Elsevier

Clinics in Dermatology

Volume 28, Issue 3, May–June 2010, Pages 249-253
Clinics in Dermatology

Actinic keratosis: Facts and controversies

https://doi.org/10.1016/j.clindermatol.2009.06.009Get rights and content

Abstract

Actinic keratoses are common lesions that are generally clinically diagnosed. Although currently most actinic keratoses are treated, whether this is truly necessary is debated. Treatment of all actinic keratoses is advocated because preliminary evidence indicates that actinic keratoses may progress to squamous cell carcinomas. Some also consider actinic keratoses equivalent to squamous cell carcinoma.

Introduction

Actinic keratoses (AKs), also known as solar keratoses, are common lesions that are seen in up to 40% to 50% of Australians aged older than 40 years.1 Early lesions may be more easily palpated, presenting as a rough spot.1 More developed lesions are scaly macules or papules, sometimes with an erythematous base.1 Lesions may be tender.2 Variables associated with AKs are age older than 80, male gender, excessive sun exposure, and fair skin type.3 The presence of AKs is associated with an increased risk of developing skin cancer.4, 5

Many different subtypes of AK have been identified (Table 1).6 In a typical AK, there is alternating orthokeratosis and parakeratosis. Orthokeratosis overlies adnexal ostia, and parakeratosis is seen above atypical keratinocytes that are budding from the base of the epidermis. This gives the stratum corneum a pink and blue alternating appearance.

The typical histopathologic features of AK are well accepted.2, 6, 7, 8 There is disagreement when atypia involves the full thickness of the epidermis yet spares adnexal epithelium. Some consider this pattern representative of a “bowenoid” AK, whereas others believe it is a manifestation of squamous cell carcinoma (SCC) in situ.6, 7, 8 Confounding this, the distinction between a thick AK and a thin SCC is somewhat subjective.9 Because of these difficulties, there is a proposed classification of AKs according to the degree of involvement of the epidermis by atypical keratinocytes (Table 2).10, 11, 12 This classification, analogous to the classification of cervical intraepithelial neoplasia and vulvar intraepithelial neoplasia, has not been widely adopted.10, 11

Section snippets

Is AK a neoplasm?

To answer this question, we must first define “neoplasm.” A neoplasm is a new growth in which the proliferative capacity and longevity of cells exceeds that of normal tissue.13 Neoplasms may be benign or malignant.13

Clonality provides evidence that one cell has expanded excessively, giving rise to an entire tumor. AKs have been shown to be clonal,14 with high rates of loss of heterozygosity, specifically on chromosome arms 17p, 17q, 9p, 9q, and 13q.15 Mutations in p53 have been documented on

Is AK benign or malignant?

The classification of a tumor as benign or malignant is not a simple task.13 The sine qua non of malignancy may be metastatic potential.13 For AKs defined by being histologically limited to the epidermis,6 there is no potential for metastasis beyond the epidermis. Nonetheless, some authors cogently argue that AKs are SCCs.10, 11, 20, 21, 22, 23 The histopathologic boundary between a thick AK and a thin SCC is subjective and arbitrary,9 and in this sense, AKs and SCCs are part of a continuum.24

Does an AK convert to squamous cell carcinoma?

This question presupposes that AKs and SCCs are not equivalent, and I will assume this is true. Epidemiologic, clinical, histologic, and genetic evidence exists for conversion of AKs to SCCs. Epidemiologically, similar patients are affected by AKs and SCCs.2 On a clinical basis, a lesion clinically diagnosed as an AK has been shown to change over time, with a subsequent histologic diagnosis of SCC.29 Furthermore, the microscopic contiguity of many SCCs with AK30, 31, 32 suggests that AKs are

Management of AKs

AKs are generally diagnosed clinically.41, 42 For the most part, different histologic subtypes of AK (Table 1) do not affect management, with the exception of hypertrophic AKs, which may be resistant to treatment.42 There is correlation between clinical features and degree of histopathologic epidermal involvement (Table 2), and the clinical presentation is most important in directing management.11 If the clinical diagnosis of AK is in question, a biopsy is warranted. In particular, it may be

Conclusions

AKs are very prevalent in sun-damaged skin, and it does patients a disservice to needlessly alarm them by equating AK with SCC.74 In the future, we may have a simple test that can predict which AKs will not regress, but until that time, most lesions should be treated with management tailored to individual patients and their lesions.41, 42, 49, 75 With increased study of AKs, we may end up with better answers.

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