Lentigo maligna (LM) is an in situ variant of melanoma. Our objective was to systematically review clinical and histological clearance and recurrence rates of imiquimod treatment of LM with emphasis on progression to lentigo maligna melanoma (LMM). PubMed, EMBASE and the Cochrane library were searched from inception to May 2015. Articles were included if they described histologically proven LM treated with imiquimod 5% monotherapy or combined with another topical therapy. Analysed outcomes were clinical and histological clearance, recurrence rates and number of LMM. The quality was assessed using the GRADE-like checklist, and results were reported according to the PRISMA Statement. Twenty-six case reports, 11 retrospective studies, three prospective studies and one randomized controlled trial were included. One case report of poor quality was excluded. Complete clinical clearance was seen in 369 of 471 patients (78.3%). Histological clearance was present in 285 of 370 (77%) patients. LMM was diagnosed in nine (1.8%) patients 3.9 months (range 0-11 months) post-treatment. Univariate multinominal logistic regression showed that 6-7 applications/week had a 6.47 greater odds (P = 0.017) of resulting in complete clinical clearance compared to 1-4 applications/week. An intensity of 6-7 applications/week showed a 8.85 greater odds (P = 0.003) of resulting in histological clearance compared to 1-4 applications. Applying imiquimod >60 times during a treatment period of 12 weeks (range 4-36) showed a 7.75 greater odds (P = 0.001) of resulting in histological clearance compared to <60 total applications. In conclusion, a treatment schedule using imiquimod 6-7 applications per week, with at least 60 applications, shows the greatest odds of complete clinical and histological clearance of LM. Imiquimod is an option for patients unfit for or not willing to undergo surgery or radiotherapy. Nine cases of LM progressed to LMM shortly after treatment. Our hypothesis is that these LMM may have been present before starting imiquimod.

The cancer/testis antigens (CTA) are a group of antigens expressed on germ cells of healthy testis and malignant tumors. We studied whether CTA are present on lentigo maligna (LM) and LM melanoma (LMM) samples. Immunohistochemical expression of a panel of CTA (MAGE-A1, A2- A3, NY-ESO-1, PRAME, SSX-2, and a MAGE-A antibody reactive with -A1, -A2, -A3, -A4, -A6, -A10, and -A12) was investigated in formalin-fixed paraffin-embedded samples from LMM (n = 20), LM (n = 8), chronically sun-exposed skin (n = 7), and healthy skin (n = 7). In 4 LMM lesions, the MAGE-A marker was positive. Another 3 LMM lesions were positive for MAGE-A1, MAGE-A2, and MAGE-A3. PRAME was positive in 18/20 LMM and 6/8 LM. We did not find expression of MAGE, NY-ESO-1, or SSX-2 in LM, thereby excluding these CTA as diagnostic markers to discern malignant melanocytes in LM from normal melanocytes. LMM did express MAGE, NY-ESO-1, and SSX-2. If a biopsy from a lesion suspect for LM shows positivity for MAGE, NY-ESO-1, and SSX-2, the lesion may actually be LMM. In contrast, PRAME expression was found in LM at low levels and in LMM at much higher levels, and absent in normal melanocytes. PRAME can potentially be used to discern normal melanocytes from malignant melanocytes.

Presence of preinvasive lesions, especially high-grade lesions, may serve as LC risk markers. LCs occur both at preinvasive lesion sites and elsewhere in the bronchial epithelium or lung parenchyma. Prospective validation of biomarkers and randomized intervention studies are needed to determine optimal management strategies.