James Q. Del Rosso, DO, FAOCD; Valley Hospital Medical Center, Las Vegas, Nevada
Howard Sofen, MD; Dermatology Associates, Los Angeles, California;
Barry Leshin, MD; The Skin Surgery Center, Winston-Salem, North Carolina
TC Meng, MD; James Kulp, BS and Sharon Levy, MD, Graceway Pharmaceuticals, Bristol, Tennessee
Disclosure: Dr. Del Rosso is a consultant, researcher, and speaker for Graceway, PharmaDerm, and Coria. Drs. Sofen and Leshen were investigators for the study and compensated for their services. Drs. Meng and Levy and Mr. Kulp are employed by Graceway. The study was sponsored by Graceway Pharmaceuticals.
Objective: Safety of multiple 16-week courses of imiquimod applied to large areas (>25 cm2) of skin with actinic keratoses. Design: Subjects applied 1 to 6 packets two times per week for 16 weeks; if actinic keratoses were persistent at two months post-treatment, up to two additional courses could be administered within the 18-month study period. Setting: Multicenter, outpatient. Participants: Adults with >4 actinic keratoses on the head, torso, and/or extremities. Measurements: Treatment discontinuations, adverse events, lesion counts. Results: Safety analyses included 551 subjects. At baseline, mean overall treatment area was 625±1114cm2. Overall, the mean days on study was 467±157, and the mean exposure 215±133 packets with 155, 150, and 250 subjects receiving 1, 2, or 3 treatment courses, respectively. Of the 155 subjects (28.1%) who did not complete the study, 20 (3.6%) and 9 (1.6%) were discontinued for adverse events and local skin reactions, respectively. Adverse events related to study drug were reported by 40.5 percent of subjects. The local skin reactions rated as severe reported by the most subjects were erythema (31.4%), flaking/scaling/drying (23.8%), and scabbing/crusting (22.0%). For 525 subjects with analyzable lesion data, the mean baseline lesion count was 45.5±2.4. Overall reduction in target lesion count was 80.2 percent (p<0.0001, 95% CI 77.2–83.3%), with overall complete clearance rate of 36.4 percent and partial clearance rate (>75% reduction) of 68.6 percent. Conclusion: Multiple 16-week courses of imiquimod to treat actinic keratoses were well tolerated and significantly decreased lesions in subjects with extensive actinic keratoses.
(J Clin Aesthetic Dermatol. 2009;2(4):20–28)
Actinic keratoses (AKs) are common cutaneous lesions induced by chronic ultraviolet (UV) light exposure that are early stage precursors to in-situ and invasive squamous cell carcinoma (SCC).[1–3] Chronic UV radiation exposure causes cutaneous immunosuppression, the formation of deoxyribonucleic acid pyrimidine covalent dimers, and mutations in the p53 tumor suppressor gene in keratinocytes resulting in alterations within these keratinocytes, all of which promote the formation of AKs.[4,5] The progression of AK to invasive SCC has been reported to range from as low as 0.025 to as high as 16 percent per year. Although some AKs may regress spontaneously, with a reported regression rate as high as 25 percent over a 12-month period, there are no clinical criteria to predict which AKs will evolve into invasive SCC. Therefore, treatment of AKs and monitoring of therapeutic response and potential disease progression over time are warranted.
Treatment options for AK include physical modalities, such as cryotherapy, curettage, electrodessication, dermabrasion, chemical peels, laser vaporization, surgical excision, and photodynamic therapy as well as topical therapies, such as topical 5-flurouracil, diclofenac, and imiquimod. Imiquimod is a Toll-like receptor agonist that directly activates the innate immune system, resulting in cytokine production; in addition, imiquimod indirectly augments acquired immunity.[10,11] Application of imiquimod to cutaneous lesions, including AKs, is associated with upregulation of genes associated with dendritic cell, cytotoxic T cell, and natural killer cell activation as well as genes associated with apoptosis.[12–14] Imiquimod 5% cream was originally approved in 1997 for the treatment of external genital warts and subsequently for treatment of superficial basal cell carcinoma (BCC). In 2004, the United States Food and Drug Administration (FDA) approved imiquimod 5% cream for the treatment of AK. The approved treatment regimen for AK is application of one packet (250mg of cream) to a 25cm2 area on the face or balding scalp two times per week (2x/wk) for a full 16-week regimen. The pivotal studies conducted for approval were limited as to the treatment location (the face), the treatment area (25cm2), and the treatment duration (one 16-week course). This article reports the safety and efficacy results of an open-label, multicenter study of application of up to six packets of imiquimod 5% cream 2x/wk to AKs, applied to a more extensive body surface area on the head, torso, and/or extremities, for one, two, or three 16-week treatment courses.
