Amelanotic melanoma: An unusual case

Key Points

Worcester, Mass. - When faculty members of University of Massachusetts School of Medicine, Worcester, treated a 60-year-old female amelanotic lentigo maligna patient with imiquimod, they were surprised to find that the treatment, though failing to affect the cancer, produced pigment at the treatment site, according to a new case study.

Laura Capaldi, M.D., dermatology resident at the University of Massachusetts and lead author of this unpublished study, says the woman presented for evaluation of a sporadically bleeding area on her left nasal sidewall. She denied any edema, pruritus or pain over the area and had no history of skin cancer or other malignancy.

What met the eye

"Wood's lamp examination revealed no pigment. The differential diagnosis included actinic keratosis and squamous cell carcinoma in situ," Dr. Capaldi tells Dermatology Times.

Histopathologic examination of the lesion revealed a severely atypical lentiginous melanocytic proliferation with adnexal extension consistent with an amelanotic lentigo maligna. Dr. Capaldi and colleagues performed scouting biopsies to better delineate the tumor's borders. Histology of the scouting biopsies revealed multiple areas of amelanotic lentigo maligna, along with areas of actinic keratosis and squamous cell carcinoma in situ.

The patient, according to Dr. Capaldi did not want to have surgery, so University of Massachusetts dermatologists treated her with imiquimod, a therapy that has been shown in case reports and case series to successfully treat such lesions.

The patient applied imiquimod nightly for 30 days.

Unexpected findings

"At follow-up there was a 0.5 cm by 0.5 cm hyperpigmented macule at the site of the first biopsy," Dr. Capaldi says.

"Repeat biopsy revealed residual lentigo maligna. So, Mohs micrographic surgery was performed to treat the tumor, resulting in a 3.0 cm by 2.6 cm defect that was repaired using a full-thickness skin graft. She remains recurrence-free one year following the procedure."

The case report is interesting, Dr. Capaldi says, not only because of the failed attempt with imiquimod treatment, but also because the treatment produced pigment where there was none.

"The relationship between treatment with imiquimod and pigment production is not clear, but it is interesting ... because it was something that we did not predict," she says.

Although this is only one case and imiquimod still represents a nonsurgical option in the treatment of patients with amelanotic melanoma, senior author Jeremy Bordeaux, M.D., M.P.H., a Mohs micrographic surgery and cutaneous oncology fellow at the University of Massachusetts School of Medicine, says, "Clinicians should be very careful when treating lentigo maligna with imiquimod. These patients require frequent clinical follow-up and a low threshold for biopsy."