Ki-67 expression is superior to mitotic count and novel proliferation markers PHH3, MCM4 and mitosin as a prognostic factor in thick cutaneous melanoma

Abstract

Background: Tumor cell proliferation is a predictor of survival in cutaneous melanoma. The aim of the present study was to evaluate the prognostic impact of mitotic count, Ki-67 expression and novel proliferation markers phosphohistone H3 (PHH3), minichromosome maintenance protein 4 (MCM4) and mitosin, and to compare the results with histopathological variables.

Methods: 202 consecutive cases of nodular cutaneous melanoma were initially included. Mitotic count (mitosis per mm2) was assessed on H&E sections, and Ki-67 expression was estimated by immunohistochemistry on standard sections. PHH3, MCM4 and mitosin were examined by staining of tissue microarrays (TMA) sections.

Results: Increased mitotic count and elevated Ki-67 expression were strongly associated with increased tumor thickness, presence of ulceration and tumor necrosis. Furthermore, high mitotic count and elevated Ki-67 expression were also associated with Clark's level of invasion and presence of vascular invasion. High expression of PHH3 and MCM4 was correlated with high mitotic count, elevated Ki-67 expression and tumor ulceration, and increased PHH3 frequencies were associated with tumor thickness and presence of tumor necrosis. Univariate analyses showed a worse outcome in cases with elevated Ki-67 expression and high mitotic count, whereas PHH3, MCM4 and mitosin were not significant. Tumor cell proliferation by Ki-67 had significant prognostic impact by multivariate analysis.

Conclusions: Ki-67 was a stronger and more robust prognostic indicator than mitotic count in this series of nodular melanoma. PHH3, MCM4 and mitosin did not predict patient survival.

Figure 1

Immunohistochemical staining showing PHH3 positive prophases and mitotic figures (A and B), high expression of MCM4 (C) and mitosin (D).

Figure 2

Scatter plots with regression lines illustrating the relationships between mitotic count (mitosis/mm²), Ki-67 expression and PHH3 expression.

Figure 3

Survival curves according to the Kaplan-Meier method with cut-off points at the lower quartile for mitotic count (<1.7 mitotic figures/mm²), Ki-67 expression (≤16% positive tumor cell nuclei) and mitosin (SI ≤ 6), and at the median values for PHH3 (≤0.8% positive nuclei) and MCM4 (≤40.7% positive nuclei).