Study population. Subjects were required to be 18 years of age or older with at least four clinically typical, discrete, visible, nonhypertrophic AK lesions located within contiguous or noncontiguous locations totaling >25cm2 on the head, torso, and/or extremities. Participants were excluded if they had a dermatologic condition in the treatment area(s) that might be exacerbated by therapy or would impair study assessments, an allergy to imiquimod or cream excipients, or were currently enrolled in another clinical study. Subjects could not have received treatment in the treatment area(s) with imiquimod, psoralens plus UVA, UVB therapy, laser, dermabrasion, or chemical peel within three months, and topical retinoids, topical 5-fluorouracil, topical diclofenac, topical masoprocol, cryotherapy, chemotherapy, surgical excision, photodynamic therapy, curettage, or topical corticosteroids within one month. The above treatments were also prohibited during the study. Selected subjects were enrolled in a pharmacokinetic sub-study that required them to have at least 25 percent total body surface area involvement with AKs. The results of the pharmacokinetic sub-study are reported separately from this article.
At each study center, the study protocol was approved by independent ethics committee(s), either local or central, as applicable. Written informed consent was obtained from each subject before any study-specific procedures were performed. The study was conducted in accordance with international guidelines, recommendations, and requirements for the ethical conduct of clinical studies.
Study design. The total study duration for a subject, including all treatment courses and associated follow-up time, was 18 months. Treatment was 2x/wk for 16 weeks for each treatment course. If AKs within the treatment area(s) had not completely cleared at a two-month post-treatment (PT) visit, the subject was allowed to initiate a second (or third) treatment course (Figure 1) if he or she agreed to do so. A patient who cleared after the first treatment course but had AKs recur within the treatment area during follow up could initiate a second treatment course. At the initial treatment visit, the investigator determined the treatment area(s), which were defined as contiguous or noncontiguous locations of any shape totaling greater than 25cm2 (at initial treatment visit) located on the head, torso, and/or extremities and containing a total of at least four clinically typical, visible, discrete, nonhypertrophic AKs. In subsequent treatment courses, the treatment area(s) could be smaller than in the initial treatment courses, but must have been part of the initial treatment area(s). A body diagram was provided to subjects to assist in consistent application.
Study drug consisted of single-use packets of imiquimod 5% cream (Graceway Pharmaceuticals LLC, Bristol, Tennessee) containing 250mg of imiquimod cream. At the beginning of each treatment course, the number of packets of study drug to be applied (1–6) for each dose was determined by the investigator based upon the total measured treatment area (no more than one packet per 25cm2 of treatment area and no more than 6 packets total per dose). If more than one packet was used, subjects were instructed to use only what was required to cover the treatment area(s). The study drug was dispensed and unused packets collected at the monthly visits during a treatment course. The study drug was applied to AKs, gently rubbed to cover the treatment area(s), allowed to air dry, and removed after approximately eight hours by washing. If the investigator determined all dosing needed to be interrupted for a local skin reaction (LSR) or adverse event (AE), the interruption was considered a rest period; dosing resumed upon satisfactory resolution as assessed by the investigator and with the agreement of the subject. If the investigator determined dosing needed to be interrupted for some, but not all, treatment areas, the interruption was not considered a rest period.
For each treatment course, subjects were seen at initiation; Months 1, 2, and 3 during treatment; at the end of treatment; and two months PT (which may coincide with a treatment initiation visit for next course). Subjects who had complete clearance at a two-month PT visit were seen every three months thereafter for follow up until the end-of-study (EOS) visit. Subjects who had completely cleared, but then had a recurrence in a treatment period could initiate another treatment course only if they could complete a treatment course and the two-month PT visit prior to the EOS visit (Month 18). Interim visits were allowed for safety assessments. The scheduled study visit closest to study Month 18 was considered the EOS visit.
