Abstract
This study examines melanocyte density counts in imiquimod-treated lentigo maligna and negative control biopsy specimens to determine if there was a measurable difference in melanocyte density.
Lentigo maligna (LM) is the most common subtype of melanoma in situ, usually occurring in the head and neck regions. Several treatment approaches include wide local excisions, staged excisions (confirmation of negative histologic margins prior to surgical reconstruction), radiotherapy, or topical imiquimod 5% cream. The distinction between the surgical border of LM and surrounding background melanocytic hyperplasia common to chronically sun-exposed skin can be ambiguous. Of all the histologic features of LM, only melanocyte density counts (MDC) are statistically significant in making a distinction between LM and background melanocytic hyperplasia. In 1 study, the mean (SD) MDC for the negative control group was 25.6 (9.3) compared with 82.7 (29.3) cells per 400 × magnification for LM. The average margin requirement for LM removal is reportedly 7.2 mm. When used in the neoadjuvant setting, topical imiquimod 5% cream enables the removal of most LM tumors with 2-mm margins. Gautschi et al reported that the risk for local recurrence after topical imiquimod treatment correlates with the total number of melanocytes per millimeter in the original biopsy specimen. We sought to evaluate MDCs in imiquimod-treated LM and negative control biopsy specimens to determine if there was a measurable difference in melanocyte density.
Methods
The institutional review board of the University of Utah School of Medicine approved this prospective study of 52 cases of LM treated with off-label neoadjuvant topical imiquimod 5% cream 5 days per week for 8 weeks followed by conservative staged excisions with 2-mm margins. Because the study was conducted along standard-of-care guidelines, informed consent was not required. All patients were treated by 1 Mohs surgeon at the Huntsman Cancer Institute at the University of Utah School of Medicine. A period of 2 to 4 months was allowed for recuperation between topical treatment and surgery. All patients had a 10-mm long fusiform biopsy taken as a negative control to establish a baseline MDC. The negative control was sampled from an ipsilateral site showing similar actinic changes as did the LM site. The mean distance of the negative control was 6 cm from the LM site. Frozen sections were prepared on radially sectioned LM specimens and stained with hematoxylin and eosin, Mart-1 (Cell Marque A103), and SOX10 (BioCare Medical BC34). The LM sites were located on the head (n = 47), neck (n = 3), and upper extremities (n = 2). Each resected LM lesion was quadrisected. The MDCs were simultaneously counted by the authors (S.F. and G.B.) viewing the specimens under a light microscope at 400 × magnification at 3 sites per quadrant and independently recorded. The MDCs for the negative control and all 4 quadrants of the resected LM were then averaged and compared.
Results
A total of 52 specimens were assessed. (13 women and 39 men; mean age, 67 years). The median (SD) MDC from the negative controls was 20.0 (6.2) (range, 9.0-36.7). The median (SD) MDC from the postimiquimod treatment sites was 14.4 (5.4) (range, 0.5-26.6). Using the 2-tailed paired t test, the results showed statistical significance (P < .001) (Figure) (Table). Of 52 participants, 44 (85%) showed decreased MDCs compared with the negative control group. Residual LM was observed in the central areas of 9 (17%) specimens, whereas 43 (83%) had no residual LM. One specimen had an averaged count of 0.5 MDC per 400 × magnification on all 4 quadrants of the specimen compared with a 32.4 MDC on the negative control specimen (0.02:1). Positive controls to verify Mart-1 and SOX10 immunostaining were used in all cases.
Figure. Effect of Topical 5% Imiquimod Cream on Melanocyte Density Counts.
LM indicates lentigo maligna. The data shown is the melanocyte density count (MDC) per 400 × magnification in 52 participants with LM treated with neoadjuvant topical imiquimod 5% cream compared with negative controls. A total of 44 of 52 cases showed a decrease in MDC after 5% topical imiquimod treatment compared with the control biopsy specimens.
Table. Statistical Summary of Study Data for 52 Cases of LM Treated With Neoadjuvant Topical Imiquimod 5% Cream Compared With Concomitant Negative Controls.
| Variable | Mean (SD) | Median (Range) | 2-Tailed Paired t Test |
|---|---|---|---|
| Negative control, melanocytes per 400 × magnification |
20.0 (6.2) | 20.3 (9.0-36.7) | P < .001 |
| LM, melanocytes per 400 × magnification |
14.4 (5.4) | 13.9 (0.5-26.6) |
Abbreviation: LM, lentigo maligna.
Discussion
Neoadjuvant topical imiquimod 5% cream applied 5 times weekly for 8 weeks was associated with decreased MDCs in LM treatment sites compared with the MDCs of negative control sites. The decreased melanocytic hyperplasia in imiquimod-treated sites reduced ambiguity in making a distinction between the border of the excised LM and background melanocytic hyperplasia.
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