Case Report TTF1 Expression in Pulmonary Metastatic Rectal Adenocarcinoma Sara Aversa and Cristiana Bellan Department of Medical Biotechnologies, Section of Pathology, University of Siena, 53100 Siena, Italy Correspondence should be addressed to Cristiana Bellan; cristiana.bellan@unisi.it Received 12 August 2018; Accepted 25 November 2018; Published 5 December 2018 Academic Editor: Chia-Tung Shun Copyright © 2018 Sara Aversa and Cristiana Bellan. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tyroid transcription factor (TTF-1) is a tissue-specifc nuclear transcription factor expressed developing thyroid, respiratory epithelium, and diencephalon. TTF-1 is thought to be expressed specifcally in most thyroid tumors and in a signifcant subset of pulmonary neoplasms. However, recent studies on its expression in extrapulmonary carcinomas have demonstrated that TTF-1 is not as specifc for lung and thyroid carcinomas as was previously thought: positivity of this marker can be observed, although much less frequently, in some carcinomas arising in other organs, such as the ovaries, endometrium, colon, and breast, as well as in some tumors of the central nervous system. Case reports of patients with TTF-1-positive colon adenocarcinoma are present in medical literature, but there are only a few cases of TTF-1-positive rectal adenocarcinoma. We present the case of a patient with rectal adenocarcinoma with lung metastasis found to be TTF-1-positive on immunohistochemistry. A review of the available literature is also included. 1. Introduction Te thyroid transcription factor (TTF-1) is a nuclear protein, part of the Nkx2 gene family. Its expression in normal tissues is restricted to the thyroid and pulmonary epithelium [1, 2]. In lung adenocarcinoma, TTF-1 has been considered a highly sensitive (up to 84% sensitivity) and specifc marker (85–100% specifcity) for primary lung adenocarcinoma, and it is therefore used as a reliable tool in distinguishing primary lung adenocarcinoma from other malignancies [3]. Nevertheless, in recent years, several studies have highlighted that some cancer arising in other organs, in particular in the intestinal tract, can manifest positivity for this marker [1, 2, 4]. Rare cases of patients with TTF-1-positive rectal adenocarcinoma have been reported. Here, we present a case of rectal cancer with TTF-1-positive lung metastasis which highlights the importance of using additional panels. 2. Case Presentation A 69-year-old patient was diagnosed with a rectal ade- nocarcinoma (G2) on biopsy afer an endoscopic control examination in 2013. He was treated frst with radio adjuvant chemotherapy and subsequently with surgery. Tis combi- nation of treatments has led to a complete response: any residual areas of cancer and lymph node involvement were documented on the surgical piece (yPT1N0 A/I G2 Sec MANDARD). In 2018, during regular oncological follow-up, a subpleural pulmonary nodule in lower lobe of the lef lung of about 15x10 mm was detected. Considering the patient's clinical history, his general conditions, and localization of the lesion, a surgical resection of the lung was performed. On the macroscopic exam of the sample, physicians observed a neoformation of 1.9x1.5x0.6 cm, which is whitish, solid, with irregular but well-defned margins, 0.6 cm away from the surgical suture and 0.1 cm from the visceral pleura. Histologic examination demonstrated an epitheliomorphic neoplasm with acinar diferentiation (Figure 1). Te adenocarcinoma cells were positive for cytokeratin 20 (CK20) and scattered positivity for caudal type homeobox 2 (CDX2) was found. TTF-1 was also strongly and difusely positive. Te tumor cells were negative for CK7 and Napsin A. Retrospective review of his previous primary tumor tissue showed similar histologic fndings with TTF-1 positivity. On the basis of the Hindawi Case Reports in Gastrointestinal Medicine Volume 2018, Article ID 6405125, 3 pages https://doi.org/10.1155/2018/6405125