An aging population that is living longer in an atmosphere with a declining ozone layer, coupled with more outdoor and leisure time to bask in the sun, has led to a dramatic increase in sun-related skin damage (dermatoheliosis), skin cancers, as well as precursors to skin cancer such as actinic keratoses.

Actinic keratosis (AK), also known as solar keratosis, is the most common sun-related skin growth. Whether this lesion is benign (premalignant) or malignant (squamous cell carcinoma in situ) from its onset is a controversial issue. What is accepted, however, is that AKs have the potential to develop into invasive squamous cell carcinomas.

The development of AKs, is directly related to cumulative sun exposure, and is estimated that 60% of predisposed people older than 40 have at least one AK.

AKs are most common in persons who are fair-skinned, burn easily, and tan poorly particularly those who work, or have worked, in outdoor occupations, such as farmers, sailors, and gardeners, and those who participate in outdoor sports.

The incidence of AKs, as with all of the skin cancers described in this chapter, is highest in Australia and in the Sun Belt area of the United States.

It is estimated that 1 in 20 AKs eventually becomes a squamous cell carcinoma, the vast majority of which, are very slow-growing, indolent, unaggressive, and have an excellent prognosis. Distant metastases are rare. Consequently, among dermatologists, there is an ongoing debate regarding the need to be aggressive or to be somewhat laissez-faire in the approach to treatment of these lesions.

AKs are usually asymptomatic, but they may itch and become tender or irritated.

They are of cosmetic concern to some patients.

Lesions usually appear singly or as multiple discrete, flat or elevated, verrucous, scaly papules. Their texture typically feels gritty or rough to the touch (Fig. 31.1).

AKs often have an erythematous base covered by a white, skin-toned, yellowish, or brown hyperkeratotic scale.

Found chiefly on sun-exposed areas: the face, especially on the nose, temples, and forehead. They are also commonly noted on the bald areas of the scalp (Figs. 31.2 and 31.3), helix of the ears in men (Fig. 31.4), pretibial legs in women (Fig. 31.5), dorsal forearms (Fig. 31.6), dorsal hands (Fig. 31.7), and the sun-exposed areas of the neck.

The vermilion border of the upper lip is another very common site for actinic keratoses (Fig. 31.8).

Extensive involvement of the mucosal lower lip is referred to as actinic cheilitis (Fig. 31.9).

AKs are usually 3 to 10 mm in size and can gradually enlarge, thicken, and become more elevated and thus develop into hypertrophic actinic keratoses (Fig. 31.10) or a cutaneous horn (Fig. 31.11).

Clinically, very small lesions are often better felt than seen. Palpation of these scaly growths reveals a gritty, sandpaper-like texture.

A shave biopsy is performed if the diagnosis is in doubt.

Cellular atypia is present, and the keratinocytes vary in size and shape. Mitotic figures are common.

The histologic changes of individual cells are indistinguishable from those seen in squamous cell carcinomas.