Alterations in cadherin and catenin expression during the biological progression of melanocytic tumours.

AIMS: Compelling evidence from cell culture studies implicates cadherins in the neoplastic progression of melanocytic tumours but few reports describe the expression of cadherins and the related transmembrane proteins, catenins, in a full range of benign and malignant excised melanocytic tumours. METHODS: Using immunohistochemistry and western blotting after tissue fractionation, the pattern of expression of cadherins/catenins was studied in a range of surgically excised melanocytic tumours, from dysplastic naevi to stage III cutaneous metastatic malignant melanoma. RESULTS: Appropriate membranous expression of E-cadherins and P-cadherins is seen in dysplastic naevocytes with an epithelioid phenotype and is largely maintained with malignant transformation to radial growth phase melanoma and primary vertical growth phase malignant melanoma. Loss of membranous E-cadherin is seen in a small number of vertical growth phase melanomas only when metastasis has occurred. However, there is a concomitant dramatic loss of membranous P-cadherin expression in all melanomas at the same stage. A minority of metastatic melanomas show de novo membranous N-cadherin expression in comparison with dysplastic naevi and primary melanoma. Membranous expression of the desmosomal cadherin, desmoglein, was not seen in any tumour studied. Frequently, beta catenin is aberrantly produced in the cytoplasm of cells in dysplastic naevi and metastatic malignant melanoma, with an implied compromise to adhesive function. Furthermore, membranous gamma catenin expression was not seen in any of the 70 melanocytic tumours studied, implying obligatory transmembrane binding of cadherins to beta catenin for maintenance of adhesive function. CONCLUSIONS: The most important alterations in membranous cadherin and catenin expression are seen late in the biological progression of melanocytic tumours at the stage of "in transit" or regional lymph node metastasis, with implications for tumour growth, invasion, and dissemination.     

CADHERIN EXPRESSION IN MELANOCYTIC NAEVI AND MALIGNANT MELANOMAS

An immunocytochemical study has been undertaken of cadherin expression in 11 benign melanocytic naevi and 14 malignant melanomas. Anti-pan-cadherin rabbit antibodies, which recognize multiple cadherin subtypes, demonstrated cadherin expression of moderate or strong intensity in 8 of 11 naevi. Expression was restricted to the more superficial melanocytes which possessed abundant cytoplasm (type A melanocytes). More deeply located melanocytes possessing little cytoplasm (type B melanocytes) or having a spindle cell morphology (type C melanocytes) lacked detectable pan-cadherin expression. The monoclonal antibody HECD-1 detected weak E-cadherin immunostaining in all 11 naevi, expression again being limited, with a single exception, to type A melanocytes. Cadherin immunostaining of moderate or strong intensity was detected by the pan-cadherin antibody in all 14 malignant melanomas. In contrast to naevi, cadherin expression in melanomas frequently extended into the deepest portions of the tumours. E-cadherin immunostaining in malignant melanomas was generally much stronger than that seen in naevi, often being of comparable intensity to the pan-cadherin staining. In summary, cadherins are frequently expressed in melanocytic tumours. In naevi, cadherin expression is related to the degree of melanocytic maturation. Cadherin expression, and particularly E-cadherin expression, tends to be greater in malignant melanomas than in naevi.     

