Benign Epidermal Tumors Research Articles

7,3′,4′-Trihydroxyisoflavone, a Metabolite of the Soy Isoflavone Daidzein, Suppresses Ultraviolet B-induced Skin Cancer by Targeting Cot and MKK4

Nonmelanoma skin cancer is one of the most frequently occurring cancers in the United States. Chronic exposure to UVB irradiation is a major cause of this cancer. Daidzein, along with genistein, is a major isoflavone found in soybeans; however, little is known about the chemopreventive effects of daidzein and its metabolites in UVB-induced skin cancer. Here, we found that 7,3',4'-trihydroxyisoflavone (THIF), a major metabolite of daidzein, effectively inhibits UVB-induced cyclooxygenase 2 (COX-2) expression through the inhibition of NF-κB transcription activity in mouse skin epidermal JB6 P+ cells. In contrast, daidzein had no effect on COX-2 expression levels. Data from Western blot and kinase assays showed that 7,3',4'-THIF inhibited Cot and MKK4 activity, thereby suppressing UVB-induced phosphorylation of mitogen-activated protein kinases. Pull-down assays indicated that 7,3',4'-THIF competed with ATP to inhibit Cot or MKK4 activity. Topical application of 7,3',4'-THIF clearly suppressed the incidence and multiplicity of UVB-induced tumors in hairless mouse skin. Hairless mouse skin results also showed that 7,3',4'-THIF inhibits Cot or MKK4 kinase activity directly, resulting in suppressed UVB-induced COX-2 expression. A docking study revealed that 7,3',4'-THIF, but not daidzein, easily docked to the ATP binding site of Cot and MKK4, which is located between the N- and C-lobes of the kinase domain. Collectively, these results provide insight into the biological actions of 7,3',4'-THIF, a potential skin cancer chemopreventive agent.

Treatment of Keratoacanthoma with 5% Imiquimod Cream and Review of the Previous Report

Keratoacanthoma (KA) is a benign epidermal tumor, characterized by rapid and abundant growth, a tendency toward spontaneous regression and histopathologic similarity to squamous cell carcinoma (SCC). Because KA can be easily misdiagnosed as SCC, surgery is considered the treatment of choice. Recently, regression of KAs following application of 5% imiquimod cream (Aldara®) has been reported. We present 4 cases of KA treated with topical imiquimod, applied 3 to 4 times a week. Obvious improvement was observed after 4 to 6 weeks of application and the lesions were almost cleared leaving scars after 9 to 11 weeks. These results show that topical imiquimod can be an effective option for the conservative management of KA as previously reported. We also suggest that lesions treated with imiquimod cream should be considered for biopsy to judge histopathological remission after 5 to 8 weeks of application to shorten the duration of the treatment.

Multiple eruptive clear cell acanthoma

Clear cell acanthoma is a rare solitary benign epidermal tumor of unknown etiology. The disease arises in the middle-age, with no sex predominance. It appears as a single reddish papule or papule-nodule and a peripheral scaling collarette is characteristic. Although solitary lesions are the rule, less than 30 cases of multiple Clear cell acanthoma have been described in the literature to date. We report an unusual case of a healthy 74-year-old male with multiple clear cell acanthoma on the lower extremities treated successfully with cryotherapy. Despite significant progress in treatment of clear cell acanthoma, cryotherapy, based on liquid nitrogen, remains an important alternative in treating multiple clear cell acanthomas.

Cathepsin K-upregulation in fibroblasts promotes matrigel invasive ability of squamous cell carcinoma cells via tumor-derived IL-1α

Cathepsin K (CTSK), a cysteine protease with strong collagenolytic properties, is involved in extracellular matrix turnover. In the previous studies, CTSK expression was detected in peritumoral fibroblasts (Fbs) around squamous cell carcinoma (SCC), but not in those surrounding benign epidermal tumors. However, the mechanism governing CTSK expression in epidermal tumors remains unclear. To study the regulatory mechanisms of fibroblastic CTSK expression in the SCC-stromal interaction. We examined dynamic interactions of Fbs with tumorigenic SCC cells (A431 and A253) or normal human keratinocytes. SCC cells and normal keratinocytes did not synthesize CTSK, while Fbs constitutively expressed CTSK. When cocultured, SCC cells upregulated fibroblastic CTSK expression more potently than did normal keratinocytes, which was mainly attributable to SCC-derived IL-1α. Coculturing Fbs with SCC cells significantly augmented the matrigel invasive ability of SCC cells, which was downregulated when cocultured with CTSK knockdown Fbs or in the presence of neutralizing anti-IL-1α antibody. The CTSK-upregulated Fbs generated by SCC-derived IL-1α may play a crucial role in the progression and invasion of SCC.

