Thyroglobulin mRNA expression helps to distinguish anaplastic carcinoma from angiosarcoma of the thyroid

The existence of angiosarcoma (AS) of the thyroid has been a matter of deba te for many years, because some authors believe that most if not all ASs ar e in fact "angiomatoid" anaplastic carcinomas (ACs). Immunohistochemistry a lone was not successful in solving the problem, since cytokeratin expressio n is a known occurrence in AS. Therefore, we wanted to compare nine cases o f AS with ten cases of AC, assessing whether thy roglobulin (TG) mRNA was s till transcribed in undifferentiated tumors and could be helpful to disting uish AC from AS. The cases were analyzed for TG mRNA expression by means of radioactive in situ hybridization. The silver grains were counted using an automated device, and their amount was compared with that of stroma, backg round, and peritumoral thyroid. A weak signal was present in all AC but not in AS (mean counts 35.7 and 9.6 arbitrary units, respectively: P<0.01). In two cases of AC, residual areas of poorly differentiated insular carcinoma had a strong signal (similar to that of peritumoral thyroid). These findin gs further confirm that AC and AS of the thyroid are unrelated malignant tu mors.