A new concept of basal cell epitheliomas based on the three-dimensional growth pattern of the superficial multicentric type.

Little is known about the growth characteristics of basal cell epitheliomas (BCEs), largely because of the difficulty in studying these tumors, both in situ and in vitro. In this study, the authors report that a scanning electron microscopic examination of 2 cases of superficial BCEs reveals that the tumor proliferates centrifugally as a monolayer beneath the epidermis as well as over the surfaces of hair follicles, while eroding and replacing the original basal architecture. Behind the leading edge of this monolayer, the cells split away from the epidermis to form a round border resembling a carpet being rolled up. This border then develops into a mass lesion, which represents the tumor cell foci seen in routine paraffin sections. These findings have led the authors to propose a fundamentally different explanation for the pathogenesis of these tumors: BCEs are conditioned neoplasms that require contact with the epidermal or hair follicular epithelium in order to grow. This hypothesis could explain the behavior of BCEs as well as the clinical and pathologic varieties observed in clinical practice.