Anaplastic small cell neoplasms of the thyroid: an immunoperoxidase study.

The cell origins of ten anaplastic small cell neoplasms of the thyroid gland were investigated using the immunoperoxidase technique. Sections of the neoplasms were examined for immunostaining for the tissue markers of B lymphocytes, thyroid follicular cells, and C cells by incubation with antisera to the lambda and kappa light chains, human thyroxine and human calcitonin, respectively. Six neoplasms were identified as malignant lymphomas, and two were identified as anaplastic small cell follicular carcinomas. The cell origins of the remaining two neoplasms could not be determined. The prognosis for patients with malignant lymphoma was favorable compared with the prognoses for patients in the other two groups. The prognosis for patients with anaplastic small cell follicular carcinomas was better than for those with small cell malignancies of undetermined cell origins. These findings suggest an important role for the immunoperoxidase technique in the precise classification of anaplastic small cell neoplasms of the thyroid.