Xeroderma pigmentosum and squamous cell carcinoma of the tongue. Identification of two black patients as members of complementation group C.

We present the identification and characterization of two patients with xeroderma pigmentosum (XP) and squamous cell carcinoma of the tongue. Dermal fibroblasts from two black siblings with XP were shown to be hypersensitive to ultraviolet (UV) light measured by colony-forming ability. UV-induced unscheduled deoxyribonucleic acid synthesis was reduced significantly when compared with normal levels for both strains. The strains were assigned to complementation group C on the basis of cell fusion studies. Patients with XP have a marked increase over normal persons for developing skin cancer, presumably because of their extreme sensitivity to UV light. Our results may have applicability in explaining the in vivo development of epidermoid carcinoma in the partially shielded tongue of some XP patients.