TTF-1 expression in breast carcinoma: an unusual but real phenomenon

To evaluate thyroid transcription factor-1 (TTF-1) expression in a large cohort of invasive breast carcinomas (IBCs) using two commercially available monoclonal antibody clones (8G7G3/1 and SPT24).

Nuclear and cytoplasmic TTF-1 expression was evaluated in 1132 primary IBCs and 208 primary pulmonary carcinomas using tissue microarray (TMA) sections. TTF-1 nuclear expression was detected in one of 1132 (0.09%) IBCs by 8G7G3/1. In pulmonary carcinoma, TTF-1 expression was detected in 149 (71.6%) and 147 (70.6%) cases by 8G7G3/1 and SPT24, respectively, with no significant difference being seen between the two clones (P = 0.839), and there was good consistency between these two antibodies in differentiating breast and pulmonary carcinomas (kappa value 0.905; P < 0.001). Both clones showed high specificity but relatively low sensitivity. Cytoplasmic TTF-1 expression was detected in 44 IBCs by 8G7G3/1, and this particular expression pattern was an independent adverse prognostic factor.

Both TTF-1 antibodies (clones 8G7G3/1 and SPT24) were useful in differentiating breast from pulmonary carcinomas. Nuclear expression of TTF-1 was detected in IBCs by 8G7G3/1, but not by SPT24. Cytoplasmic expression of 8G7G3/1 was seen in IBC for the first time, and was an independent unfavourable prognostic factor.