Monoclonal Antikeratin Research Articles

Histogenesis of mixed tumor of the skin, apocrine type: immunohistochemical study of keratin expression.

To investigate the histogenesis of mixed tumor of the skin, apocrine type, the immunophenotypes of 10 cases were examined using 19 different monoclonal anti-keratin antibodies and antibodies against carcinoembryonic antigen (CEA) and involucrin. By using light microscopy, four epithelial elements in this tumor were characterized: tubular branching structures with lumina lined by cuboidal epithelium and those with lumina lined by columnar epithelium, keratinous cysts, and solid aggregates of epithelial cells. The immunohistochemical patterns of cytokeratin expression suggested that cuboidal and columnar cells differentiated, respectively, toward the ductal and secretory cells of apocrine glands, whereas keratinous cysts revealed follicular infundibular differentiation. Furthermore, CEA expression, a marker for sweat-gland differentiation, was present not only on tubules' luminal surfaces but also on the inner surfaces of keratinous cysts. The simultaneous coexpression of CEA and cytokeratins specific for follicular infundibulum in the keratinous cysts, although perplexing, suggested that keratinous cysts may contain some cells differentiating toward the intrafollicular portion of apocrine ducts that enter infundibulae rather than eccrine ducts that have no infundibular association. We conclude that apocrine type of mixed tumors of the skin demonstrate differentiation toward all components of apocrine units.

Keratin and involucrin expression in discoid lupus erythematosus and lichen planus.

In the present study, keratin and involucrin expression were studied in cutaneous lesions of discoid lupus erythematosus and lichen planus in order to gain a better understanding of the abnormal differentiation or maturation of the epidermal cells in these dermatoses. Ten specimens each from discoid lupus erythematosus and lichen planus were analyzed by immunohistochemical techniques, using a panel of monoclonal antikeratin antibodies and polyclonal anti-involucrin antibody, and five specimens each were analyzed by one- and two-dimensional gel electrophoresis and immunoblot analysis using three antikeratin antibodies. No significant difference was found between the dermatoses. The expression of differentiation-specific keratins showed a similar pattern to that in normal epidermis, and involucrin was expressed even in the lower part of the stratum spinosum. Keratins 6 and 16, which are characteristic markers of hyperproliferative states, and keratin 17 were detected in nonhyperproliferative and atrophic epidermis with hydropic degeneration and inflammatory infiltrates in the dermis. These results suggest that expression of keratins 6, 16 and 17 in discoid lupus erythematosus and lichen planus may reflect a wound healing response to the damage to the basal cell layer, or may be under the control of cytokines produced by infiltrating inflammatory cells in the dermis.

Ovine squamous cell carcinoma: immunocharacterisation of neoplastic cells and peritumoural cellular infiltrate

An immunohistochemical characterisation of neoplastic cells and peritumoural cellular infiltrate of ovine squamous cell carcinomas ( OSCC) in different stages of growth was carried out using a commercially-available panel of seven antibodies, and formalin-fixed and paraffin-embedded tissue samples. Neoplastic cells reacted with the anti-keratin monoclonal antibody RCK-102 and with an anti-keratin polyclonal antibody, whereas they were unreactive with the anti-keratin monoclonal antibody NCL-5D3. The tumour cells were unreactive With the anti-vimentin polyclonal antibody. Increased numbers of CD3+ T-lymphocytes, IgG-containing plasma cells and lysozyme+ macrophages were associated with precancerous lesions (actinic keratosis) and with early OSCC. These results show that early lesions of OSCC induce an in situ cellular and humoral immune response. In advanced OSCC, the number of CD3+ T-lymphocytes and macrophages in the peri- and intratumoural cellular infiltrate remained high, whereas a significant decrease of IgG-containing plasma cells was found compared with early OSCC. This finding suggests an in situ decrease in the Immoral immune response in advanced OSCC.

Increased expression of cytokeratins 14, 18 and 19 correlates with tumor progression in the uterine cervix.

The expression of cytokeratins (CKs) in normal cervical epithelium, low grade squamous intraepithelial lesions (SIL), high grade SILs and squamous cell carcinoma (SCC) were analyzed using four different monoclonal antikeratin antibodies. In normal cervical epithelium, CK 18 showed strong immunoreactivity in basal and parabasal layers. CK 19 and 14 were expressed only in the basal layer while CK 13 was found selectively n the spinal cells. As the lesions progressed from low grade SIL to high grade SIL, immunoreactivity of CK 18, 19 and 14 in the basal cell compartment increased while the expression of CK 13 decreased. In SCC, as well-differentiated tumors showed decreased immunoreactivity for CK 18, 19 and 14 with CK 13 showing a strong and focal (localized) immunoreactivity. Undifferentiated carcinomas totally lacked CK 13 reactivity. Our findings therefore suggest that expression of CK 18, 19 and 14 may be directly related to tumor grade and CK 13 may be a marker of differentiation in cervical lesions.

