Basal cell carcinoma with squamous differentiation could mean several things and this has been the subject of some debate. It could mean separate tumors, one basal cell carcinoma and the other, squamous lying so close that the elements of each collide. This is called a collision tumor. The alternative is that it is a baso-squamous carcinoma, a separate entity that has elements of both basal and squamous cell carcinomas, but has potential of being more aggressive than either. Basal cell carcinoma rarely metastasizes (goes to internal organs). I've had seven such patients over my career. Squamous cell carcinoma, on the other hand, metastasizes in approximately 0.9% patients. Baso-squamous carcinoma has a 10% metastatic rate. In all cases, if there is metastasis, the lung is usually the target. This rate is high enough to warrant a chest x-ray be done to determine if there is lung involvement. While baso-squamous carcinoma is relatively rare, I've had 2 patients with this diagnosis this year. Happily, chest x-rays of both revealed no sign of lung involvement.
