Tyrosinase a useful marker for identifying pagetoid invasion in malignant melanoma

Tyrosinase a useful marker for identifying pagetoid invasion in malignant melanoma

Summary

The presence of melanoma cells within the superficial layers of the epidermis is not always easy to interpret on H&E, immunohistochemical (IHC) stains being necessary. We studied 23 cases of thin malignant melanoma. We compared the amount of pagetoid growth in consecutive slides stained with H&E, S100 protein, HMB45, tyrosinase and TRP2 based a semiquantitative score. Statistical analysis was performed (P<0.05). The extent of pagetoid invasion revealed by S100 protein and H&E was similar. HMB45 showed slightly more numerous intraepidermal invasive cells than H&E. TRP2 had better results than HMB45. Tyrosinase highlighted statistically significant more pagetoid spreading cells comparing both with HMB45 and H&E. Tyrosinase is a useful marker for pagetoid invasion comparing with other IHC markers or H&E.

Introduction

In most of the cases, malignant melanoma (MM) is diagnosed based on hematoxilin-eozin (H&E) appearance, supplemental investigations being performed in a minority of cases. We address our study to differentiation between particular types of nevocellular naevi (predominantly junctional, lentiginous or displastic) and MM. In these cases, one of the clues of differentiation is the presence of melanoma cells within the superficial layers of the epidermis (pagetoid growth). This feature is not always easy to interpret on H&E, immunohistochemical stains being necessary (4,8).

Materials and Methods

We studied 23 cases of thin MM (nontumorigenic MM with Breslow score less than 1mm). We analyzed the presence of pagetoid growth in consecutive slides stained with H&E, S100 protein, HMB45, tyrosinase and TRP2. All the antibodies were incubated with the slides for 1 hour; S100 protein, HMB45 and Melan A were ready-to-use antibodies; for tyrosinase and TRP2 1:2000 dilutions were used. No pretreatment was used for S100 protein. For HMB45, Melan A, 15 min microwave pretreatment in pH 6 citrate buffer was performed; for tyrosinase and TRP2 10 min microwave pretreatment in pH 8 EDTA buffer was used.

The number of the invading melanoma cells was counted in each high power field, the highest figure being attributed as numeric score for each slide. For each case, the smallest number was arbitrarily labeled as 1, the next one 2 and the highest score 5. The scores recorded in immunohistochemical stains were compared with those recorded in H&E for the same case. Statistical analysis was performed using EXCEL and EPIINFO programs (level of statistical significance P<0.05).

Results

The presence of epidermal invasive melanoma cells was noticed in all but 3 cases in H&E stains (fig 1: Epidermal invasion by melanomatous cells. HE x200). The extent of pagetoid invasion revealed by S100 protein and H&E was similar (fig 2: S100 positive cells with pagetoid intraepidermal growth. S100 x200). HMB45 was intense positive in all the cases with slightly more numerous intraepidermal invasive cells comparing with H&E (fig 3: Small groups of positive cells with intraepidermal growth. HMB45 x100). TRP2 showed slightly more numerous cells in pagetoid growth than HMB45 but not significant comparing with H&E (fig 4: Several positive cells with pagetoid intraepidermal growth. TRP2 x200). Tyrosinase highlighted most numerous pagetoid spreading cells, the differences being statistically significant (P<0.05) comparing both with HMB45 and H&E (fig 5: Epidermal invasion by numerous melanomatous cells. Tyr x100; fig 6: Small groups of positive cells with intraepidermal growth. Tyr x400).

Discussions

Lentiginous melanocytic proliferations, especially those with mild cellular atypia, are very difficult to diagnose. The presence of an ascending intraepidermal component is a warning sign balancing the diagnosis towards malignancy (except the dysplastic nevus of genital or mammary location, when pagetoid growth is more prominent). However, especially in small lesions / biopsies, confusions may occur in labeling a lesion as dysplastic nevus (Clark nevus), atypical junctional nevus, melanoma in situ, or even microinvasive MM (2,4,8). Lesions labeled as lentiginous nevi should present accentuation of the rete ridges with small nests of melanocytes at the their tips, while atypical lentiginous nevi associate the presence of cytonuclear atypia to a lentiginous growth of the melanocytes. In both of these situations, there is no pagetoid spread of atypical melanocytes, or if it exists, the pagetoid growth is occasional, in limited areas of the lesions. MM, either in situ or microinvasive, present more abundant pagetoid spread (3,7). Unfortunately, the superficial intraepidermal growth is not readily identifiable on the H&E stained sections. In those cases, IHC tests should be performed in order to establish the presence and the extent of the pagetoid growth. S100 protein, HMB45, melan A, Mitf are consecrated markers but, as our results showed, tyrosinase and, to lesser extend TRP2 may be used in routine diagnosis with successful results (1,5,6).

Conclusions

Tyrosinase is a useful marker for pagetoid invasion comparing with other immunohistochemical markers or H&E, helping in differentiating MM form naevi with prominent intraepidermal compartment.

Supported by National Authority for Scientifical Research, Excellence Research Program, 2006-2008

References

Banerjee SS, Harris M. Morphological and imunohisto-phenotypic variations in malignant melanoma. Histopathology 2000;36:387-402.

Davis T, Zembowicz A Histological evolution of lentiginous melanoma: a report of five new cases. J Cutan Pathol. 2007;34:296-300.

King R, Page RN, Googe PB, Mihm MC Jr Lentiginous melanoma: a histologic pattern of melanoma to be distinguished from lentiginous nevus. Mod Pathol. 2005;18:1397-401.

Massi G Melanocytic nevi simulant of melanoma with medicolegal relevance. Virchows Arch. 2007;451:623-47

Miettinen M, Fernandez M, Franssila K, Gatalica Z, Lasota J, Sarlomo-Rikala M. Microphthalmia transcription factor in the immunohistochemical diagnosis of metastatic melanoma: comparison with four other melanoma markers. Am J Surg Pathol 2001;25:205-211.

Slominski A, Coming of Age of Melanogenesis-Related Proteins. Arch Pathol Lab Med 2002;126:775-777

Tannous ZS, Lerner LH, Duncan LM, Mihm MC Jr, Flotte TJ Progression to invasive melanoma from malignant melanoma in situ, lentigo maligna type. Hum Pathol. 2000;31:705-8.

Wick MR, Patterson JW Cutaneous melanocytic lesions: selected problem areas. Am J Clin Pathol. 2005;124 Suppl:S52-83