Cytokeratin 18 expression in squamous cell carcinoma of the head and neck.

Cytokeratin (CK) expression was studied in squamous cell carcinomas of different subsites in the head and neck by using cryostat sections from 27 head and neck squamous cell carcinomas (HNSCCs) and 6 cell lines established from HNSCC. All tissues were analyzed immunohistochemically with a panel of monospecific anti-keratin monoclonal antibodies. Most carcinomas recapitulated the expression pattern of keratins present in the basal layer of normal epithelium from the site of tumor origin. Regional differences in the expression of simple-epithelial type of keratins in stratified (pseudostratified) epithelia were to a large extent repeated in corresponding carcinomas. In the present study, localization of various keratins were surveyed and CK 18 specific monoclonal antibodies were specifically used to distinguish SCCs of the larynx or hypopharynx from SCCs of the oral cavity. CK 18 staining of almost all tumor cells was detected in 11 of 12 SCCs of the larynx and hypopharynx, but was only detected sporadically in 3 of 9 SCCs of the oral cavity. The present results show that CK 18 typing might be useful for distinguishing sites of origin of various HNSCCs. Findings also indicate that CK 18 expression in SCC might be modulated by microenvironmental factors.

右肘皮下に生じたメルケル細胞癌の１例

A 58-year-old Japanese female with Merkel cell carcinoma is described. She noted her subcutaneous nodule on her right elbow about two years before visiting our dermatological out patient clinic. Light microscopy revealed that the tumor cells showed a trabecullar organoid growth pattern and were localized mainly in subcutane ous tissues. The individual cells were round and uniform in size and shape. Immunocytochemically, tumor cells were positiveiy stained with rabbit anti-neuron specific enolase antibody as well as RGE53 and HKN-4 anti-keratin monoclonal antibodies. Electron microscopy demonstrated dense core granules and intermediate filaments in the tumor cells. From the features mentioned adove, we diagnosed her subcutaneous tumor as Merkel cell carcinoma. Management; she underwent the wide resection of the tumor and dissection of the right axillary lymphnodes. In addition she received radiotherapy for primary lesion and chemotherapy as follows; CDDP+ ADM+VCR+ETP.

Differential intrastromal invasion by normal ocular surface epithelia is mediated by different fibroblasts

For most mucosal epithelia including the ocular surface, it is generally believed that wound healing is executed by epithelial migration on the plane of erosion or ulceration. In explant cultures, we incidentally observed the phenomenon of intrastromal invasion by corneal, limbal and conjunctival epithelial cells even when cell migration on plastics was promoted. Homotypic and heterotypic tissue recombinants between corneal and conjunctival epithelial cells and their stroma revealed that this phenomena was dependent on viable mesenchymal cells and was more active in conjunctival stroma than corneal stroma. Using organotypic cultures in which 3T3 fibroblasts were incorporated in collagen gel, we noted that this phenomenon was fibroblast-dependent and up-regulated by lifting the culture to the air-fluid interphase. The extent of intrastromal invasion was decreased if 3T3 fibroblasts were treated with increasing concentrations of mitomycin C. The invading epithelial islands retained the same basal and suprabasal epithelial phenotypes as those of the surface epithelial layers using several anti-keratin monoclonal antibodies. Using 5-fluorouracil (5-FU) to eliminate the rapid-cycling, i.e. transient amplifying progenitor basal cells, we further noted that this phenomenon could still be produced by 5-FU-resistant slow-cycling progenitor cells of corneal, limbal and conjunctival explants. In organotypic cultures, conjunctival fibroblasts were more active than corneal fibroblasts in inducing corneal or conjunctival epithelial invasion. As such intrastromal invasion can experimentally be produced by normal non-transformed adult epithelial cells and mediated by fibroblasts, this in vitro phenomenon may be useful for studying the epithelial-mesenchymal interactions operating during embryonic development and post-natal wound healing.