Report: Clear cell acanthoma: a rare clinical diagnosis prior to biopsy

AbstractBackground Clear cell acanthoma is a rare, benign epidermal tumor with a clinical hybrid appearance and a distinct histological one. It is frequently mistaken for other clinical lesions.Objective To evaluate the frequency that clear cell acanthoma was listed in the clinical differential diagnosis of histologically confirmed specimens.Methods A regional dermatopathology lab database was evaluated from January 1998 through March 2008 for histologically diagnosed cases of clear cell acanthoma. Clinical data that was submitted with these cases including differential diagnoses was analyzed.Results During this time period of review, 411 histologically confirmed cases of clear cell acanthoma were identified. This entity was listed as a diagnostic possibility in 11 (2.7%) of the cases.Conclusion Clear cell acanthoma was rarely listed amongst the differential diagnosis of biopsy proven specimens. This may be due to a variable clinical appearance with overlapping features of several other lesions making it difficult to distinguish, or an entity that is rare and not frequently suspected. Additional studies with dermatoscopy may help to further delineate the reasons for the low diagnostic sensitivity.

Postępowanie w przypadkach wznowy brodawczaka odwróconego nosa i zatok przynosowych po leczeniu operacyjnym w materiale Kliniki Otolaryngologii Warszawskiego Uniwersytetu Medycznego

Inverted papilloma is benign epidermal neoplasm of not recognized etiology. The lesion is estimated to represent 0.5-4% of sinonasal tumors. Generally inverted papilloma is unilateral, arises from the lateral nasal wall and characterizes with local destruction and rapid growth. The tumor can possibly undergo malignant transformation. The treatment of choice is surgery, recently endoscopic approach is considered to be superior to the open approach. was evaluation of recurrent inverted papilloma treatment results in the experience of Otolaryngology Department, Medical University of Warsaw, from 1982 to 2009. The group of 124 patient (66 men and 58 women) aged from 26 to 79 with inverted papilloma operated between 1982 and 2009 were enrolled in the study. Follow up was from 6 months to 27 years. Most common primary localization of the tumor was combined lateral nasal wall and maxillary sinus (42%). In 37% the lesion involved unilaterally the lateral nasal wall, maxillary sinus and ethmoid sinuses, rarely it was localized only in the lateral nasal wall (16.1%) and exclusively in the nasal septum (4.8%). All the patients were treated surgically, 46% of patients underwent endoscopic procedure, 37.1% lateral rhinotomy, 15% Denker rhinotomy and 1.6% midfacial degloving. Recurrence was observed in 15.3% including 57.9% after endoscopic surgery, 26% after Denker operation and 15.8% after lateral rhinotomy. Malignant transformation was observed in 5 patient (4%). All the patients with recurrent inverted papilloma were treated surgically, 5.3% of patient underwent midfacial degloving, 5.3% Caldwell-Luc operation, 10.5% endoscopic procedure, 26.3% Denker operation and 52.6% lateral rhinotomy. 1. Endonasal and open approach should be considered in the surgical treatment of recurrent inverted papilloma. 2. Endoscopic approach is preferred in the recent years but qualification for each method should depend on lesion localization, extent and volume. 3. Regular follow-up enables early recurrence diagnosis and treatment.

A Case of Polypoid Clear Cell Acanthoma on the Nipple

Clear cell acanthoma (CCA) is a rare benign epidermal tumor. It usually presents as a flat nodule or dome-shaped plaque and is often localized on the legs of the elderly. We observed an unusual case of polypoid CCA on the nipple of a 14-year-old girl. At present, a few cases of CCA on the nipple area have been reported in the literature. However, CCA presented as a polypoid tumor on the nipple area has been reported very rarely. We herein report the very rare case of polypoid CCA on the nipple and suggest that CCA should be included in the clinical differential diagnosis of polypoid lesions on the nipple.

