[Aberrant TTF1 expression in anaplastic large cell lymphoma]

Thyroid transcription factor 1 (TTF1) is the most common and reliable marker for immunohistochemical diagnostics of various thyroid tumors and lung adenocarcinoma. At the same time, some of scientific studies have been published that describe aberrant expression of TTF1 by cells of various tumors, including lymphomas. Researchers reported the possibility of TTF1 expression in diffuse large B-cell lymphoma, angioimmunoblastic T-cell lymphoma, and T-cell leukemia. However, there were no reports of this marker expression in anaplastic large cell lymphoma, which, due to its morphological characteristics, may resemble a metastatic process.

To assess the frequency of aberrant expression of TTF1 in anaplastic large cell lymphoma cells.

The study was performed on 47 cases of anaplastic large cell lymphoma. The expression of TTF1 was assessed using two different platforms (Ventana BenchMark ULTRA and BondMAX) and two different, commercially available, clones (SP141, SPT24), including the use of a double chromogenic label.

The study detected the expression of TTF1 by tumor cells in five cases (10.6%) of nodal ALK-negative anaplastic large cell lymphoma in patients with a median age of 66 years, with a TTF1 expression gradient from 100% to 15% of tumor cells.

The study demonstrated for the first time the possibility of aberrant expression of TTF1 by anaplastic large cell lymphoma cells. In one case, intense expression of TTF1 was observed in 100% of tumor cells, in the rest - in no more than 15%. Moreover, expression was observed both in cases of using clone SP141 and clone SPT24. In our opinion, the identified aberrant expression of TTF1 in anaplastic large cell lymphoma, may cause an error in the morphological diagnosis of the metastatic process and requires additional attention from the pathologist.