Eccrine syringofibroadenoma. Report of a case and immunohistochemical study of keratin expression

We report a 49-year-old woman with an eccrine syringofibroadenoma. An asymptomatic nodule appeared on the right heel, and subsequently enlarged gradually. Histological examination revealed anastomosing strands of pale epithelial cells, with occasional duct formation and mucinous fibrovascular stroma. There were two types of strands: thick and thin. Immunohistochemical study, using a panel of monoclonal antikeratin antibodies, revealed that the immunoreactivity differed between the two types of strands. The thick strands showed a staining pattern similar to the uppermost portion of the intradermal duct, and the thin strands showed a pattern similar to the other portion of the duct. This observation suggests that the thick and thin strands differentiate towards the uppermost portion and the remainder of the duct, respectively.

Immunohistochemical characterization of keratin expression in clear cell acanthoma.

The nature of clear cell acanthoma has not been clarified, although many hypotheses have been proposed, including a benign neoplasm derived from epidermis or the acrosyringium, or a non-specific dermatosis. In this study, seven cases of clear cell acanthoma were analysed by immunohistochemical techniques, using various monoclonal antikeratin antibodies, and antibodies against filaggrin, involucrin and epithelial membrane antigen. Different immunoreactivities were noted between clear cell acanthoma and a normal eccrine gland, including the acrosyringium. Immunoreactivities of clear cell acanthoma were almost identical to those of normal epidermis, although some antibodies gave a different staining pattern between clear cell acanthoma and normal epidermis. The expression of cytokeratins in psoriatic epidermis has been reported to change as a result of abnormal differentiation or maturation. Clear cell acanthoma showed a similar staining pattern to inflammatory dermatoses such as psoriasis vulgaris, lichen planus and discoid lupus erythematosus. We speculate that clear cell acanthoma is a localized form of inflammatory dermatosis rather than a neoplasm.

Relative Amounts of Keratin 17 Are Higher Than Those of Keratin 16 in Hair-Follicle-Derived Tumors in Comparison with Nonfollicular Epithelial Skin Tumors

Specimens of trichilemmal cyst, malignant trichilemmoma, keratoacanthoma, and epidermal cyst were examined to characterize keratin peptides in hair-follicle-derived tumors. Keratins were extracted from the specimens and analyzed by two-dimensional gel electrophoresis and densitometry; the results were then compared with those for normal epidermis, the outer root sheath of hair follicles, psoriatic epidermis, and various nonfollicular cutaneous epithelial tumors. The specific nonfollicular tumors examined were squamous cell carcinoma, Bowen disease, actinic keratosis, eccrine porocarcinoma, and sebaceous carcinoma. Immunohistochemistry also was performed with a few anti-keratin monoclonal antibodies. As a general rule, K6 and K16 were expressed in hyperproliferative conditions, such as epidermal tumors, and K17 was coexpressed in the same lesions. The ratio of K16 to K17 in many epithelial skin tumors has been unclear until now. K17 content exceeded K16 content in most follicular tumors, whereas in almost all the nonfollicular tumors and the psoriatic epidermis, K17 levels were less than or about equal to K16 levels. There was a significant difference in the ratio of K16 to K17 between follicular and nonfollicular skin tumors. These results indicate that alterations in the content of these keratins may be associated with follicular differentiation.

４‐Ｎｉｔｒｏｑｕｉｎｏｌｉｎｅ １‐ｏｘｉｄｅ誘発ラット舌癌におけるＥＧＦレセプターの免疫組織化学的研究

Immunohistochemical changes of epidermal growth factor receptor (EGFR) during the genesis of tongue carcinomas were studied in male SD rats administered 50ppm 4NQO p.o. for 12 weeks. Paraffin sections were examined with immunohistochemical meth ods using monoclonal anti-EGFR antibody (clone F4), polyclonal anti-EGF antibody, polyclonal anti-TGFα antibody, monoclonal anti-keratin antibody (clone KL1), and monoclonal anti-PCNA antibody (clone PC10) by the ABC method. Immunoblotting for EGFR and keratin was evaluated at 170 k Da and 56 k Da bands. EGFR was expressed in the cell membrane of both non-tumorous epithelial cells and carcinoma cells, and EGFR staining was mostly distributed in the spinous cells of the normal epithelium and its hyperkeratotic or dysplastic counterpart. The staining level of the basal cells was much weaker. In the hyperkeratotic epithelium, the intensity of the staining was stronger than that in the normal epithelium. In carcinoma, EGFR expression was found in the highly differentiated areas of the surrounding cancer pearl, but there was no expression in peripheral tumor calls corresponding to basal cells. Keratin (KL1) reaction was noted in keratinocyte and keratinizing tumor cells, and KL1 positive cells were irregularly distributed in line with keratinization. Such irregular expression of higher molecular weight keratin occured parallel to individual cell keratinization or dysplasia. PCNA positive nuclei were confined to the basal cells and proliferating tumor cells. Immunostaining of EGF and TGFα was limited to the cytoplasm of the spinous cells in normal epithelium and induced carcinoma.These results suggested the following:1) In the rat tongue carcinoma induced by 4NQO, EGFR may react by autocrine mechanism of EGF/TGFα during carcinogenesis.2) Abnormal EGFR expression in carcinoma cells may be involved in malignant transformation.3) EGF/TGFα-EGFR interaction may be involved in processes after cell division or proliferationboth in the normal epithelium and in squamous cell carcinoma.4) EGF/TGFα-EGFR interaction may play a part in the control of keratin production in epithelial cells under a physiological environment, and EGFR may be more intimately involved in squamous cell differentiation rather than in cell proliferation in squamous cell epithelium and squamous cell carcinoma.