Safety evaluations included recording of AEs, assessment of defined LSRs (erythema, edema, weeping/exudate, flaking/scaling/ dryness, scabbing/crusting, and erosion/ ulceration), skin quality assessments (skin surface roughness/dryness/scaliness, hyperpigmentation, hypopigmentation, degree of scarring, atrophy, and visible photodamage) using a four-point scale (none, mild, moderate, severe), vital sign measurements, and physical examinations. LSRs and skin quality assessments were assessed on a four-point scale (none, mild, moderate, severe), except for erosion/ ulceration, which was assessed on a three-point scale (none, moderate [erosion], severe [ulceration]). AEs were coded using the MedDRA® version 9.0 (Medical Dictionary for Regulatory Activities, a registered trademark of the International Federation of Pharmaceutical Manufacturers and Associations). Efficacy was evaluated by AK lesion counts within the treatment area(s) performed by a qualified dermatologist; a body diagram was used to keep track of the designated treatment areas. The primary measure was the percent change in total AKs in the treatment areas comparing the count at the final PT visit to baseline. Secondary measures included the complete clearance rate, the partial clearance rate (>75% of lesions), change in AK lesion counts, and change in total treatment area(s) size.
The number of subjects was determined per the International Conference on Harmonisation guideline E1A, which suggests that 300 to 600 patients are adequate to observe whether frequently occurring AEs increase or decrease over time and to observe delayed AEs of reasonable frequency. An approximately 45-percent complete clearance rate was observed in the 16-week Phase 3 studies15; in this more severely affected AK population, it was estimated that approximately 300 and 100 subjects would initiate a second and third treatment course, respectively. With this number of subjects, it was estimated an AE with an incidence of 0.6 percent had a 95-percent probability of occurring at least once during a study of 18 months duration.
The study was conducted at 31 study centers in the United States. The first subject was enrolled July 14, 2005, and the last subject completed the study on June 7, 2007. Of the 586 subjects screened, 552 were enrolled, 551 received study drug (1 discontinued prior to dosing, safety population [SP]), and 525 had baseline lesion counts and at least one scheduled primary efficacy assessment at a two-month PT visit (efficacy population [EP]). Of the SP subjects, 396 (71.9%) completed the study while 155 (28.1%) did not; most of those who did not complete the study discontinued during Course 1 (99) (Table 1). The most common primary reason for not completing the study was “personal” (68 subjects); 29 subjects discontinued study for “adverse events” (20) or “local skin reactions” (9) (Table 1). Subjects were predominantly male (79.3%) with a mean age of 67.5 years, Caucasian (100%), and predominantly Fitzpatrick skin type II (44.1%) or I (33.9%) (Table 2). For the SP, the mean total treatment area was 625.3cm2, and the mean AK-involved percent body surface area was 7.4 percent (Table 2).
Safety. During the study, 39 (7.1%) subjects experienced 53 serious AEs, including six deaths; none of the serious AEs or deaths was considered probably related or related to the study drug. Of the 20 (3.6%) subjects who discontinued the study for AEs, 10 discontinued for events considered probably related or related to study drug, including (subject may have had more than one) pruritus, chills, headache, wheezing, anorexia, anxiety, panic attack, pain, myalgia, arthralgia, hematospermia, application-site bleeding, and application-site pruritus; most were moderate in intensity and none were severe. Of the 9 (1.6%) subjects who discontinued for an LSR, 1, 3, and 4 subjects reported mild, moderate, and severe LSRs in intensity, respectively (1 not recorded). Of these 29 subjects discontinuing for AEs or LSRs, 23, 4, and 2 subjects discontinued during/following the first, second, and third treatment course, respectively. An additional five subjects discontinued treatment due to an AE, but completed the study; four were for events considered probably related or related to study drug, including AEs of fatigue, headache, cough, pain/body aches, eye disorder, application-site inflammation, and application-site pain (subject may have had more than 1).
