Thyroid Transcription Factor 1 Immunohistochemistry as an Intraoperative Diagnostic Tool at Frozen Section for Distinction Between Primary and Secondary Lung Tumors

Context.—Intraoperative distinction between primary and metastatic carcinomas in the lung at frozen section remains problematic. Objective.—To assess the value and practicality of immunohistochemistry for thyroid transcription factor 1 at the time of intraoperative frozen section. Design.—Thirty-three patients presented with either a solitary pulmonary mass or 2 pulmonary masses and a history of carcinoma in a different organ. In addition to routine frozen section for assessment of tumor type, we looked for expression of thyroid transcription factor 1, using the EnVision system with abridged methodology. Results.—Ten cases were positive for thyroid transcription factor 1, which was confirmed on subsequent paraffin sections. Nine of these were confirmed as primary pulmonary adenocarcinomas, but 1 case proved to be a rare false-positive metastatic colonic carcinoma. Twenty-three cases were negative on frozen section and reported as favoring metastatic disease. In all cases, additional immunohistochemical data increased diagnostic confidence, but particularly in cases of positive primary pulmonary tumors and in cases with disease metastatic from sites other than the large bowel. The average time in addition to that of the basic frozen section was 24 minutes per test with a cost of £32 (US$57). Conclusions.—Frozen section immunohistochemistry for thyroid transcription factor 1 shows specificity and sensitivity similar to those seen for formalin-fixed tissues and is feasible within the time frame of a thoracotomy. Diagnostic confidence is increased, especially with positive primary pulmonary tumors. However, its practice should be properly planned within an operative procedure as liberal usage will likely have significant staff and cost implications.