E-cadherin/catenin complex in benign and malignant melanocytic lesions

E-cadherin is a calcium-dependent cell-cell adhesion molecule expressed by melanocytes and responsible for their adhesion to keratinocytes in vitro. In this study, the expression of E-cadherin and its associated cytoplasmic proteins alpha-, beta-, and gamma-catenin was evaluated in melanocytic lesions by immunohistochemistry. E-cadherin expression was evaluated in 70 malignant melanomas and the catenins in 35 of these specimens. Twenty benign melanocytic naevi were also evaluated for E-cadherin and catenin expression. In normal epidermis, E-cadherin/catenin immunostaining was localized at the intercellular borders. In melanomas, a differential loss of E-cadherin expression was observed. Membranous E-cadherin staining was absent in dermal nests of melanomas in their radial growth phase and in Clark level II and III lesions, whereas it was present in a high proportion of melanomas in their vertical growth phase, in Clark level IV and V lesions and in metastasizing melanomas. In contrast, superficial compartments of naevi showed membranous E-cadherin immunoreactivity and junctional naevus cell nests displayed heterogeneous or diffuse cytoplasmic staining. Cytoplasmic alpha- and beta-catenin, but not gamma-catenin staining were detected in all benign and malignant lesions. These findings indicate that qualitative changes in the expression and cellular localization of E-cadherin and of alpha-, beta-, and gamma-catenin occur in melanocytic lesions and may reflect different stages in their progression.     

Reduced expression of p16 and p27 is correlated with tumour progression in cutaneous melanoma

AIMS: To determine if the cyclin dependent kinase inhibitors (CDKIs) p16 and p27 show reduced expression in the progression from benign to malignant melanocytic tumours, and to correlate these findings with patient prognosis. METHODS: Ninety-two melanocytic tumours were assessed for immunohistochemical expression of p16 and p27. These specimens included nine compound naevi, 10 dysplastic naevi, 17 thin (<1 mm) melanomas, 22 thick (>1 mm) melanomas, nine in-transit metastases, 13 lymph node metastases, and 12 soft tissue metastases. Clinicopathological information on the 39 patients with melanoma primaries was obtained from the Sydney Melanoma Unit database. The median follow up period was 43.3 months. RESULTS: A significant loss of expression of p16 and p27 was found with tumour progression. Positive expression of p27 was found in all compound and dysplastic naevi but only 43.6% of melanoma primaries. Expression of p27 was greater in lymph node and in-transit metastases (63.6%), but lower in soft tissue metastases (36.4%). Positive expression of nuclear p16 was evident in 73.7% of benign naevi, 28.2% of primary melanomas and 14.7% of metastatic melanomas. Neither p16 nor p27 expression was significantly correlated with overall survival, disease free survival or other clinicopathological markers. CONCLUSIONS: The CDKIs p16 and p27 are associated with tumour progression in melanoma, but do not reliably predict recurrence or survival.     

Nuclear pseudoinclusions in melanocytic naevi and melanomas.

Melanocytes in melanocytic naevi and melanomas can display great variation. The presence of nuclear pseudoinclusions (NPI) is said to be useful in the histological and cytological differential diagnosis of malignant melanoma. The prevalence and characteristics of NPI in a series of 493 naevi and 50 melanomas are described. NPI were found in 31% of adult naevi, 30% of congenital naevi from children, 42% of Spitz naevi, 20% of dysplastic naevi, and 56% of melanomas. The presence of NPI is not a reliable criterion for differentiating melanoma from benign melanocytic lesions, although it is useful in distinguishing melanocytic from non-melanocytic tumours.     

MATRIX METALLOPROTEINASE-2 (72 kD TYPE IV COLLAGENASE) EXPRESSION OCCURS IN THE EARLY STAGE OF HUMAN MELANOCYTIC TUMOUR PROGRESSION AND MAY HAVE PROGNOSTIC VALUE

