TTF1 and medical procedure: In a study on the correlation between TTF‐1 and the production of mucus in the lungs, Yutaka et al.,16 through mice experiments, found that positive TTF‐1 was expressed in non‐mucinous adenocarcinoma of the lung, whereas negative or weakly positive TTF‐1 was expressed in mucinous adenocarcinoma of the lung.17