A guarded green light for photodynamic therapy

Excision's more effective on nonmelanoma skin cancers,
yet PDT gets the nod for facework

By Owen Dyer

Photodynamic therapy (PDT) is the newest treatment for nonmelanoma skin cancers, tumours that have traditionally been treated by excision, curettage and electrodesiccation, cryosurgery, or occasionally x-ray therapy.

Nobody expected photodynamic therapy to achieve better outcomes than existing treatments in terms of curing the disease -- existing methods are highly effective at that -- but the technique holds promise for lesions in cosmetically sensitive areas like the face, because of the absence of scarring.

The question mark hanging over the new treatment has been whether the advantages of the therapy will carry too high a price in terms of disease recurrence. Two studies in the January issue of the Archives of Dermatology examined that question.

PDT works in combination with a photosensitizer that may be applied topically or taken systemically. A Europe-wide study involving 101 patients tested photodynamic therapy in combination with the topical photosensitizer methyl aminolevulinate (MAL), measured against excision in patients with previously untreated nodular basal cell carcinoma (BCC). Fifty-two patients received PDT with MAL, and 42 underwent excision. Most of these patients had one lesion, less than 15mm in diameter, located on the face and scalp or the trunk and neck.

DOUBLE TROUBLE?
The majority of patients in the MAL/PDT group were treated with one cycle made up of two sessions seven days apart. A 1mm thick layer of MAL cream was applied to each lesion and covered with an adhesive dressing, followed three hours later by rinsing and exposure to red light (570-670nm) at a dose of 75J/cm². Thirteen patients were judged at three months to require a second cycle.

Photodynamic therapy did not achieve clinical results as reliable as excision. At three months, 91% of the MAL/PDT patients were tumour-free, compared to 98% of excised controls. At one year, the figures were 83% and 96% respectively. At the 24-month mark, there were five new lesions in the PDT group compared to just one in the excision group.

If BCC were as dangerous as melanoma, these results would sign the death warrant of PDT. In fact, since the new lesions can be treated again, and dermatologists are almost as concerned about cosmesis as recurrence, the therapy is still alive. PDT outscored excision by a wide margin both in self-assessment and physician assessment of cosmetic results at all stages. At 24 months, 97% of PDT patients reported good or excellent cosmetic results, compared to 75% of surgical patients. At the same point, the clinicians gave good marks to 83% of the PDT patients' results, compared to 41% of the surgical patients.

The second PDT trial, involving a systemic photosensitizer, took place in both Canada and the US. Fifty-four patients received systemic verteporfin by injection followed one to three hours later by PDT. Tumours were exposed to either 60, 120, or 180J/cm² of red light (688 +/- 10nm) from a light-emitting diode panel.

Response rates climbed significantly with increasing dosages. At two years after treatment, the rate of complete clinical response was 95% in the 180J/cm² group but only 51% in the 60J/cm² group. There was a cosmetic trade-off at the higher dosages, but the difference tended to fade over time.

In an accompanying editorial, Dr Colin Morton of the Falkirk Royal Infirmary in Scotland comments: "It remains unclear whether verteporfin represents a significant superiority of effect over topical PDT with comparisons of efficacy, cosmesis, and protocol convenience required. It is possible that verteporfin PDT may be advantageous for thick nodular BCC and recurrent BCC, where maximising depth of light and photosensitiser preparation are of particular importance."