Matrix metalloproteinase-2 (MMP-2), a member of the matrix metalloproteinase family, participates in degradation of the pericellular and extracellular matrix during neoplastic growth and metastasis. Experimental data have substantiated its role in melanoma invasion, but there is no information at present concerning its expression in histological specimens from human melanocytic tumours. This study describes the occurrence and immunolocalization of MMP-2 in human melanocytic lesions, defining distinct steps in melanoma progression. Paraffin-embedded sections from 118 melanocytic lesions were immunostained using a specific antibody to 72 kD type IV collagenase. The material included 34 common naevocellular naevi, 14 dysplastic naevi, 21 in situ melanomas, 20 primary malignant melanomas, and 29 melanoma metastases. Intracytoplasmic MMP-2 immunoreactive protein was found in the ‘naevocytic nests’ of common naevi, in junctional naevus cells, and in melanoma cells. The surrounding normal skin stained negatively, except for occasional macrophages, sweat glands, and hair follicles. The number of MMP-2-positive cells increased with decreasing architectural organization and increasing atypia in the melanocytic lesions. The MMP-2 positivity in the primary and subcutaneous melanoma lesions correlated with later haematogenous metastasis. The data suggest that MMP-2 expression is an early event in melanocytic tumour progression, but is nevertheless prognostic for haematogenous metastasis in melanoma.     

VS38 immunostaining in melanocytic lesions.

AIMS: To investigate the immunoreactivity of a range of melanocytic lesions, both benign and malignant, with the monoclonal antibody VS38. This was recently described as a marker of reactive/neoplastic plasma cells and, therefore, is useful in the diagnosis of plasmacytoma/myeloma and lymphomas with plasmacytic differentiation. This study was prompted by the recent observation that a plasmacytoid melanoma arising in the nasal cavity was strongly immunoreactive with VS38, which was therefore a potential source of major diagnostic error. METHODS: The Streptavidin-peroxidase complex technique was used on paraffin wax embedded sections of 167 melanocytic lesions. Diaminobenzidine (DAB) was used as chromogen for non-pigmented or lightly pigmented lesions and nickel/DAB for more heavily pigmented lesions. RESULTS: Positive immunostaining for VS38 was seen in 14.5% (10/69) of benign naevi (including 40% (four of 10) of Spitz naevi), 10.5% (two of 19) of dysplastic naevi/in situ melanomas, 92% (35/38) of primary cutaneous melanomas, 100% (four of four) of primary mucosal melanomas, 91.7% (33/36) of recurrent/metastatic melanomas, and 100% (one of one) of clear cell sarcomas of soft tissues. CONCLUSIONS: VS38 immunostaining is frequently positive in primary and recurrent/metastatic malignant melanoma and is also reactive less commonly with benign naevi. These results should be borne in mind when this recently described marker of normal/neoplastic plasma cells is used to identify tumour lineage, particularly in tumours arising at unusual sites, such as in the nasal cavity. The possibility of malignant melanoma should be actively considered and excluded in any undifferentiated tumour which shows VS38 immunoreactivity.     

Inducible nitric oxide synthase expression in benign and malignant cutaneous melanocytic lesions

Nitric oxide (NO) is synthesized by nitric oxide synthases (NOS) and plays an important role in tumour growth. In this study, inducible NOS (iNOS) expression was evaluated by immunohistochemistry in 34 melanocytic naevi (13 common melanocytic naevi, six Spitz naevi, and 15 so-called 'dysplastic naevi'), ten cutaneous melanomas in situ, 50 stage I invasive melanomas, and eight subcutaneous metastases of melanoma. In addition, four samples of melanocytic naevi and four samples of invasive melanomas were collected in order to perform western blot and northern blot analysis. By immunohistochemistry, melanocytic naevi never expressed iNOS. Among cases of melanoma in situ, two were negative, seven displayed staining in less than 20% of melanoma cells, and positivity was observed in 21-50% of melanoma cells in only one case. iNOS expression was detected in 46 out of 50 invasive melanomas (92%). Among these cases, 18 showed positivity in less than 20% of melanoma cells, 18 showed positivity in 21-50% of melanoma cells, and ten showed iNOS expression in more than 50% of cells. Statistical analysis revealed a significant difference in iNOS expression between melanocytic naevi and cutaneous melanomas (p<0.001). In addition, iNOS expression was significantly higher in invasive melanomas than in melanomas in situ (p=0.01). Among primary cutaneous melanomas, no significant correlation was found between iNOS expression and histopathological parameters (histotype, level, thickness and presence of regression/inflammatory infiltrate) and disease-specific survival. In subcutaneous melanoma metastases, iNOS expression was diffuse in more than 50% of cells. Statistical analysis revealed that subcutaneous melanoma metastases showed greater iNOS immunoreactivity than invasive melanomas (p=0.02). Molecular analyses confirmed that iNOS mRNA and protein were highly expressed in melanoma samples. In conclusion, iNOS was constantly absent in melanocytic naevi, whereas it was frequently expressed in melanomas, with up-regulation of the enzyme paralleling tumour progression. These data suggest that iNOS may play a role in the malignant transformation of melanocytes and in tumour growth. In addition, iNOS may be useful as an immunohistochemical marker for malignant melanocytic lesions.     