As subjects underwent additional treatment courses, fewer subjects required rest periods; 107/550 (19.5%), 27/400 (6.8%), and 13/251 (5.2%) of subjects required at least one rest period during Courses 1, 2, and 3, respectively. This may have been affected by the subjects discontinuing during Course 1 for reasons related to tolerance. Within a treatment course, there appeared to be a slight increase in subjects requiring a rest period as the number of packets applied per application increased. For example, at least one rest period was required by 14.7% (22/150), 20.7% (25/169), and 21.6% (50/231) of subjects in Course 1 who applied 1 to 2, 3 to 4, and 5 to 6 packets per application, respectively.
At least one AE considered probably related or related to study drug was reported by 40.5 percent of subjects (Table 3). The AEs reported by the most subjects in this category were application-site events, including application-site pruritus (22.0%), application-site irritation (8.5%), and application-site pain (5.3%). Of the AEs of special interest (i.e., those that might be consistent with exposure to circulating levels of cytokines from local spillover or from direct systemic induction), the most frequently reported were fatigue (4.4%), headache (2.7%), and myalgia (2.2%). Independent of investigator-assessed causality, at least one AE was reported by 85.7 percent of subjects. AK (30.5%) and other cutaneous lesions associated with chronic UV radiation exposure, including SCC (15.1%) and BCC (14.9%), were among the AEs reported by the most subjects in this category (Table 3). The incidence for some AEs (independent of causality assessment) appeared to increase with the number of treatment courses to which the subjects were exposed. This pattern may reflect a time-on-study bias as some subjects who did not receive additional courses had discontinued earlier from the study and therefore had less time to observe AEs. It may also reflect increased underlying AK severity. While unlikely, an actual relationship to increased cumulative study drug exposure in those receiving more courses of therapy could not be entirely excluded. Overall, however, within a treatment course, the proportion of subjects with AEs was highest during Course 1 (72.4%), decreasing to 62.8 percent and 55.6 percent during Courses 2 and 3, respectively. Within a treatment course, the incidence of specific AEs appeared to be similar regardless of the number of packets applied. AEs in the category of general disorders and administrative-site conditions, mainly application-site pruritus and application-site irritation, were reported with greater frequency during Course 1 (34.9%) than in Courses 2 or 3 (14.0% and 9.5%, respectively). No trends were observed in these AEs by treatment course, number of courses exposed, or number of packets assigned per dose.
In general, all subjects reported LSRs during the study. The LSRs rated as severe that were reported by the most subjects were erythema (31.4%), flaking/scaling/dryness (23.6%), and scabbing/crusting (22.0%) (Table 4). Within each treatment course, LSRs tended to increase over predose levels during the initial months of treatment and returned to baseline levels or below by the end of treatment. Overall, mean LSR intensity decreased in each subsequent treatment course. Severe-grade LSRs (any) were reported by more subjects for the torso region (48.9%) compared to the head (27.5%) or extremities (38.5%). For all regions, erythema was the LSR that was rated as severe by the most subjects (47.7%, 18.2%, and 26.2% for torso, head, and extremities, respectively), followed by flaking/scaling/ dryness (20.5%, 14.8% and 23.7% for torso, head, and extremities, respectively) and scabbing/crusting (19.3%, 13.9%, and 20.9% for torso, head, and extremities, respectively). There were no clinically meaningful changes from baseline in the vital sign measurements or clinical laboratory values. There were no unexpected findings in physical examinations during the study.
For the subjects with complete dosing information, the mean number of days on study was 467 and the mean number of packets used was 215 (2683mg imiquimod) (Table 4). Mean number of days on study was shorter for those treated with only one course mainly due to discontinuations; as expected, the number of packets used increased with number of courses (Table 5). Overall, 88 percent of subjects were considered compliant (applied ?60% of assigned dose); for subjects with data, the compliance rate was 93 percent and >90 percent for each of the treatment courses.
