[Adenocarcinoma and basaloid squamous cell carcinoma in the same lung lobe]

We encountered a rare case of an adenocarcinoma and basaloid squamous cell carcinoma in the same lung lobe. The patient was a 66-year-old female. During the observation of the course of angina pectoris, chest computed tomography( CT) showed a nodular shadow in the right upper lung field and a club like lesion dorsal to this shadow. Since the former lesion was diagnosed as an adenocarcinoma, right upper lobectomy and lymph node dissection were performed. The latter lesion was diagnosed as a basaloid squamous cell carcinoma by pathology. Basaloid squamous cell carcinoma is a relatively rare tumor associated with a poor prognosis that is classified as a subtype of squamous cell carcinoma. There have been no reported cases of this tumor developing concurrently with adenocarcinoma. Since there were no histological transition images, and immunostaining findings completely differed between the 2 tumors, these tumors may have incidentally developed during the same period in the same lung lobe.