Expression of interleukin-8 detected by in situ hybridization correlates with worse prognosis in primary cutaneous melanoma

Previous in vitro studies have demonstrated that endogenously produced human interleukin-8 (IL-8) can act as an important growth factor for human melanoma cells in vitro. The present study, has investigated whether IL-8 mRNA expression in primary melanomas may be of prognostic relevance with regard to melanoma progression and metastatic spread. In order to evaluate the clinical significance of IL-8 mRNA expression of melanoma cells in vivo, 59 melanocytic tissue specimens (37 primary melanomas and 22 melanocytic naevi) were studied using a semiquantitative in situ hybridization technique. Significant mRNA expression of IL-8 was found in 59 per cent (22/37) of melanomas. In 19 per cent (7/37) of the malignant melanomas, additional hybridization signals were noted within keratinocytes of the overlying epidermis. In contrast, paralesional normal-appearing epidermis and melanocytes in non-malignant lesions (melanocytic naevi) showed no IL-8 mRNA. Analysis of the relationship between IL-8 expression and clinico-histopathological features showed a significant association between IL-8 mRNA expression and the histological melanoma subtype (IL-8 mRNA: 14/19 in superficial spreading melanoma versus 4/12 in nodular melanoma, p< 0.05). Furthermore, IL-8 expression in primary tumours could be correlated with the patients' clinical course, with time to progression being significantly reduced in primary tumours expressing IL-8 in either the tumour cells or keratinocytes of the overlying epidermis. These results demonstrate for the first time that IL-8 expression, as detected by in situ hybridization in primary tumours, may serve as a significant prognostic factor for tumour progression in human malignant melanoma.     

The approach to the patient with a difficult melanocytic lesion

Although most histological diagnoses are made with relative ease and with great specificity and reproducibility, there is a subset of cases in which a specific and reproducible diagnosis is difficult or even impossible to render. In the melanocytic system, these cases can be divided into two broad categories. The first category, 'superficial atypical melanocytic proliferations of uncertain significance' (SAMPUS), includes predominantly junctional melanocytic proliferations, and melanocytic proliferations that are confined to the epidermis and papillary dermis, without evidence of tumorigenic proliferation or mitotic activity there. The prognosis for cure of these lesions is excellent if they are completely excised. Such lesions may include, for example, dysplastic naevi, Spitz naevi or pigmented spindle cell naevi with a few atypical melanocytes above the dermal-epidermal junction, or with greater than average cytological atypia, or with mitoses, where the differential diagnosis of melanoma in situ is difficult or impossible to rule out. The other category, 'melanocytic tumours of uncertain malignant potential' (MELTUMP), is comprised of melanocytic proliferations that form tumours in the dermis, and are therefore potentially capable of metastasis. Examples of such lesions may include atypical Spitz naevi, deep penetrating naevi, possible naevoid melanomas, or cellular blue naevi, where because of increased mitotic activity or cytologic atypia, a diagnosis of invasive or tumorigenic melanoma cannot be ruled out. In managing such lesions, we follow two main principles. The first is to manage each lesion with therapy designed to be adequate for management of the most significant consideration in the differential diagnosis. The second principle is to make clinicians and patients specifically aware of the diagnostic difficulty in their lesion, so that management can be undertaken on a true informed consent basis.     

