Effect of topical tretinoin under occlusion on atypical naevi

Atypical naevi are potential precursors of melanoma and markers of increase d melanoma risk. To examine the possibility of chemoprevention of melanoma by retinoids, we studied the effect of topical tretinoin 0.1% (all-trans-re tinoic acid; vitamin A acid) and tretinoin 0.1% with hydrocortisone on atyp ical naevi. Thirty patients with atypical naevi were enrolled in a prospect ive randomized double blind study. For each patient three comparable naevi were selected and randomized to receive tretinoin 0.1% (T), tretinoin 0.1% with hydrocortisone 1% (C) or a placebo cream (P) once a week under Actider m occlusion for 4 months. Baseline views of the naevi, taken with a videomi croscope (magnification 20 x), were assessed for morphological changes comp ared with views taken 2 months after the beginning of treatment, 1 week aft er completion of treatment and 6 months later, After completion of the stud y all naevi in the T and C groups and six naevi in the P group were removed and evaluated histologically for the presence of atypia. The number of nae vi that had changed in colour or size was significantly higher in the T and C groups compared with the placebo group. A size reduction took place in 4 2.9% (T) and 40.0% (C) of the naevi and the colour changed in 75.0% (T) and 66.7% (C). The effect of treatment, in general subtle, did not differ sign ificantly between groups T and C, but naevi treated with C became significa ntly less irritated. Histologically, 75.0% of the naevi treated with T and 69.6% of the naevi treated with C were atypical, Therefore, no major change was seen in the clinical aspect of atypical naevi after treatment with tre tinoin 0.1% or tretinoin with hydrocortisone 1%, and most of the treated na evi still met the histological criteria for atypia after the treatment peri od. The current management of follow-up of atypical naevi and excision when change to melanoma is suspected is therefore still recommended. Neverthele ss, some response was seen, which may justify a further exploration of tret inoin and hydrocortisone 1% therapy for a longer treatment period in combin ation with research to clarify its mechanism. (C) 1998 Lippincott Williams & Wilkins.