Affiliations: [a]
Division of Medical Oncology, Department of Internal Medicine, Sault Area Hospital, Sault Ste Marie, ON, Canada
| [b]
Department of Pathology, Sault Area Hospital, Sault Ste Marie, ON, Canada
| [c]
Division of Clinical Sciences, Northern Ontario School of Medicine, Sudbury, ON, Canada
Correspondence:
[*]
Corresponding author: Ioannis A. Voutsadakis, Division of Medical Oncology, Sault Area Hospital, 750 Great Northern Road, Sault Ste Marie, ON P6B 0A8, Canada. E-mail: [email protected], [email protected]
Abstract: Thyroid Transcription Factor 1 (TTF-1) is often used for the immunohistochemical evaluation of lung cancers, as a significant proportion of these cancers are positive while other adenocarcinomas are usually negative. Breast cancers are known to express TTF-1 only in a small minority of cases but this may be problematic when this staining is used for its differential diagnosis from lung cancer. We present a case of ER-positive breast cancer in 30% of tumor cells that was also TTF-1 positive in some areas of the primary tumor but lost ER expression completely in the metastatic recurrence site while retaining TTF-1 positivity. Additionally, a PTEN mutation was present on genomic evaluation of the primary tumor. Diagnostic, pathogenic and therapeutic implications of these findings are discussed.
Keywords: Breast cancer, TTF-1, Estrogen Receptor, diagnosis, PTEN mutation