Immunohistochemical staining patterns of keratins in normal oesophageal epithelium and carcinoma of the oesophagus.

To clarify the keratin staining patterns of invasive carcinoma of the oesophagus, 22 cases of formalin-fixed paraffin-embedded surgical specimens were examined immunohistochemically with the labelled streptavidin biotin method using a panel of six different monoclonal anti-keratin antibodies. The antibody reacted adequately when antigen was retrieved in a microwave oven, and the relationship between morphological characteristics and keratin reaction patterns was analyzed in carcinomas and compared with adjacent histologically normal epithelium. In the normal oesophageal epithelium, AE3 and CK8.12 labelled all layer of cells, KS-1A3, E3 and KL1 labelled suprabasal cells, and LL002 selectively labelled the basal cells. In squamous cell carcinomas, AE3, CK8.12, KL1 and LL002 labelled almost all the tumour cells regardless of their differentiation, E3 only labelled keratinized cells, while marked decrease or loss of KS-1A3 staining was seen in all cases examined. Therefore, the characteristic profile of squamous cell carcinoma was a strong and diffuse expression of keratin 14 and 16, strong but localized expression of keratin 17, and loss of keratin 13 expression. Undifferentiated carcinoma totally lacked all keratin reactivity. The findings suggested that the neoplastic epithelial cells showed different keratin reactivity and distribution compared to normal oesophageal epithelium. In addition, histologically normal epithelium, dysplasia and carcinoma-in-situ adjacent to or overlying carcinoma expressed keratin 14.

Clinicopathologic and Immunohistochemical Studies on Lichen Amyloidosis and Macular Amyloidosis

Different authors have showed the epidermal origin of amiloyd in lichen amyloidosis (LA) and macular amyloidosis (MA).¹We examined eight consecutive patients suffering from LA, MA, or biphasic amyloidosis (BA) in a clinicopathologic study characterizing amyloid deposits with several monoclonal antikeratin antibodies and establishing immunohistochemical differences among the three disorders. <h3>Patients, Materials, and Methods.</h3> Biopsy specimens were taken from all patients and divided into two portions. Half of the specimen was formalin-fixed, paraffin-embedded, and processed for hematoxylin-eosin, Congored, and thioflavine T staining. Samples were scored as positive or negative for the presence of amyloid deposits in the epidermis; papillar, middle, or deep dermis; and perivascular or periadnexial area. The other half was snap frozen in liquid nitrogen and processed for immunohistochemistry (avidin-biotin complex technique,<b>Table</b>). <h3>Results.</h3> Patients 1 and 2 had MA, patients 2 through 6 had LA, and patients 7 and 8 had BA. Their mean age was

Immunohistochemical assessment of individual tumor cells in lymph nodes of patients with non-small-cell lung cancer.

