MOC-31, Cytokeratin 7 and S-1 00 Protein Immunoreactivity in Merkel Cell and Merkel Cell Carcinoma

T. Garcia-Caballero1, E. Pintos2, R. Gallego1, C. Parrado3, M. Blanco1, U.G.

Falkmer5, S. Falkmer4, J. Forteza2, and A. Beiras1

1 Department of Morphological Sciences, University of Santiago de Compostela, Spain

2nepartment of Pathology, University of Santiago de Compostela, Spain

3Department of Histology and Pathology, University of Malaga, Spain

4Laboratory of Pathology and Clinical Cytology, Sant Olav's University Hospital., Trondheim, Norway

5cancer Clinic, Sant Olav's University Hospital., Trondheim, Norway

Summary

The histological diagnosis of Merkel cell carcinoma can be difficult because it looks like other small blue cell tumors. In addition to the expected immunohisto­chemical results, some authors have reported reactivity for S-1 00 protein and CK 7 in Merkel cell carcinomas. The aim of the present work was to provide addi­tional information about these unexpected immunoreactivities as well as to test the monoclonal antibody MOC-31 that was not previously described in Merkel cells or Merkel cell carcinomas. Nineteen cases of Merkel cell carcinoma were studied. MOC-31 plasma membrane immunoreactivity was found in 12 of 19 cases studied (63.1%). Immunoreactivity for CK 7 was observed in two cases (10.5%). S-100 protein was positive in four cases (21 %). Normal human skin showed immu­nostaining for MOC-31 in the plasma membrane of virtually all Merkel cells. These cells were also immunoreactive for CK 7. S-1 00 protein was negative in human Merkel cells, but intensely positive in pig snout Merkel cells. In conclu­sion, normal human Merkel cells showed MOC-31 and CK 7 immunostaining and positivity for MOC-31, CK 7, and S-100 protein do not exclude the diagnosis of Merkel cell carcinoma.

K. I. Baumann et al. (eds.), The Merkel Cell© Springer-Verlag Berlin Heidelberg 2003

232 Garcia-Caballero et al.

Introduction

The histological diagnosis of Merkel cell carcinoma can be difficult because it looks like other small blue cell tumors. Immunohistochemical positivity for cy­tokeratin (CK) 20, neuroendocrine markers and neurofilaments confirm the diag­nosis. In addition to these markers, some authors have reported reactivity for S-100 protein (Voigt et al. 1985; Drijkoningen et al. 1986; Heenan et al. 1990; Skoog et al. 1990; Kontochristopoulos et al. 2000) and CK 7 (Jensen et al. 2000) in Merkel cell carcinomas. The aim of the present work was to provide additional information about these unexpected immunoreactivities as well as to test the monoclonal antibody MOC-31 in normal Merkel cells and Merkel cell carcino­mas. This antibody recognises the human pancarcinoma-associated epithelial gly­coprotein-2 (EGP-2), also known as Ep-CAM, a 38-kDa transmembrane glycopro­tein. MOC-31 has been assigned to the SCLC (small cell lung cancer)-cluster 2 of antibodies (Souhami et al. 1991) and it was demonstrated to be also useful in the differential diagnosis between adenocarcinoma and mesothelioma (Edwards and Oates 1995; Sosolik et al. 1997; Ordonez 1998), but to our knowledge it was not previously described in Merkel cells or Merkel cell carcinomas.

Materials and Methods

Nineteen cases of Merkel cell carcinoma were obtained from the files of the Clinical University Hospital of Santiago de Compostela, Spain (9 cases) and the Department of Oncology and Pathology, Karolinska Hospital, Stockholm, Sweden (10 cases). Thirteen patients were female and six male, and patient age ranged from 20 to 93 (mean, 70.6 years). The most common localization was extremities (n=9) and head (n=8). Immunohistochemistry for CK 20 (Dako), chromogranin (Biogenex), MOC-31 (Dako), CK 7 (Dako) and S-100 protein (Dako) was auto­matically performed (TechMate 500) using the DAKO Envision staining proce­dure and diaminobenzidine as chromogen.

Results

By immunohistochemical techniques all tumors but three were positive for CK 20 and all cases but one were positive for chromogranin. MOC-31 plasma mem­brane immunoreactivity was found in 12 of 19 cases studied (63.1 %). Most of them showed a diffuse pattern, but local immunoreactivity was also found (Fig. 1A, B). Immunoreactivity for CK 7 was observed in two cases (10.5%). One of them showed small and pleomorphic giant cells, both cell types being positive for CK 7 and CK 20 (Fig. 2A, B). S-100 protein was positive in four cases (21%) with nuclear and cytoplasmic immunostaining (Fig. 3A, B).

