Failure of leucovorin rescue to prevent reactivation of a solar burn after high dose methotrexate.

A 21-year-old patient with metastatic osteosarcoma was receiving methotrexate with leucovorin rescue every 2 weeks. After the second (of four) infusions of methotrexate, a prior solar burn on an area of skin was reactivated in spite of leucovorin rescue. An area of skin treated 5 months previously by radiation was spared the effects of the reactivation phenomenon. No other toxicities appeared. The reactivation of the solar burn is an example of "false photosensitization" and this cutaneous toxicity is not ameliorated by leucovorin. Methotrexate therapy should be delayed until the effects of generalized solar burns have resolved (approximately 1 week).