Field Therapy for Actinic Keratoses (Precancers)

Actinic Keratoses Are Precancers Due to Sun Damage

Actinic keratoses are typically small bumps in sun exposed areas of the body that may develop into squamous cell carcinomas. These precancers are very common among people with lighter skin who are more sensitive to sun related skin damage. Actinic keratoses are areas of skin that have had excessive sun exposure, causing cells to mutate. These mutations make the affected skin cells divide more rapidly and can develop into squamous cell carcinoma skin cancers. A quarter of the United States’ population is estimated to have actinic keratosis,^[1] making it the most common skin diagnosis given to those over 45 years of age.^[2]

Treatment of Actinic Keratoses Can Be Directed at Single Lesions or Entire Areas

There are typically two different approaches doctors use to treat actinic keratoses:

• Spot therapy – Each individual actinic keratosis is selectively destroyed. Typically the destruction is performed with extreme cold temperature (liquid nitrogen) or by destroying the lesion with heat (electrodesiccation).
• Field therapy – In this treatment approach, a large “field” of the skin is treated rather than individually selecting for actinic keratoses. This method is typically chosen when there is diffuse sun damage over an area of skin, such as the scalp, face, and arms. Studies have shown that when there are multiple actinic keratoses in an area, it is very likely that this area of the skin has diffuse sun damage.^[3] The assumption is that it is only a matter of time before more actinic keratoses develop in the area, and so a holistic approach of stopping the process before lesions develop is undertaken with field therapy.

How Does Field Therapy Work? 

Field therapy works by several different mechanisms depending on the therapy that is used (Table 1). In all of the cases, the precancerous cells are destroyed and slowed in their ability to divide. 

What Condition Does Field Therapy Treat? 

Field therapy is directed toward the treatment of actinic keratoses. As noted above, actinic keratoses are precancerous lesions that carry a risk to develop into squamous cell carcinoma skin cancers.

How Is The Field Therapy Performed?

Field therapy is performed either with the use of prescribed creams, photodynamic therapy, or through the use of a chemical peel (Table 1). The mode in which the treatment is performed is summarized in Table 2.

*A physician may alter dosing and typical off-label dosing adjustments are indicated in parentheses.

What Are Common Side Effects and Risks of Field Therapy? 

All field therapies will induce redness, irritation, and swelling of the treated sites. The speed with which this improves depends on each of the treatments but will typically last from one to three weeks. There are a few particular side effects for each of the treatments. 

• 5-fluorouracil or imiquimod - Painful skin erosions can form and there is a risk for bacterial infections of any open wounds. 
• Ingenol mebutate - This cream can lead to erosions and there is a risk for bacterial infection. There also may be a small yet increased risk for shingles (herpes zoster) after using ingenol.^[14]
• Photodynamic therapy - Because sunlight contains blue light, the skin can be extremely sun sensitive following treatment. It is generally recommended that anyone getting photodynamic therapy minimizes sunlight exposure (direct or reflected through windows or the ground) for 36 to 48 hours after treatment.
• Chemical peel - Chemical peels can lead to redness, peeling, and scaling of the face in the days following the peel. In people with darker skin, chemical peels pose the risk of causing areas of darker and lighter skin color changes. 

With any of these treatments, if you have a history of cold sores, there is an increased risk of break out during or after field therapy.

What Else Should You Know About Field Therapy?

Field therapy typically needs to be repeated even after successful treatment, as the recurrence rate ranges from 25% to 75%.^[15] Treatments be repeated every one to three years if there is a lot of sun damage and actinic keratoses.