Actinic (solar) keratosis (AK)

Actinic keratosis (AK), sometimes referred to as solar keratosis or sun spots, is a pre-cancerous skin condition that appears as a dry, scaly sometimes hyperkeratotic lesion as a result of prolonged and repeated sun exposure. The typical AK lesion is a dry, scaly, skin-coloured, reddish-brown or yellowish-black lesion. The onset of AK is subtle and therefore often passes unnoticed for some time before diagnosis. AK lesions are usually found on chronically sun-exposed sites of the head and neck and the dorsa of the hands and forearms.

If left untreated, AKs can progress into thickened lesions and subsequently develop into invasive SCC. There is an emerging view that AK is an intra-epidermal malignancy and it exists in a continuum with squamous cell carcinoma (SCC), the second leading cause of skin cancer deaths in the US, so that AK will become SCC when dermal invasion occurs. The American Academy of Dermatology reports that 40% of all SCCs begin as AKs.

The majority of patients who have an AK lesion will have multiple lesions and further lesions will become clinically evident in the future. Thus an AK patient can face a lifetime of treatment. AKs are the most common pre-cancerous skin lesions worldwide and the treatment of AKs is the most common dermatologic procedure performed in the out-patient setting.

The National Ambulatory Medical Care Survey (NAMCS) reports 5.6 million office visits annually⁽¹⁾, while a 2005 study by the Lewin Group, in the US each year there are 8.2 million office visits for the treatment of AK. The Lewin group also suggests AK affects more than 58 million Americans with an annual cost to the US healthcare system for the treatment and management of AK equal to US$1.1 billion in 2004⁽²⁾.

The worldwide prevalence of AK is highest in Australia with at least one lesion predicted to occur in 40-60% of all Australian adults⁽³⁾.

Current treatments

Currently, cryotherapy, applying a cryogen, or extreme cold, for a sufficient period of time to destroy the lesion, is the most common treatment alternative used for AK. It is used as the sole approach in approximately 75% of the treatments for AK lesions, and in combination with topical drugs in approximately 9% of the treatments.

Topical drugs are used alone in approximately 16% of AK treatments. Current topical therapies include imiquimod (Aldara), 5-flourouracil (Efudex, Carac, Fluoroplex, etc) and diflenac (Solaraze).

We believe that existing topical therapies for AK, while successful in the marketplace, face barriers to broader adoption. The primary and most significant limitations of existing topical agents are the generally long courses of therapy, which can range from 2 weeks to 16 weeks, and the unsightly side effects of these topical agents, which may persist in the treatment area throughout the course of treatment. We believe these limitations result in general patient dissatisfaction and poor patient compliance with treatment regimens, which ultimately can result in poor treatment outcomes.

We believe that treatment of AK will continue to grow primarily as a function of factors such as:

• growth in the incidence of AK;
• better awareness of AK, sun damage and skin cancer, including the recognition of the benefits of early intervention and prevention of progression to skin cancer;
• a developing understanding among clinicians that topical agents for the treatment of AK may treat both clinically obvious lesions and other lesions that may not yet be visible; and
• general patient preference for less invasive and more cosmetically acceptable treatment alternatives.

1. US office visits for AK, NAMCS database (Avg. for 2001-2005)
2. Lewin Group, The Burden of Skin Diseases 2005
3. Supplement to The Journal of Family Practice, May 2006