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. 

Table 1. Field Therapy Options

Topical Drug or Procedure	Brand Name	How does it work?	Where is it performed?
Topical Drug: 5-fluorouracil	Efudex®, Carac	5-fluorouracil mimics DNA to incorporate into and destroy rapidly dividing cells	By the patient at home
Topical Drug: Imiquimod	Aldara, Zyclara	Imiquimod activates the immune system,[4] stimulating it to destroy the mutated cells	By the patient at home
Topical Drug: Diclofenac	Solaraze	Diclofenac blocks production of prostaglandins and may decrease development of new blood vessels and cell division;[5] the exact way diclofenac works remains unknown	By the patient at home
Topical Drug: Ingenol mebutate	Picato®	Ingenol directly destroys actinic keratosis lesions and it also activates immune cells (neutrophil) to destroy the actinic keratoses lesions[6]	By the patient at home
Procedure: Photodynamic Therapy	Not applicable	Amino-levulinic acid is applied to the skin and is metabolized to a blue-light-sensitive chemical known as protoporphyrin IX; the precancerous cells are more active and take up blue-light-sensitive chemicals faster than normal cells during the incubation phase, allowing for the precancerous cells to be preferentially destroyed when exposed to blue-light	At the physician’s or practitioner’s office
Procedure:  Chemical Peel	Not applicable	A chemical peel strips away the surface of the skin based on the type of peel that is used; the chemical peel needs to at least remove the epidermis to be effective and this directly destroys the actinic keratoses; additional superficial peels will not be effective	At the physician’s or practitioner’s office

 

 

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.

Table 2. Details on How Field Therapy is Dosed and Delivered*

Drug or Procedure	How Is The Treatment Typically Dosed?
5-fluorouracil	Efudex: Cream is applied twice daily for two to four weeks until the development of erosions[7] Carac: Cream is applied once daily for up to four weeks[8]
Imiquimod	Aldara: Cream is applied twice a week for 16 weeks[9] Zyclara: Cream is applied once daily for two-week treatment cycles separated by a two-week period of no treatment[10]
Diclofenac	Solaraze: Cream is applied twice daily for 60 to 90 days[11]
Ingenol mebutate	Picato: Scalp and Face - Ingenol 0.015% gel is applied once daily for three days Picato: Trunk and Arms/Legs – Ingenol 0.05% gel is applied once daily for two days
Photodynamic Therapy	Aminolevulinic acid is applied to the skin and incubated for 14 hours prior to exposure to blue LED lights for 1,000 seconds (many practitioners have shortened the incubation to one hour prior to blue-light exposure[12])
Chemical Peel	Chemical peels with Jessner’s solution and 35% TCA peels[13]

*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.