IMP-3 is a novel progression marker in malignant melanoma

Insulin-like growth factor-II messenger RNA (mRNA)-binding protein-3 (IMP-3), also known as K homology domain-containing protein overexpressed in cancer (KOC) and L523S, is a member of the insulin-like growth factor-II mRNA-binding protein family and is expressed during embryogenesis and in some malignancies. IMP-3 expression in melanocytic neoplasms has not been investigated. Fifty-six melanocytic neoplasms from 48 subjects were immunohistochemically studied using a monoclonal antibody against L523S/IMP-3. IMP-3 expression in melanoma was significantly higher than in Spitz nevi (P<0.05), and the staining intensity in the Spitz nevi was weak. IMP-3 expression in metastatic melanoma was significantly higher than in primary cutaneous melanoma with a Breslow depth 相似文献   

Versican is differentially expressed in human melanoma and may play a role in tumor development

Undifferentiated human melanoma cell lines produce a large chondroitin sulfate proteoglycan, different from the well-known melanoma-specific proteoglycan mel-PG (Heredia and colleagues, Arch Biochem Biophys, 333: 198-206, 1996). We have identified this proteoglycan as versican and analyzed the expression of versican in several human melanoma cell lines. Versican isoforms are expressed in undifferentiated cell lines but not in differentiated cells, and the isoform expression pattern depends on the degree of cell differentiation. The V0 and V1 isoforms are found on cells with an early degree of differentiation, whereas the V1 isoform is present in cells with an intermediate degree of differentiation. We have also characterized some functional properties of versican on human melanoma cells: the purified proteoglycan stimulates cell growth and inhibits cell adhesion when cells are grown on fibronectin or collagen type I as substrates, and thus may facilitate tumor cell detachment and proliferation. Furthermore, we have analyzed the expression of versican in human melanocytic nevi and melanoma: 10 benign melanocytic nevi, 10 dysplastic nevi, 11 primary malignant melanomas, and 8 metastatic melanomas were tested. Immunoreactivity for versican was negative in benign melanocytic nevi, weakly to strongly positive in dysplastic nevi, and intensely positive in primary malignant melanomas and metastatic melanomas. Our results indicate that versican is involved in the progression of melanomas and may be a reliable marker for clinical diagnosis.     

Determination of proliferating fractions in malignant melanomas by anti-PCNA/cyclin monoclonal antibody

An immunohistochemical study of melanocytic tumours using 19A2, a monoclonal antibody against proliferating cell nuclear antigen (PCNA/cyclin), was performed on tissues routinely processed with formalin fixation and paraffin embedding. In normal skin, keratinocytes of the suprabasal region in epidermis, the papillae and outer root sheath of hair follicles and the basal cells lining the lobules of sebaceous glands were stained in the nucleus. Other skin components, including basal and follicular melanocytes, did not demonstrate nuclear labelling. In addition, expression of PCNA/cyclin in keratinocytes was higher in sun-exposed skin compared with unexposed skin. In melanocytic lesions, PCNA/cyclin positive tumour cells increased in number and staining intensity according to the following progression: common melanocytic naevi; dysplastic naevi; primary melanomas; and metastatic melanomas. Expression of PCNA/cyclin, therefore, provides a useful marker for proliferation and tumour progression in skin.     

A comparative study of proliferation indices and ploidy in dysplastic naevi and malignant melanomas using flow cytometry

Cell proliferation indices and DNA content have been determined in 18 intradermal naevi, 40 dysplastic naevi and 16 superficial malignant melanomas (less than 0.76 mm depth of invasion) using flow cytometry. In this study, proliferation indices of intradermal naevi and dysplastic naevi were not significantly different from each other. Abnormalities of DNA ploidy were not identified in the intradermal naevi or dysplastic naevi; whereas three of the malignant melanomas were aneuploid. In addition, cellular proliferation was increased within the group of malignant melanomas, in comparison with the naevi. This study has found no evidence to indicate that sporadic dysplastic naevi were more likely than intradermal naevi to transform to malignant melanoma, when objective criteria were employed. However, dysplastic naevi could be distinguished from some early malignant melanomas by absence of aneuploidy and by low cell proliferation indices.     

