Lasers, PDT May Have Niche inCancer Treatment

BALTIMORE — Lasers and light therapies have a limited role in the treatment of skin cancers and pigmented lesions, but their judicious use may be appropriate when standard treatments would be time consuming or provide poor cosmetic results, Dr. James Spencer said at a meeting sponsored by the Skin Disease Education Foundation.

Dr. Spencer, director of Mohs micrographic surgery at Mount Sinai Medical Center, New York, presented information to help physicians determine when it may be acceptable or unacceptable to use lasers or photodynamic therapies on skin lesions.

CO₂ Laser

Use of a CO₂ laser in continuous wave mode produces rapid and bloodless thermal destruction of tissue, but this mode has not been shown to be an effective treatment for skin cancer, he said. In a study of 24 basal cell carcinomas (BCCs) treated this way, 50% recurred after 1 year and healing after the procedure produced hypopigmentation and atrophy (J. Dermatol. Surg. Oncol. 1979;5:803–6).

Some studies have tested the theory that treatment of superficial skin cancers with the CO₂ laser in ultrapulsed mode could destroy the tumor and avoid scarring. In a series of 51 BCCs that were treated with the CO₂ laser in ultrapulsed mode, dermatologic surgeons were able to ablate 21 superficial BCCs reliably if the level of ablation penetrated to the midreticular dermis or deeper. Attempts to use this method with 28 nodular and 2 infiltrating BCCs were not successful (Br. J. Plast. Surg. 2000;53:286–93).

In another study, two or three passes of an ultrapulsed CO₂ laser on 17 superficial BCCs and 13 squamous cell carcinomas (SCCs) in situ with 3-mm margins onto normal skin left an unacceptably high rate of lesions positive for cancer when they were excised and examined in serial sections. For superficial BCCs, two passes left five of eight lesions positive and three passes left zero of nine lesions positive. Treatment of in situ SCC with two passes yielded two of six lesions positive while three passes resulted in three of seven lesions being positive (Arch. Dermatol. 1998;134:1247–52).

Dr. Spencer said that he did not think CO₂ lasers should realistically be a part of a dermatologist's armamentarium against skin cancer, but he suggested that the CO₂ laser may be considered to treat actinic cheilitis and basal cell nevus syndrome, "where your role is not cure, but control, and you're trying to avoid too much mutilating surgery."

Intravenous and Topical PDT

Intravenously administered photodynamic therapy (PDT) with agents such as porfimer sodium (Photofrin) is being studied for a variety of cancers, but its side effect of photosensitivity for 4–6 weeks through the skin and eyes creates a problem in using it for skin cancers. "If you're dying of a stomach cancer, you will hide in a dark room for a month, but if you've got some basal cell skin cancers, I don't think you will," Dr. Spencer said.

In a prospective study, PDT with intravenous Photofrin and red light yielded a complete response rate of 88% after an average follow-up of 29 months in 37 patients who had a total of 151 BCCs (most patients had basal cell nevus syndrome). Tumors recurred, however, in 36% of lesions on the nose and in 89% of morpheaform tumors (Arch. Dermatol. 1992;128:1597–601).

PDT researchers are studying shorter-acting light-sensitizing compounds that preferentially accumulate in malignant cells to avoid the problem of persistent photosensitivity with Photofrin. Verteporfin, an intravenously administered agent approved for ophthalmologic use that photosensitizes patients for only a few days, is undergoing clinical trials to test its efficacy in skin cancer, he said.

Topical PDT agents such as delta-aminolevulinic acid (ALA), which avoid the photosensitizing problem altogether, have had reported recurrence rates of 44% in 95 superficial BCCs and 69% in 35 superficial SCCs after 19 months of follow-up (Arch. Dermatol. 1998;134:821–6). "You should not be doing this in your practice," said Dr. Spencer, who also has a private practice in St. Petersburg, Fla.

Eyelid tumors may represent the best opportunity to try topical ALA because it is usually desirable to avoid surgery in that area and ALA may be able to more fully penetrate the thin skin of the eyelid, he suggested. In one study, topical PDT ALA treatment clinically resolved 8 of 19 nodular BCCs on the eyelids and periocular skin, while the other lesions had partial or no response (Acta Ophthalmol. Scand. 1999;77:182–8).

In a study of topical PDT with methyl-5 ALA, 79% of 350 nodular BCCs that were curetted before treatment with PDT were clinically clear. After 2–4 years' follow-up, 11% of the clinically clear lesions recurred (Br. J. Dermatol. 2001;145:467–71).