Efficacy. For the EP population at baseline the mean AK lesion count was 45.5 (standard error 2.4) with a median of 29.0 (Table 2). The overall mean reduction in lesion count at the final follow up compared to baseline was 80.2 percent (p<0.0001; 77.2–83.3%; 95% CI) (Figure 2). The overall median reduction in AK lesions was 93 percent (p<0.0001) and the final median AK lesion count was 2. When evaluated by the treated anatomic site, the mean percent reductions in lesion count after each treatment course and overall tended to be slightly lower for the extremities as compared to the head and the torso (Figure 2). Subjects with less than the median treatment area size (median baseline lesion count of 18 lesions) had a higher rate of complete clearance (46.3% versus 26.9%) and higher percent reduction in AK lesions (median 97% vs. 89%) compared to subjects above the median treatment area size (median baseline lesion count of 47 lesions). No relevant differences in efficacy were observed in subgroup analyses by gender, race, age, or skin type (data not shown).
Overall, 36.4 percent of subjects had complete clearance and 68.6 percent of subjects had partial clearance (>75% reduction in lesions) (Figure 3). For the subjects entering each treatment course, the complete clearance rates were 18.3 percent, 20.4 percent, and 18.4 percent after Courses 1, 2, and 3, respectively (Figure 3). Complete and partial clearance rates after each treatment course, and overall, tended to be slightly greater for the torso than for the head or the extremities (Figure 3).
The total treatment area size (cm2) decreased from a mean and median of 624 and 288cm2 at baseline to 123 and 5cm2 at the final follow up, respectively. The median total treatment areas for subjects entering Courses 1, 2, and 3, which would exclude the subjects who completely cleared in the prior treatment course or were lost to follow up, were 288, 120, and 104cm2, respectively. Acknowledging the limitations of the subjects who were excluded with each subsequent course due to complete clearance of AKs or withdrawals, the progressive decrease total treatment area suggests continued benefit with each additional treatment course.
In general, within each treatment course, a significant decrease from baseline was observed in mean skin quality intensity scores for most skin quality parameters (data not shown), consistent with clinical improvements. This observation was consistent across the three treatment cycles and all treatment sites (i.e., head, torso, and extremities).
This study represents the largest and longest prospective experience reported on the long-term use of imiquimod 5% cream in patients with AK. More than 500 enrolled subjects were treated with up to three treatment courses of 16 weeks, for a total of up to 48 weeks of treatment over 18 months. In addition, the dosing and the treatment area was much greater than for the approved dosing for AK, with up to six packets (250mg cream each) applied per dose twice weekly in this study, a median of 197 total packets used, and a baseline median treated area of 285cm2. With this extensive exposure, treatment was generally well tolerated. There were no serious AEs attributed to study drug and only 23 (4.2%) subjects discontinued treatment for AEs attributed to study drug or for LSRs. Cutaneous skin lesions, such as AK, BCC, and SCC, were among the AEs reported by the most subjects, consistent with the higher risk for these conditions expected in this population due to association with chronic UV radiation exposure. Otherwise, the AEs attributed to study drug by the investigator were generally consistent with those reported in previous clinical studies of imiquimod. No correlation was observed between the number of AEs reported and the total size of AK treatment area, nor with the number of packets utilized.
While there are limitations in comparisons due to the different study designs, including open label versus placebo controlled, the incidences of influenza-like AEs, such as fatigue (6.2%) and myalgias (3.1%), but not headache, were higher in this study than that reported in the 2x/wk for 16 weeks single-treatment course studies in AK (i.e., 1% and <1%).[15,17] The rates of application-site reactions reported by most subjects in this study (independent of causality attribution)—application-site pruritis (23.0%), application-site irritation (8.7%), and application-site pain (5.4%)—were slightly higher than for the placebo-controlled studies (i.e., 20%, 2%, and 3%, respectively).15,17 Similarly, the incidences of severe grade LSRs in this study were higher than those reported for a single treatment course (i.e., erythema [31.4 vs. 18%], flaking/scaling/dryness [23.8 vs. 7%], and scabbing/crusting [22.0 versus 8%]). These increases were not unexpected based on the more extensive exposure with respect to increased dose applied, longer study duration, multiple treatment courses, and multiple treatment areas assessed. However, these differences in safety profile did not appear to result in a marked increase in discontinuations attributed to study drug. Overall, no unexpected safety issues were observed.