Tetranectin expression in human colonic neoplasia

Pigmented lesions of palmar and plantar skin may cause diagnostic problems, partly because they are infrequently excised and also because some features of benign lesions in these sites may raise the suspicion of melanoma if considered alone. We have examined a series of benign melanocytic lesions and compared them with melanomas from these sites. The presence of severe melanocytic atypia was the most valuable feature in distinguishing between naevi and melanomas. Pagetoid infiltration of the epidermis by single atypical cells, or small groups of cells with abundant pale cytoplasm was seen only in melanomas, while transepidermal elimination of well-circumscribed nests was present only in benign lesions. A lymphocytic infiltrate was present in the dermis in 13 of 14 malignant lesions, but only two of the 26 naevi showed a sparse infiltrate: we suggest that the presence of a lymphocytic infiltrate should prompt a careful search for other features of malignancy. Other features examined, including elongation of rete ridges, pattern of melanocyte distribution at the dermo-epidermal junction, dermal sclerosis, and pigment in the stratum corneum or in the dermis, were seen in both naevi and melanomas and were not found to be useful in distinguishing benign from malignant lesions.     

Cadherins and catenins in pathology

Cell adhesion is a vital process, essential for the establishment and maintenance of tissue architecture and differentiation. Cadherins are a large family of cell adhesion molecules, which mediate cell–cell adhesion via calcium dependent, homotypic interactions. These molecules have intra- and extracellular domains, which are integral to the mechanism of cell adhesion. The intracellular domains interact with catenins, which link the cadherins to the actin cytoskeleton. Alterations in either of these groups of molecules have been identified as key mechanisms in various disease processes. Complex alterations in adhesion have been proposed as a requirement for tumour invasion and metastases. Similar alterations in adhesive properties have been proposed as a mechanism for blistering skin diseases. The literature abounds with evidence, based on molecular studies and immunohistochemistry, implicating the cadherin–catenin complex in human disease. Evaluation of the cadherin–catenin complex in malignant tumours has improved our understanding of tumour invasion and metastases. In addition, it may provide important prognostic information and may hold answers for future therapeutic intervention.     

Differential expression of E-cadherin and beta catenin in primary and metastatic Wilms's tumours.

BACKGROUND: The E-cadherin-catenin adhesion complex is crucial for intercellular adhesiveness and maintenance of tissue architecture. Its impairment is associated with poorly differentiated phenotype and increased invasiveness of carcinomas. AIMS: To evaluate E-cadherin, beta catenin, gamma catenin, and ezrin expression and its relation to histopathological features of primary and metastatic Wilms's tumours. METHODS: Immunohistochemistry was used to determine the expression and cellular distribution of E-cadherin, beta catenin, gamma catenin, and ezrin in primary and metastatic Wilms's tumours. Western blotting was used to determine polypeptide size and expression of E-cadherin and beta catenin in Wilms's tumours compared with normal kidney. RESULTS: Moderate expression of E-cadherin was found mainly in cytoplasm and occasionally cell membranes of dysplastic tubules, whereas low expression was seen in cytoplasm of blastemal cells. Primary and metastatic tumours showed moderate to high beta catenin expression in blastemal and epithelial cells, with predominantly membranous and cytoplasmic staining. Occasional nuclear staining was noted in metastatic tumours. Low to high gamma catenin and ezrin expression was seen in cytoplasm of blastemal and epithelial cells of primary and metastatic tumours. Higher amounts of 92 kDa beta catenin were detected in tumours than in normal kidney. Low expression of 120 kDa E-cadherin was seen in moderately differentiated tumours, whereas expression was lacking in poorly differentiated tumours. CONCLUSIONS: Compared with primary tumours, metastatic tumours showed lower expression of E-cadherin and gamma catenin, with nuclear staining for beta catenin. Low E-cadherin was associated with poorly differentiated tumours. These results suggest that abnormal expression of adhesion proteins correlates with the invasive and metastatic phenotype in Wilms's tumours.     

