Activation of the extracellular signal regulated kinase (ERK) pathway in human melanoma

Abstract

Background: Several studies suggest that melanoma may be resistant to treatment because of resistance to apoptosis and that this may be the result of activation of the extracellular signal regulated kinase (ERK1/2) pathway.

Aims: To test this hypothesis by examining the expression of ERK1/2 and its activated form in histological sections of melanoma and its relation to known prognostic features of the disease.

Materials/methods: Immunohistochemistry with antibodies to ERK1/2 and phosphorylated ERK (p-ERK) was performed on formalin fixed sections from 42 primary melanomas, 38 metastases, and 20 naevi. Fourteen of the primary melanomas were in the radial and 28 in the vertical growth phase.

Results: ERK1/2 was widely expressed (100%) in all the (pigmented) lesions studied. p-ERK1/2 expression was much lower in compound (32.4%) and dysplastic (54.5%) naevi than in primary melanoma (nodular 78.8%, superficial spreading 67%) and subcutaneous metastases (76.3%). p-ERK expression was much lower in lymph node metastases (48.5%), suggesting that the microenvironment may influence the activation of ERK. There was a (non-significant) trend for p-ERK expression to be higher in thick (>1.0 mm) versus thin (< or =1.0 mm) melanoma (p = 0.23). There was a trend for overall survival to be related to p-ERK expression in patients with melanoma over 1 mm in thickness.

Conclusions: Expression of activated ERK1/2 in melanocytic lesions appears to be related to malignant potential so that activation of ERK1/2 may be important in melanoma progression. These results provide important histological support for the proposal that inhibition of this signalling pathway may be useful in treatment of melanoma.

Figure 1

Extracellular signal regulated kinase 1/2 expression in different types of primary and secondary melanocytic tumours. (A) Compound naevus; positive cells, 80%; immunoreactive score (IRS), 16; original magnification, ×100. (B) Dysplastic naevus; positive cells, 100%; IRS, 20; original magnification, ×200. (C) Melanoma ⩽1.0 mm; positive cells, 100%; IRS, 30; original magnification, ×200. (D) Melanoma >1.0 mm; positive cells, 98%; IRS, 19.6; original magnification, ×100. (E) Desmoplastic melanoma; positive cells, 90%; IRS, 18; original magnification, ×200. (F) Metastatic melanoma: (1) subcutaneous metastasis; positive cells, 100%; IRS, 30; original magnification, ×100; (2) lymph node metastasis; positive cells, 85%; IRS, 12.8; original magnification, ×100. (G) Normal skin melanocytes; positive cells, < 2%; IRS, < 2 (arrow); original magnification, ×400.

Figure 2

Mean percentage of cells positive for activated extracellular signal regulated kinase (p-ERK) in different types of melanocytic lesions. CN, compound naevus; DN, dysplastic naevus melanoma; LNMM, lymph node metastatic melanoma; M, melanoma; SMM, subcutaneous metastatic melanoma; thick, > 1.0 mm; thin, ⩽ 1.0 mm. The Y bar indicates one standard error. *CN v thick M, p < 0.0001 (Tukey-Kramer); CN v SMM, p < 0.001 (Tukey-Kramer); **thick M v LNMM, p < 0.005.

Figure 3

Activated extracellular signal regulated kinase (p-ERK) expression in different types of primary and secondary melanocytic tumours. (A) Compound naevus: (1) p-ERK(+); positive cells, 95%; immunoreactive score (IRS), 9.5; original magnification, ×100; (2) p-ERK(−); original magnification, ×200. (B) Dysplastic naevus; positive cells, 50%; IRS, 5; original magnification, ×200. (C) Melanoma ⩽1.0 mm; positive cells, 97%; IRS, 19.4; original magnification, ×200. (D) Melanoma >1.0 mm; positive cells, 98%; IRS, 24.5; original magnification, ×100. (E) Desmoplastic melanoma; positive cells, 70%; IRS, 7; original magnification, ×200. (F) Metastatic melanoma: (1) subcutaneous metastasis; positive cells, 98%; IRS, 19.6; original magnification, ×200; (2) lymph node metastasis, p-ERK(+); positive cells, 90%; IRS, 18; original magnification, ×200; (3) lymph node metastasis, p-ERK(−); original magnification, ×200. (G) Normal skin melanocytes; p-ERK(−); original magnification, ×400.

Figure 4

Mean percentage of cells positive for extracellular signal regulated kinase 1/2 (ERK1/2) and p-activated ERK1/2 (p-ERK) in naevi and different histopathological types of primary melanoma. AL, acral lentiginous; CN, compound naevus; DM, desmoplastic melanoma; DN, dysplastic naevus; NM, nodular melanoma; SSM, superficial spreading melanoma. *NM v CN, p < 0.0005 (Tukey-Kramer); NM v SSM, p =  0.27 (Tukey-Kramer).

Figure 5

Percentage of activated extracellular signal regulated kinase (p-ERK) positive tumour cells in primary melanoma correlated with tumour thickness. There was a trend towards increased p-ERK expression with increased tumour thickness, although this was not significant (R² = 0.0454, p = 0.17).

Figure 6

Kaplan–Meier estimates of overall survival (OS) after excision of primary cutaneous melanoma. (A) OS of patients with melanoma ⩽ 1 mm thickness versus > 1 mm thickness. (B) OS of patients with thick melanoma having % activated extracellular signal regulated kinase (p-ERK) below the median value (⩽ 80%) versus patients with values above the median (> 80%).