Although precancerous,24,25 the probability of a given AK undergoing malignant transformation is unknown.13 Reported risk of progression to SCC for individual lesions ranges from 0-025 to 16% per year.26 The 10-year risk of malignant transformation of at least one AK on a given patient is 10-2%.27 The relative risk of malignant transformation depends ultimately on factors related to the AK itself (for example, thickness), as well as patient characteristics (for example, drug therapy, degree of pigmentation, immune status).5 However, another aspect that may confound estimation of the prognosis of AK is in the spontaneous regression rate. A recent study from Queensland28 reported a spontaneous regression rate of 85% (95% CI: 75-96%) in subjects with prevalent AK (AK diagnosed on a person during their first examimation) and 84% (95% CI: 72-96%) in persons with incident AK (AK appearing for the first time during the study). However, the distribution of lesions per person was highly skewed, with 12% of subjects having 65% of the total number of AK.

BD is associated with an excellent prognosis, related to the disease's indolent nature and its favourable response to a range of therapy. Retrospective studies demonstrate an approximate 3% progression rate to SCC,29,30

which is further associated with an approximate 33% metastasis rate.31 Contrary to findings of earlier reports.32-35 a meta-analysis of 12 studies in 1989 determined no significant association between BD and internal malignancy.36

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