An aging population that is living longer, in an atmosphere with a declining ozone layer and with more outdoor and leisure time to bask in this ultraviolet environment, has led to a dramatic increase in sun-related skin damage (dermatoheliosis) and precursors to skin cancer such as solar keratoses. It is estimated that 60% of predisposed people older than 40 years have at least one solar keratosis, and many of them have new solar keratoses each year.

Solar keratosis, also commonly known as actinic 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 controversial. What is accepted, however, is that solar keratoses have the potential to develop into invasive squamous cell carcinomas.

Solar keratoses are more common in men, 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 solar keratosis, as with all of the skin cancers described in this chapter, is highest in Australia and in the Sun Belt of the United States.

It is estimated that 1 in 20 lesions eventually becomes squamous cell carcinoma. It is also accepted that the invasive carcinomas that develop from these actinic keratoses are of a very slow-growing, indolent, unaggressive type, and the prognosis usually is excellent. Distant metastases are extremely rare. Consequently, among dermatologists, there is an ongoing debate regarding the need to be aggressive or laissez-faire in the approach to these lesions.

The development of solar keratoses, which is directly proportional to sun exposure, is seen in people who are fair-skinned, burn easily, and tan poorly.

These lesions are rare in dark-skinned persons.

Lesions usually appear as multiple discrete, flat or elevated, verrucous, scaly lesions. Their texture typically feels rough to the touch (Fig. 22.1).

They typically have an erythematous base covered by a white, yellowish, or brown scale (hyperkeratosis) (Fig. 22.2).

Lesions are usually 3 to 10 mm in size and can gradually enlarge, thicken, and become more elevated and thus develop into a hypertrophic solar keratosis (Figs. 22.3 and 22.4) or a cutaneous horn (Figs. 22.5 and 22.6).

A cutaneous horn is a hornlike projection of keratin. In addition to solar keratoses, warts and squamous cell carcinomas in situ (Bowen’s disease) may also produce a cutaneous horn on their surface.

Sometimes, solar keratoses are tan or dark brown (pigmented solar keratosis) (Fig. 22.7) and are often clinically indistinguishable from a solar lentigo (see Fig. 21.4)

In time, a solar keratosis may develop into a squamous cell carcinoma.

Solar keratoses are most often seen on a background of sun-damaged skin.

They are 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 and the tops of the ears in men, the dorsa of the forearms (Fig. 22.8) and the dorsa of the hands, the “V” of the neck, and the neck below the occipital hairline and below the ears.

The vermilion border of the upper lip is another very common site for solar keratoses (Fig. 22.9).

They may also occur on any area that is chronically or repeatedly exposed to the sun, such as the legs in women.

Extensive involvement of the mucous membranes of the lower lips (generally the lower lip) is known as actinic cheilitis (Fig. 22.10).

Solar keratoses are usually asymptomatic, but they may itch and become tender or irritated. Patients often report one or several “dry” scaly bumps on sun-exposed areas that do not respond to moisturizers.

They are of cosmetic concern to many patients.

They may regress spontaneously.

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

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

Squamous cell carcinoma (SCC) is a malignant epithelial tumor arising from keratinocytes of the epidermis.

It is the second most common type of skin cancer. SCC is diagnosed much less frequently than basal cell carcinoma (BCC), but it carries a risk of metastasis. It occurs in an older age group than does BCC.

Although it is very rare in dark-skinned persons, SCC can be more aggressive in these individuals.

The majority of SCCs arise in solar keratoses (see earlier discussion). Such SCCs that develop from solar keratoses are slow growing, minimally invasive, and unaggressive, and the prognosis is usually excellent because distant metastases are extremely rare.

An SCC may appear de novo without a preceding solar keratosis.

When a metastasis from a cutaneous SCC (non–mucous membrane) does occur, it is more likely to result from lesions that appear on the ears or on the vermilion border of the lips, from lesions that are poorly differentiated, from recurrent lesions, or from tumors larger than 2 cm in diameter.

Also apt to be more aggressive are SCCs that may occur from causes other than sun exposure. For example, a SCC may arise in long-standing scars or from sites previously exposed to ionizing radiation and long-term exposure to psoralen and ultraviolet A light (PUVA) (see Chapter 3, “Psoriasis”). A SCC may also emerge from pre-existing human papilloma virus infection (verrucous carcinoma), in the skin of organ transplant recipients, or chronic inflammatory lesions (e.g., cutaneous lupus erythematosus), as well as cutaneous ulcers (e.g., venous stasis ulcers) or other nonhealing wounds.

As with solar keratosis and BCCs (see later discussion), SCC is related to sun exposure and is noted more frequently in those with a greater degree of outdoor activity.

Lesions appear as papules, plaques, or nodules (Fig. 22.12) that grow slowly.

Lesions are scaly or ulcerated.

Lesions may have a smooth or thick hyperkeratotic surface (Fig. 22.13).

As with solar keratoses, an SCC may also produce a cutaneous horn on its surface.

An SCC may appear as a reddish brown nodule. It may, at times, be indistinguishable from a hypertrophic solar keratosis or a BCC.

Tumors may ulcerate when they are neglected (Fig. 22.14).

Lesions occur in the same locations as do solar keratoses: sun-exposed areas such as the face, the dorsa of the forearms and hands, and the “V” of the neck.

In men, SCCs tend to arise on the bald areas of the scalp and on the tops of the ears as well as the posterior neck below the occipital hairline.

In women, lesions tend to occur on the legs as well as other relatively sun-exposed locations.

In individuals of African origin there is an equal frequency in sun-exposed and unexposed areas.

Most SCCs are asymptomatic, although bleeding, pain, and tenderness may be noted.

Slow-growing, firm papules with the ability to produce scale (keratinization) tend to be more clearly differentiated and less likely to metastasize.

Softer, nonkeratinizing lesions are less well differentiated and are more likely to spread (Fig. 22.15).