Micro-anatomy related antigen expression in melanocytic lesions

The in situ expression of antigens associated with melanosomes (gp-100), pigmentation (PAA), tyrosinase (TRP-1), melanoma (MAA-1/MAA-2), and HLA-DR was investigated immunohistochemically in frozen archival specimens of common acquired melanocytic naevi, in dysplastic melanocytic naevi, and in lymph node metastases of melanoma. Expression of these antigens was also studied in established cultured normal human melanocytes, naevus-derived melanocytes and melanoma cell lines of varying metastatic potential, by immunohistochemistry and flow cytometry. Compared with normal melanocytes, melanocytic naevi exhibited increased expression of gp-100, PAA, and TRP-1 in the lesional cells at or very near the dermo-epidermal junction, but with diminishing expression towards the intra-dermal base of the lesions. In contrast, expression of MAA-1 and MAA-2 was observed in melanocytes throughout the dermal part of the naevi. Melanocytes located at the basal layer of the epidermis were positive only for gp-100, PAA, and TRP-1 antigens. Dysplastic melanocytic naevi showed staining of gp-100, PAA, TRP-1, HLA-DR, MAA-1, and MAA-2 of junctional lesional melanocytes, but less intense than that of common acquired naevi. These antigens were not detectable in the dermal part of the dysplastic naevi. Expression of these antigens in lymph node metastases of melanoma was either positive or negative. Similar results regarding antigen expression were observed in all cultured melanocytic cells, both by immunohistochemistry and by flow cytometry. The present data suggest that analysis of these antigens may contribute to the discrimination of common acquired melanocytic naevi from their dysplastic counterparts. Furthermore, variations in the levels of expression in naevi may be consistently related to the micro-anatomy of the lesions, indicating that the micro-environment may have an influence on the expression levels of these antigens in different lesional melanocytes.     

Histopathological characteristics of malignant melanoma affecting mucous membranes: a unifying concept of histogenesis

AIMS: To investigate histopathological characteristics of melanocytic lesions affecting mucous membranes in various anatomical sites. Particular attention was paid to elucidation of morphological characteristics of early phases of mucosal melanoma in order to contribute to effective detection of this highly malignant neoplasm in the curable stages. METHODS: A total of 87 melanocytic lesions of mucous membranes were investigated histopathologically. There were 55 malignant melanomas including eight lesions of melanoma in situ, three in the radial growth phase (RGP) and 44 in the vertical growth phase (VGP), and 28 benign melanocytic lesions including four melanotic macules, 19 melanocytic naevi and five blue naevi. In addition, this series also included four equivocal lesions for which diagnoses were not definitely determined. With regard to malignant melanoma, histopathological patterns of in situ phase and RGP were intensely evaluated. RESULTS: Histopathological features of benign melanocytic lesions were essentially the same as those of the corresponding lesions of the skin. In the vast majority of mucosal melanomas, irrespective of anatomical sites, the main histopathological pattern seen in melanoma in situ and in RGP was the lentiginous pattern, which shows proliferation of atypical melanocytes in the lower layer of more or less acanthotic epithelium, though subtle variations of the pattern were detected. No association of melanocytic naevus was detected in any cases of melanoma. Based on these findings, we have proposed a unifying concept of de novo histogenesis of mucosal malignant melanoma. CONCLUSIONS: Our concept of histogenesis of mucosal melanoma assists in the identification of this highly malignant neoplasm in the early curable stages.