Some authors [25] stated that immunohistochemical studies, similar to morphology, have marked overlap in the staining characteristics between pseudosarcomatous myofibroblastic proliferations, sarcomatoid carcinoma, and leiomyosarcomas, even though they had recently observed that the use of a judicious panel of immunostaining agents (pan-cytokeratin, smooth muscle actin, desmin, Alk-1, p63, CK5/6, and/or high-molecular-weight cytokeratin) interpreted strictly within the morphological context may be of some value. The gene discussed is KRT5; the disease is sarcomatoid carcinoma.