The primary efficacy variable—the percent reduction in total AK lesion count from baseline to the final follow-up visit—was highly significant with a mean and median percent reduction of 80.2 percent and 93 percent, respectively (both p<0.0001). This is especially noteworthy considering that at baseline, subjects had numerous AKs (mean 45.5, median 29.0) in the overall treatment area, which could include up to three separate body sites. The mean reduction in lesion count after a single treatment course was slightly lower while the overall lesion reduction after multiple treatment courses was slightly higher than those observed in the Phase 3, placebo-controlled studies of a single, 16-week treatment course, where the mean reduction was 69.5 percent and the median reduction was 85.7 percent (personal communication, James Lee, Graceway Pharmaceuticals, December 8, 2008). In addition to this endpoint, the more traditional endpoints of complete clearance and partial clearance (?75% reduction in lesion number) were also determined in this study. Overall, 36.4 percent of subjects were considered completely clear at the final follow-up visit, with 18.3 percent of subjects achieving complete clearance after Course 1. Both of these complete clearance rates were lower than those observed in studies with a single, 16-week treatment course, where 44 to 46 percent of subjects had achieved complete clearance.[15,17] They were also lower than those reported in studies using one or two sequential courses of 3x/wk dosing for four weeks; complete clearance was observed in 26.8 to 37.2 percent and 53.7 to 55.0 percent of subjects after one course of treatment, and overall, respectively.[18,19] However, the hurdle to achieve complete clearance in this study was very high, given the larger number of AKs treated (no preset limit in number), and the requirement to achieve complete clearance simultaneously at multiple treatment sites in up to three treated body regions (head, torso, and/or extremities). In contrast, the prior studies only evaluated a single discrete anatomic location in each subject, with a maximum treatment area of 25cm2, and a maximum of eight AK lesions treated (actual median baseline lesion number was approximately 6).[15,18,19]
Acknowledging the limitations of the effect of subject dropouts over time, it appeared that with each additional treatment course there was additional benefit with respect to the number of subjects achieving complete clearance or partial clearance, the reductions in treatment area size, and the reductions in AK lesion counts. Comparison of incremental benefit with respect to number of treatment courses was limited by the study design in that subjects were not prospectively randomized to the number of treatment courses; proceeding to another treatment course was dependent on the clearance status after the prior treatment course. The noncomparative study design also has limitations—efficacy assessments and safety reporting may have been influenced by knowledge that subjects were on active drug.
In summary, up to 48 weeks of 2x/wk dosing with imiquimod 5% cream, involving up to six sachets per dose applied to large areas of skin with AK involvement, including the head, torso, and/or extremities, was considered well tolerated overall. No new safety findings were observed over the 18 months of the study. There was evidence of clinical benefit with respect to overall percent lesion reduction. Although complete clearance rates were lower than in prior placebo-controlled studies, the inclusion criteria in this study enrolled subjects warranting more extensive AK treatment than in previous studies. Complete and partial clearance of AKs was achieved for a meaningful proportion of subjects after each treatment course in a population with extensive AKs.
The authors would like to acknowledge the other study investigators: Amir Bahoghli, Vienna, VA; Kenneth Beer, West Palm Beach, FL; Miriam Bettencourt, Henderson, NV; Neal Bhatia, Milwaukee, WI; Michael Bukhalo, Arlington Heights, IL; Zoe Draelos, High Point, NC; Paul English, Phoenix, AZ; Stephen Eubanks, Denver, CO; Scott Fretzin, Indianapolis, IN; Caron Meg Grin, New Britain, CT; Kenneth Gross, San Diego,CA; Robert and Rene Koppel, Metairie, LA; Steven Miller, San Antonio, TX; Angela Moore, Arlington, TX; Adnan Nasir, Raleigh, NC; Ethan Nguyen, Riverside, CA; Laura Ostezan, Reno, NV; Tania Phillips, Boston, MA; Andrew Pollack, Fort Washington, PA; Joseph Raoof Tooraj, Encino, CA; David Rodriguez, Coral Gables, FL; Franz J. Stadler, Reno, NV; Eduardo Weiss, Hollywood, CA; William Werschler, Spokane, WA; Hector Wiltz, Miami, FL; Paul Yamauchi, Santa Monica, CA; John Fenyk, Jr., Chaska, MN; Phoebe Rich, Portland,OR. In addition, the authors would like to thank the study personnel and the patients of each of the study centers. Finally, the authors acknowledge Li Liu and James Wu for assistance with statistical analyses and Jack Furst for reviewing the manuscript.