MOC-31, CK 7 and S-100 in Merkel cell and Merkel cell carcinoma 233

Fig. lA-C. MOC-31. A Merkel cell carcinomas showed diffuse (left) or focal (right) immunoreactivity for MOC-31 (x10). BAt higher magnification it was demonstrated that MOC-31 presented plasma membrane immunostaining (left), whereas CK 20 showed a dot­like pattern (right) (x60). C Normal Merkel cells of human fingertip also displayed MOC-31 immunoreactivity in the plasma membrane (x100)

Fig. 2A-C. CK 7. A, B Case of Merkel cell carcinoma positive for CK 7 (A) and CK 20 (B). Immunoreactivity was found in both small cells and giant pleomorphic cells (x40). C Normal human Merkel cells (arrowheads) were positive for CK 7 (left), but the intensity of immunostaining was weaker than for CK 20 (right) (x60)

Fig. 3A-C. S-100 PROTEIN. A Serial sections of a Merkel cell carcinoma showing immunoreactivity for S-1 00 protein (left) and CK 20 (right) (xI 0). B Higher magnification evidenced a nuclear and cytoplasmic positivity for S-100 protein (x40). C Intense immu­nostaining for S-1 00 protein was found in pig snout skin Merkel cells situated in both epi­dermis (left) and vibrissae (right) (x40)

The same markers were studied in normal Merkel cells of human fingertip and pig snout skin. Normal human skin showed immunostaining for MOC-31 in the plasma membrane of virtually all Merkel cells (Fig. 1 C). These cells were also immunoreactive for CK 7, although with lower intensity than for CK 20 (Fig. 2C). S-1 00 protein was negative in human Merkel cells, but intensely positive in pig snout Merkel cells, with nuclear and cytoplasmic positivity (Fig. 3C).

234 Garcia-Caballero et al.

Discussion

To our knowledge, MOC-31 immunoreactivity has not previously been de­scribed in normal Merkel cells or Merkel cell carcinomas. However, MOC-31 positivity was found in most carcinomas and is frequently used in the immunohis­tochemical battery for small cell carcinomas; it has also been proposed for radio­immunodetection and immunotherapy of these tumors (Myklebust et al. 1993; Kosterink et al. 1995; McLaughlin et al. 1999). The finding ofMOC-31 in Merkel cell carcinomas excludes the use of this marker in the differential diagnosis with cutaneous metastases of small cell lung carcinomas. The clinical significance of MOC-31 expression in Merkel cell carcinomas remains to be studied in larger se­nes.

Marked expression of CK 20 without concomitant CK 7 was assumed to be typical for both colorectal adenocarcinoma and Merkel cell carcinoma, and CK 7, which identifies bronchial small-cell carcinoma, is normally used for the differen­tial diagnosis with Merkel cell carcinoma (Goessling et al. 2002). Our finding of CK 7 in occasional Merkel cell carcinomas confirms the results reported by Jensen et al. (2000). Normal Merkel cells also showed CK 7 immunoreactivity. This re­sult agrees with a previous paper by Lundquist et al. (1999). These authors re­ported that Merkel cells express CK 7 with lower frequency than CK 20. How­ever, we found that virtually all Merkel cells were positive for CK 7, although some of them showed very weak immunostaining. The lower frequency reported could be explained assuming that Merkel cells express CK 7 in smaller quantities than CK 20. The sensitivity of the immunohistochemical technique may not al­ways be sufficient to detect all Merkel cells by CK 7.

In cutaneous pathology, S-1 00 protein is primarily used as a marker for the di­agnosis of malignant melanoma. However, we showed occasional immunoreactiv­ity for S-1 00 in Merkel cell carcinomas as was previously described by several au­thors (Voigt et al. 1985; Drijkoningen et al. 1986; Heenan et al. 1990; Skoog et al. 1990; Kontochristopoulos et al. 2000). S-100 protein expression in normal Merkel cells shows important differences between species. We found S-100 protein im­munoreactivity in Merkel cells of pig snout skin, as previously described by Hartschuh and Weihe (1988). However, we did not find immunostaining for S-100 protein in human Merkel cells and the same result was reported by Moll et al. (1996) in rodents.

In conclusion, (1) normal human Merkel cells showed MOC-31, CK 7 immu­nostaining and S-1 00 protein was only found in pig snout Merkel cells, and (2) positivity for MOC-31, CK 7 and S-100 protein does not exclude the diagnosis of Merkel cell carcinoma.

MOC-31, CK 7 and S-100 in Merkel cell and Merkel cell carcinoma 235

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