Growth rate of melanoma in vivo and correlation with dermatoscopic and dermatopathologic findings

Abstract

Objectives: The aim of this study was to calculate the horizontal growth rate of melanoma in vivo and to correlate it with morphologic findings.

Patients and methods: We searched our database for melanomas for which sequential dermatoscopic images and histopathologic slides were available. The final sample consisted of 50 melanomas of 48 patients (mean age: 50 ± 15 years, 62% females). We calculated the horizontal growth rate in mm(2) per year by morphometric analysis of digital dermatoscopic images. Dermatoscopic and dermatopathologic findings were assessed according to predefined criteria and correlated with the horizontal growth rate.

Results: The median time interval between baseline and follow-up image was 12 months (range: 2-100 months). The majority of melanomas were in situ (n=28, 56%). The mean horizontal growth rate of all melanomas was 5.3 mm(2)/year (SD: ± 5.8 mm(2)/year). The histopathologic findings of numerous and large epidermal nests were associated with rapid growth. This histopathologic pattern corresponded to a pattern of clods ("globules") dermatoscopically. From a dermatoscopic point of view, melanomas with a main pattern of clods grew significantly faster (mean horizontal growth rate: 10.4 mm(2)/year, 95% CI: 6.4-14.4 mm(2)/year) than melanomas with mainly a reticular pattern (4.8 mm(2)/year, 95% CI: 2.7-7.0 mm(2)/year) or with other patterns (2.6 mm(2)/year, 95% CI: -0.5-5.6 mm(2)/ year, p=0.01).

Conclusion: Morphologic characteristics of melanoma are associated with biologic behavior. Large and numerous epidermal nests (corresponding to a pattern of clods dermatoscopically) indicate more rapid growth.

Keywords: dermotoscopy; horizontal growth rate; melanoma in vivo.

Figure 1.

Schematic drawing of scoring of nesting. A: intraepidermal melanocytes present almost exclusively as single cells with only rare nests (score=0); B: intraepidermal melanocytes predominantly arranged as single cells with no more than 25% of cells in nests (score=1); C: 25%–50% of the intraepidermal melanocytes in nests (score=2); D: >50% of the intraepidermal melanocytes in nests (score=3).

Figure 2.

Sequential dermatoscopic images of a melanoma with a pattern of clods. (A) Baseline image; (B) follow up image. The baseline image was taken 5.1 months before the follow-up image. The size at baseline was 32.6 mm² and after follow-up 38.9 mm2. The increase in size was 6.3 mm², which corresponds to a horizontal growth rate of 1.1 mm² per month.

Figure 3.

Micrographs of the melanoma shown in Figure 2. The neoplastic melanocytes in the epidermis are mainly arranged in nests. More than 50% of these nests are large.

Figure 4.

Sequential dermatoscopic images of a melanoma with a reticular pattern. (A) Baseline image; (B) follow up image. The baseline image was taken 35.4 months before the follow-up image. The size at baseline was 12.6 mm² and after follow-up 18.8 mm². The increase in size was 6.2mm², which corresponds to a horizontal growth rate of 0.2 mm² per month.

Figure 5.

Micrographs of the melanoma shown in Figure 4. The neoplastic melanocytes in the epidermis are mainly arranged as single cells.

Figure 6.

Horizontal growth rate by dermatoscopic pattern: The growth rate was highest for melanomas with a pattern of clods (P for difference: 0.012).

Figure 7.

Horizontal growth rate by dermatopathologic findings. The scores for scatter (p=0.035), nesting (p=0.009), nest size (p=0.012), and cell size (p=0.048) were significantly associated with the horizontal growth rate. All p-values are derived from analysis of variance (ANOVA).