobulin was absent in the tumours. It is concluded that medullary carcinoma should be considered in the differential diagnosis of thyroid oxyphilic cell tumours, even when showing glandular differentiation, and that immunolocalization techniques using calcitonin and thyroglobulin in combination with methods for demonstration of argyrophil granules and amyloid are essential for accurate diagnosis of this type of medullary carcinoma of the thyroid.