Topical imiquimod successful in treating lentigo maligna, in certain settings

Key Points

Atlanta - The use of topical imiquimod can be beneficial in the treatment and management of lentigo maligna (LM), but knowing the scenarios and settings in which to use the topical immunomodulator is key in achieving successful, safe treatment outcomes.

Topical imiquimod is readily used and approved for the treatment of actinic keratoses on the face and superficial basal cell carcinoma. Off-label, imiquimod can be useful in a number of instances, including LM or melanoma in situ.

Though effective for this indication, solid studies on imiquimod for the treatment of LM are few and far between. The clearance rates in most published studies are based predominantly on clinical evaluation without any histologic correlation, Dr. Zwald says.

Moreover, a standardized treatment regimen of imiquimod for LM is lacking, and most of the studies only have very small patient cohorts with short-term follow-ups, the longest of which is almost out to five years (Meurs TV, Van Doorn R, Kirtschig G Dermatol Surg. 2010;36(6):853-858). This study looked at performing biopsies in LM patients with standard follow-up post-clearance clinically and histologically of LM lesions.

"The histology is extremely important because even if LM is not clinically apparent, that does not necessarily mean that you have histologic clearance. Therefore, it is exceptionally important that follow-up is done and that biopsies are taken around the site of the original lesion," Dr. Zwald says.

Recurrence rates

According to Dr. Zwald, both the recurrence rates of LM following surgery and following imiquimod treatment are unacceptably high, begging much need for improvement on this front. Therefore, until a more optimal therapeutic approach is found resulting in significantly improved clearance rates, Dr. Zwald says she believes a combination therapy of surgery and imiquimod may be the best therapeutic approach to date.

"Using imiquimod as an adjunctive treatment to surgery may in certain instances be the most optimal treatment approach, when feasible. Challenging lesions could be best treated with a combination of imiquimod followed by surgical removal or vice versa, depending on the surgeon's chosen technique," Dr. Zwald says.

In a patient in whom a large LM lesion recurs following surgery, one could use imiquimod postop around the surgical reconstruction site, apply it widely to the area once the surgical site has healed and then follow the patient. Imiquimod used after surgery could also help to ensure positive margins and hopefully reduce the risk of recurrence.

Conversely, imiquimod could be used prior to surgical excision in order to reduce the size of the lesion, therefore minimizing surgical intervention. There is some concern, however, that this approach may result in skipped areas and inadvertently evolve or change the LM lesion into a discontiguous tumor, which could potentially negatively impact the success of future attempted surgical clearance procedures.

"I believe that the postop use of imiquimod is extremely beneficial and safer in terms of achieving a true clearance of the LM lesion," Dr. Zwald says. "Also, imiquimod typically causes a pronounced inflammatory reaction and one would have to wait for that reaction to subside and the area to heal before embarking on a surgical clearance."

According to Dr. Zwald, not only is valuable time lost by using imiquimod before surgery; it can be extremely difficult for a histopathologist to accurately discern and differentiate between inflamed cells and abnormal melanocyte proliferation when looking at actively inflamed tissues.

"Whether used before or after surgery, imiquimod should be applied for at least three months in LM lesions and topical treatment can be optimized by occlusion. Though effective for the treatment of LM, clinicians must remember that this is melanoma in situ and because some lesions may contain an unrecognized invasive component, imiquimod should be used with extreme caution," Dr. Zwald says.

Disclosures: Dr. Zwald reports no relevant financial interests.