Cytokeratin expression in malignant melanoma: potential application of in-situ hybridization analysis of mRNA

Abstract

Occasional reports indicated cytokeratin (CK) protein expression (mainly by immunohistochemistry) in malignant melanoma (MM) and suggested an association with unfavorable clinical parameters. However, the mRNA expression of CK and its clinicopathologic significance in MM has not been specifically evaluated. We investigated the mRNA and protein expression of nine CKs in melanoma cell lines and tissues, in particular the prognostic significance of CK18 mRNA expression. Reverse transcription (RT)-PCR (CK6-10, 14 and 18-20), in-situ hybridization (ISH) (CK18), and western blotting (CK18 and pan-cytokeratin AE1/AE3) were performed on MM cell lines A375, A875, M14, and SK-MEL-1. Eighty MM tissue samples were analyzed by ISH and immunohistochemistry for CK18 expression. The mRNA of CK6-8, 10, 14, 18, and 19 (but not CK9 and 20) was detected in one to four of the melanoma cell lines by RT-PCR. CK18 was detected in all four cell lines by RT-PCR, ISH, and western blotting. CK18 mRNA ISH was positive in three of 30 (10.0%), 10 of 25 (40.0%), and 12 of 25 (48.0%) of primary cutaneous, primary mucosal, and metastatic melanomas, respectively (overall positivity: 25 of 80, 31.3%). CK18 immunostaining was only observed focally in eight of 80 (10.0%) of MM tissue samples, and AE1/AE3 immunostaining was altogether negative. Significantly, CK18 mRNA ISH positivity (but not protein immunohistochemistry) was associated with poorer prognosis by both univariate analysis (P<0.001) and multivariate analysis (relative risk=5.430, 95% confidence interval 2.246-13.128, P<0.001). CK18 mRNA could be identified in one-third of melanoma tissue samples and is an adverse prognostic factor. ISH is superior to immunohistochemistry for analyzing CK18 expression in MM.

Metastatic Melanoma With Striking Adenocarcinomatous Differentiation Illustrating Phenotypic Plasticity in Melanoma

“…Cytokeratin expression in melanoma has been reported previously, 5,10,28 but usually involves simple keratins; the expression of CK20, as was found in this case, is distinctly unusual in melanoma. In a series of melanoma cell lines and tissues analyzed for mRNA and protein expression of a panel of cytokeratins, none was found to express CK20.…”

“…In a series of melanoma cell lines and tissues analyzed for mRNA and protein expression of a panel of cytokeratins, none was found to express CK20. 10 Wen et al recently reported a 27-year-old woman with a primary, non-pigmented right scalp melanoma containing intimately admixed glandular elements. 33 The melanoma component of that tumor stained for classic melanocyte markers (S100, HMB-45, MiTF-1, and PNL2), whereas the carcinomatous component was positive for cytokeratins AE1/AE3 and Cam5.2, as well as MiTF-1, suggesting true transdifferentiation of melanoma into carcinoma, however, no genetic analysis was performed to prove a clonal relationship.…”

“…Banerjee and Eyden have defined this phenomenon in melanomas as the development of morphologically, immunohistochemically, and/or ultrastructurally recognizable non-melanocytic cell or tissue components within an existing melanoma. 4 The wide-ranging types of divergent differentiation reported in melanomas include fibroblastic/myofibroblastic, schwannian, smooth muscle, rhabdomyosarcomatous, osteocartilaginous, ganglionic and ganglioneuroblastic, and neuroendocrine, 1–4,6,10,17,19,20,26 as well as rare reports of epithelial differentiation. 4,14,25,33 …”

Aberrant intermediate filament and synaptophysin expression is a frequent event in malignant melanoma: an immunohistochemical study of 73 cases

“…1 Welldescribed examples of this phenomenon include keratin expression in angiosarcoma, 2 leiomyosarcoma, 3 and Ewing sarcoma, 4 and synaptophysin expression in alveolar rhabdomyosarcoma. 5 It is less widely appreciated that melanomas too may show aberrant expression of various immunohistochemical markers, with a relatively small number of reports, of melanomas showing expression of intermediate filaments other than vimentin (e.g., keratins, desmin, neurofilament protein, and glial fibrillary acidic protein) [6][7][8] and/or neuroendocrine markers. [9][10][11] Over the past several years, we have seen in consultation a significant number of melanomas in which aberrant expression of intermediate filaments and/or neuroendocrine markers obscured the correct diagnosis, and prompted consideration of various non-melanocytic neoplasms, including carcinoma, rhabdomyosarcoma, neural neoplasms, and various neuroendocrine tumors.…”

Melanoma circulating tumor cells: Benefits and challenges required for clinical application

“…Spiking experiments showed a !60% recovery rate of 4, 20, 100 and 500 spiked SkMel28 cells when assessed by qPCR amplification of cytokeratin 8 (KRT8) and 18 (KRT18) RNA. The SkMel28 cell line strongly expresses these intermediate filament proteins and KRT18 expression has been previously identified as an adverse prognostic factor in melanoma [8].…”