This prospective study was designed to evaluate the prognostic relevance and biologic characteristics of a minimal lymphatic tumor load in non-small-cell lung cancer (NSCLC). Frozen-tissue sections from 391 regional lymph nodes of 72 patients with completely resected NSCLCs, who were staged as free of metastases (pT1-3, pN0,M0,R0) by clinical tumor staging procedures and histopathologic examinations, were studied. For tumor-cell detection, we applied the alkaline phosphatase-antialkaline phosphatase (APAAP) immunostaining technique with monoclonal antibody Ber-Ep4 against two glycoproteins of 34 and 49 kd present of the surface and cytoplasm of epithelial cells. Individual Ber-Ep4-positive cells were detected in 11 of 72 (15.2%) cancer patients, while positive staining was consistently absent in all sections from control nodes of 24 noncarcinoma patients. No correlation between a positive lymph node finding and either the size or differentiation grade of the primary tumor or the presence of micrometastatic tumor cells in bone marrow assessed by immunocytochemistry with antikeratin monoclonal antibody CK2 was observed. Following a median observation time of 26.0 months (range, 15 to 39), patients with lymph node micrometastases showed a significantly shorter disease-free survival duration than node-negative patients (log-rank test, P = .005). The independence of this prognostic significance was demonstrated by a multivariate analysis (Cox regression model, P = .005). Our results provide evidence that the presence of single lung carcinoma cells in lymph nodes is an independent indicator of the disseminatory capacity of an individual primary tumor. Immunohistochemical assessment of micrometastases in lymph nodes is recommended for current tumor staging in NSCLC, as it might lead to better stratification of patients for adjuvant therapy.

Immunohistochemical characterization of keratin expression in clear cell acanthoma

Summary The nature of clear cell acanthoma has not been clarified, although many hypotheses have been proposed, including a benign neoplasm derived from epidermis or the acrosyringium, or a non-specific dermatosis. In this study, seven cases of clear cell acanthoma were analysed by immunohistochemical techniques, using various monoclonal antikeratin antibodies, and antibodies against filaggrin, involucrin and epithelial membrane antigen. Different immunoreactivities were noted between clear cell acanthoma and a normal eccrine gland, including the acrosyringium. Immuno-reactivities of clear cell acanthoma were almost identical to those of normal epidermis, although some antibodies gave a different staining pattern between clear cell acanthoma and normal epidermis. The expression of cytokeratins in psoriatic epidermis has been reported to change as a result of abnormal differentiation or maturation. Clear cell acanthoma showed a similar staining pattern to inflammatory dermatoses such as psoriasis vulgaris, lichen planus and discoid lupus erythematosus. We speculate that clear cell acanthoma is a localized form of inflammatory dermatosis rather than a neoplasm.

Ultrastructure of Human Skin by a Rapid Freezing Technique: Structural Preservation and Antigenicity

To investigate the natural fine structure of skin, human skin biopsies were studied by electron microscopy and immunoelectron microscopy using rapid freezing and freeze-substitution techniques. Well-preserved structures were observed within a depth of 20 microns from the slammed surface of the samples. Epidermal cells were always closely located with very narrow intercellular spaces. Keratin filaments were distributed densely and homogeneously without forming bundles in the cytoplasm of epidermal keratinocytes. Langerhans cell granules were composed of a flat vesicular portion and an oval rod portion. The most striking finding was in the dermal-epidermal junction, where the lamina densa was present but no lamina lucida was observed. Further, by immunoelectron microscopy with anti-keratin monoclonal antibody, the 20-microns-deep part of the samples revealed the most significant staining. These findings indicate that the ultrastructure of routinely processed skin samples may be modified during the procedure for conventional chemical fixation and dehydration and that the ultrastructurally most preserved specimens, reflecting the conditions close to natural in vivo structures of the skin, can be obtained by the techniques described in this paper.

Identification of a keratin-associated protein that localizes to a membrane compartment.

We describe the characterization of an acidic glycoprotein (molecular mass approximately 85 kDa) that associates with keratin intermediate filaments of 'simple'-type epithelia. Using a number of anti-keratin monoclonal antibodies, the 85 kDa glycoprotein was identified by co-immunoprecipitation with keratin polypeptides 8 and 18 (K8/18) from the human colonic epithelial cell line HT29 and several other epithelial cell lines. This Keratin-Associated Protein (termed KAP85) was readily detected after in vitro galactosylation of K8/18 immunoprecipitates obtained from mitosis-arrested cells. Its solubilization and detection were dependent on the detergent used, and it was barely detected after in vitro galactosylation of asynchronously growing G0/G1-phase cells. Its poor in vitro galactosylation in G0/G1-phase cells is likely a reflection of the lack of available terminal N-acetylglucosamine residues, since it can be labelled to a similar extent in G0/G1- and G2/M-phase cells using NaIO4/NaB3H4. Glycosidase digestion showed that KAP85 contains high mannose and complex oligosaccharides. Fractionation of total cellular K8/18 into soluble and cytoskeletal insoluble pools showed that KAP85 associates exclusively with the cytoskeletal K8/18 pool. Subcellular fractionation showed that KAP85 co-localizes with a plasma-membrane-enriched fraction that includes the transferrin receptor and KS-1 antigen. Our results demonstrate in vitro evidence of a membrane-associated glycoprotein (KAP85) which may serve as an attachment site for filamentous K8/18.

