In summary, Hiroshima et al. [101] have reported HEG1 staining in most PEMs and in the epithelioid component of PBMs with a membranous, strong, and diffuse pattern of expression and, at the same time, the substantial lack of expression in lung carcinomas, except for rare cases of focal staining in squamous cell carcinomas or squamous components of lung adenosquamous carcinoma. The gene discussed is HEG1; the disease is lung carcinoma.