1. Frost CA, Green AC. Epidemiology of solar keratoses. Br J Dermatol. 1994;131:455–464.
2. Schwartz RA. Premalignant keratinocytic neoplasms. J Am Acad Dermatol. 1996;35:223–242.
3. Yantsos VA, Conrad N, Zabawski E, Cockerell CJ. Incipient intraepidermal cutaneous squamous cell carcinoma: a proposal for reclassifying and grading solar (actinic) keratoses. Semin Cutan Med Surg. 1999;18:3–14.
4. Marrot L, Meunier JR. Skin DNA photodamage and its biological consequences. J Am Acad Dermatol. 2008; 58(Suppl 2):s139–s148.
5. Aubin F. Mechanisms involved in ultraviolet light-induced immunosuppression. Eur J Dermatol. 2003;13:515–523.
6. Glogau RG. The risk of progression to invasive disease. J Am Acad Dermatol. 2000;42:s24–s25.
7. Marks R, Foley P, Goodman G, Hage BH, Selwood TS. Spontaneous remission of solar keratosis: the case for conservative management. Br J Dermatol. 1986;115:649–655.
8. Heaphy MR. The nature of solar keratosis: a critical review in historical perspective. J Am Acad Dermatol. 2000;43:138–150.
9. Dinehart SM. The treatment of actinic keratosis. J Am Acad Dermatol. 2000;42:25–28.
10. Hemmi H, Kaisho T, Sato S, et al. Small antiviral compounds activate cells via the TLR7 MyD88-dependent signaling pathway. Nat Immunol. 2002;3:196–200.
11. Gibson SJ, Lindh JM, Riter TR, et al. Plasmacytoid dendritic cells produce cytokines and mature in response to the TLR7 agonists, imiquimod and resiquimod. Cell Immunol. 2002;218:74–86.
12. Lysa B, Tartler U, Wolf R, et al. Gene expression in actinic keratoses: pharmacological modulation by imiquimod. Br J Dermatol. 2004;151:1150–1159.
13. Ooi T, Barnetson RS, Zhuang L, et al. Imiquimod-induced regression of actinic keratoses is associated with infiltration by T lymphocytes and dendritic cells: a randomized controlled trial. Br J Dermatol. 2006;154:72–78.
14. Torres A, Storey L, Anders M, et al. Immune-mediated changes in actinic keratosis following topical treatment with imiquimod 5% cream. J Transl Med. 2007;5:7–25.
15. Lebwohl M, Dinehart S, Whiting D, et al. Imiquimod 5% cream for the treatment of actinic keratosis: results from two Phase III, randomized, double-blind, parallel group, vehicle-controlled trials. J Am Acad Dermatol. 2004; 50:714–721.
16. Guideline for Industry. The Extent of Population Exposure to Assess Clinical Safety: For Drugs Intended for Long-term Treatment of Non-Life-Threatening Conditions. ICH-E1A, March 1995.
17. Aldara® (imiquimod cream, 5%) [package insert]. Bristol, TN: Graceway Pharmaceuticals, LLC; November 2007.
18. Jorizzo J, Dinehart S, Matheson R, et al. Vehicle-controlled, double-blind, randomized study of imiquimod 5% cream applied 3 days per week in one or two courses of treatment for actinic keratoses on the head. J Am Acad Dermatol. 2007;57:265–268.
19. Alomar A, Bichel J, McRae S. Vehicle-controlled, randomized, double-blind study to assess safety and efficacy of imiquimod 5% cream applied once daily 3 days per week in one or two courses of treatment of actinic keratoses on the head. Br J Dermatol. 2007;157:133–141.