Neuroendocrine carcinoma of the skin (Merkel cell carcinoma). An immunoelectron-microscopic case study.

An unusual tumor with a controversial name as well as histogenesis, the neuroendocrine carcinoma of the skin (also known as "Merkel cell carcinoma," "trabecular carcinoma of the skin") has previously been extensively studied by immunohistochemical methods at the light-microscopic level. Ultrastructural descriptions of this tumor have also been extensive, although immunocytochemical study of this neoplasm at the electron-microscopic level has been limited. In this report, we have used postembedding protein A-gold immunocytochemistry on thin sections from tumor embedded in Lowicryl K4M to investigate the expression and ultrastructural localization of a panel of commercially available, diagnostically useful antibodies. Antibodies associated with epithelial derivation included anti-keratin monoclonal antibody AE1/AE3, polyclonal anti-keratin, and monoclonal anti-cytokeratin cocktail (MAK-6), as well as a monoclonal antibody against epithelial membrane antigen (EMA). Antibodies associated with neuroendocrine derivation included monoclonal anti-chromogranin A and monoclonal anti-synaptophysin. Although staining with a polyclonal antibody directed against neuron-specific enolase (NSE) was equivocal, there was no labeling with a monoclonal anti-neurofilament antibody. The finding of positive keratin labeling of filaments arranged in paranuclear aggregates correlates well with the previously described immunohistochemical staining pattern at the light-microscopic level. Moreover, the presence of cytoplasmic synaptophysin and chromogranin positivity over dense-core granules exemplifies the neuroendocrine differentiation present in this fascinating tumor of the skin.

A monoclonal antibody epitope on keratin 8 identified using a phage peptide library

A bacteriophage random hexapeptide library was used to define the epitope of a monoclonal anti-keratin antibody. Phage selected by the keratin 8-specific antibody LE41 displayed highly related sequences on their pIII coat protein. The consensus sequence S(X)LNP allowed the precise localization of an LE41 epitope (SLLSP) within the head domain (H1 subdomain) of human keratin 8, known to be important for correct filament polymerisation. By sequencing the immunizing antigen, keratin 8 from Potorous tridactylis, it was shown that the natural epitope of LE41 is the pentapeptide SLLNP, which confirmed predictions from the phage library results. An SLL(X)P motif is found in the H1 region of all type II keratins (keratins 1 to 8) in different species, but mutational analysis revealed that LE41 can only bind to keratin 8 when Asn (N) or Ser (S) is found in the (X) position. Thus the monoclonal antibody LE41 retains its specificity for keratin 8, dependent on a single amino acid residue, even though it recognizes an epitope within the highly conserved H1 subdomain of the head region. Six other monoclonal antibodies tested on the phage library failed to select motifs.

A comparative study of cytokeratin expression in paget cells located at various sites

Extramammary Paget disease appears in anogenital, axillary, or other areas. In this study, the authors addressed the question of whether the histogenesis of 35 cases of Paget disease arising at different sites was the same. Specimens of 35 cases of extramammary Paget disease (16 genital; 9 invasive carcinomas of genital; 6 axillary; 1 periumbilical; and 3 perianal), 4 cases of mammary Paget disease, 4 cases of breast carcinomas, and 6 cases of anal carcinomas of perianal spread from primary rectal adenocarcinomas were retrieved and stained by the avidin-biotin-complex method, using various kinds of monoclonal antikeratin antibodies. There was no significant difference in cytokeratin expression among these cases of extramammary Paget disease. Simple epithelial keratins were expressed in Paget cells in extramammary Paget disease, but no expression of differentiation-specific or noncornifying stratified squamous epithelial keratins was observed, regardless of the degree of invasion. Paget cells in extramammary Paget disease revealed a similar cytokeratin expression to that in secretory cells of normal apocrine or eccrine glands. In addition, there was no significant difference in cytokeratin expression in tumor cells among extramammary and mammary Paget disease, breast carcinomas, and anal carcinomas. Cases of Paget disease arising at different locations could not be distinguished from each other based on cytokeratin expression. In addition, antikeratin antibodies against simple epithelial keratins were demonstrated to be more useful for the identification of Paget cells in the paraffin sections than were conventional antibodies, such as an antibody against carcinoembryonic antigen (CEA).