according to their lesion pattern (scattered isolated lesions, lesions clustered in small areas, or large affected fields), without reference to the absolute numbers of lesions.7
Clinical Classifications for AK lesions: What They Give Us
Although several classification systems have been suggested for AK over the years, currently there is no gold standard in clinical practice to guide the therapeutic approach.8,9
Lesion-based assessment: Olsen – clinical classification of AK
The original Olsen classification emerged 30 years ago (1991) in the context of a clinical trial. The intention of Olsen et al was not to establish a clinical classification of AK per se, but to assess the efficacy and safety of masoprocol in the treatment of AK.10 They created a global AK lesion scale of 1 to 3, based on the overall thickness of AK, and a 7-grade scale to assess the overall response to treatment.
In this regard, the classification presented shortcomings and limitations because it was based on imprecise terminology that was not intended for the objective classification of lesions.10 Over the years, Olsen grades have been modified, describing AK lesions according to their thickness and degree of hyperkeratosis on clinical examination. Interestingly, however, in the first original publication of the Olsen group (1991) the term 'hyperkeratosis' was not even mentioned among the initial lesion criteria.10 Although some guidelines base their treatment decisions for AK on this classification,11,12 many others do not (ie, Spain,13 Switzerland,14 and Germany,15 among others).
Given that clinicians want to prevent patients from developing AKs into invasive squamous cell carcinoma (iSCCs), a classification that determines the risk of AK lesions or the field progress is needed. However, the Olsen classification carries no predictive value. For this reason, and other key issues mentioned below, this classification should be dismissed.
First, the distinction between the absence or presence of hyperkeratosis in terms of palpation and visualization is unreliable and not standardized, as dermatologists do not consistently evaluate lesions.18 This makes Olsen a rather imprecise, subjective classification, especially when distinguishing between stage I or II lesions (see Figure 1). Second, a three-dimensional scale is misleading, as it implies a fixed progressive escalation. Olsen intends a continuum of “increasingly dangerous†grade I to III lesions, while no correlation has been found between Olsen grade and rate of progression. Third, Olsen addresses only single lesions, although these are only a component of FC. In this respect, and as a fourth argument, interobserver agreement of Olsen grading and individual lesion counts are neither good nor consistent.19-21 Finally, Olsen grades do not correlate with underlying histology (ie, Röwert-Huber classification).22,23 Comparatively, both systems do not match accurately (54% of agreement);23 and more than one-third of lesions clinically classified as Olsen grade III appear histologically as AK I. Both Olsen and Röwert-Huber classifications have shown limited use for clinical practice.1,24,25 In fact, the risk of transformation of an individual AK lesion to iSCC cannot be predicted based on clinical or histological features.26
Field-based assessments: AKASI and AK-FAS
Until recently (2017) the severity of AK has been mainly evaluated by subjective assessment of patients. Thereafter, there have been attempts to globally view and objectify the classification of AK lesions.
