The carcinogenic properties of topical PUVA. A lifelong study in mice

The tumorigenic properties of topical methoxsalen (8-MOP) and trioxsalen (TMP) plus ultraviolet light A (UVA) were studied in NMRI female mice. The animals were treated three times weekly for 9 months, and followed up for 18 months. Acetonic solutions of TMP (0.1 mg in 0.2 ml) and 8-MOP (0.6 mg in 0.2 ml) were applied to the shaved back skin of the mice and irradiated with UVA. The doses needed to elicit equivalent phototoxic effects were 0.29 J/cm2 in the TMP group and 1.09 J/cm2 in the 8-MOP group. Papillomas, keratoacanthomas, and squamous cell carcinomas developed in the 8-MOP group only, and the first tumor was seen at 10 months after the beginning of the study. The results suggest that the carcinogenicity of these two modes of photochemotherapy may differ.