Kinetics of cell proliferation in benigh and premalignant tumors of the human epidermis.

A double labeling method with two levels of tritiated thymidine was used to study 6 patients with seborrheic keratosis, 1 with a fibroepithelial tumor of Pinkus, and 1 with basal cell nevus syndrome manifesting three pits on the palm of the hand. The two latter types of lesions, known to be able to evolve into basal cell carcinoma, had an increased S-phase duration (18 hr for the germ cells of the palmar pits) as compared with normal epidermis (10 hr). This situation was similar to that observed in basal cell carcinoma, However, the S phase was not lengthened in seborrheic keratosis (9.2 plus or minus 1.6), a benign tumor in which malignant transformation is extremely rare. S phase was also of normal duration in the benign eosinophilic septa of the tumor of Pinkus.