Are All Seborrheic Keratoses Benign? Review of the Typical Lesion and Its Variants

Seborrheic keratosis (SK) is one of the more common benign epidermal neoplasms seen in adult and middle-aged patients. As little is written in the literature about the variants of SK, this article aims to categorize and discuss the different subtypes and their important associations. An in-depth literature search using OVID Medline and PubMed was conducted to classify the various subtypes of SK. Clinical variants were photographed and used to help document the subtypes. The pathology is described for each. Six subtypes of SK were identified: dermatosis papulosa nigra, stucco keratosis, inverted follicular keratosis, large cell acanthoma, lichenoid keratosis, and flat seborrheic keratosis. Although the etiology and pathogenesis of SKs are still largely debatable, several underlying mechanisms and contributing factors have been identified. All subtypes represent benign lesions, and treatment is usually done for cosmetic reasons. Several of the subtypes may act as cutaneous markers for internal malignancy and should be monitored closely for any atypical changes. Although all subtypes of SK are benign, their association with other malignant lesions and ability to serve as cutaneous markers of internal malignancy emphasize the importance of correctly identifying all variants.

Clear-Cell Acanthoma Versus Acanthosis: A Psoriasiform Reaction Pattern Lacking Tricholemmal Differentiation

Clear-cell acanthoma (CCA) has been reported to be a benign epidermal neoplasm; however, several authors have suggested alternative differentiation as well as other nosologic categories, including a reactive dermatosis. Fourteen CCAs, ten tricholemmomas, and seven cases of psoriasis were reviewed with conventional microscopy, periodic acid-Schiff stains, and immunohistochemical stains. Twelve of fourteen (86%) CCAs were associated with underlying or adjacent conditions. The CCAs stained immunohistochemically in a pattern similar to normal epidermis and psoriasis. Tricholemmomas stained in a distinctly different pattern with MNF116 and NGFR/p75. These cases demonstrate CCA in settings that reflect chronic inflammation, primarily scars and stasis dermatitis, and with an immunophenotype that parallels psoriasis. These findings support the contention that CCA does not show outer follicular sheath (tricholemmal) differentiation. Furthermore, these cases lend additional support to the contention that CCA represents a psoriasiform reaction pattern, which, in appropriately taken biopsies, usually has a demonstrable associated condition. Nonetheless, the precise nosology of this phenomenon has yet to be elucidated completely.

The regression of a canine Langerhans cell tumour is associated with increased expression of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA.

Canine cutaneous histiocytoma is a benign epidermal neoplasm of Langerhans cell origin, which usually displays spontaneous regression. Based on the degree of lymphocytic infiltration, 30 histiocytomas were classified into four groups representing different stages of tumour regression. To elucidate further the mechanisms of the antitumour immune response CD3+, CD21+, CD4+, CD8+ and myeloid/histiocyte antigen+ inflammatory cells were differentiated by immunohistochemistry and quantified. In addition, the number of apoptotic cells was detected using the TdT-mediated biotin-dUTP nick-end labelling (TUNEL) method. Furthermore, the expression of interleukin- (IL-2), IL-12(p40), tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), IL-10 and transforming growth factor-beta (TGF-beta) as well as inducible nitric oxid synthase (iNOS) mRNA was determined by reverse transcription-polymerase chain reaction (RT-PCR). Phenotyping of inflammatory cells revealed a significantly increased infiltration of all lymphocyte subsets and myeloid/histiocytic cells with the onset of tumour regression. The latter was significantly correlated to up-regulation of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA expression. Expression of remaining cytokines and percentage of apoptotic cells showed no group-specific changes. The results indicate an initial infiltration of CD4+ T cells followed by increased expression of Th1 cytokines and recruitment of antitumour effector cells as the principal mechanism for tumour regression. Canine cutaneous histiocytoma is a unique example for an effective immune response in a naturally occurring neoplasm derived from epidermal Langerhans cells and might represent a valuable animal model to investigate tumour immunity.

Unilateral naevoid trichoepitheliomas on the face of a child

Trichoepitheliomas are benign epidermal appendage tumours that present most commonly as solitary lesions, and less often as multiple, symmetrically distributed lesions on the face, scalp, neck and trunk. Only a few patients have been reported in whom trichoepitheliomas were found as unusually configured linear or plaque-like confluent lesions, all of which occurred in patients with skin types V or VI. We describe a white girl with a hemifacial plaque of confluent naevoid trichoepitheliomas, the first report of such lesions in a white patient.

Seborrhoeic keratoses with associated lesions: A retrospective analysis of 85 lesions

Seborrhoeic keratoses are benign epidermal neoplasms that are rarely associated with other skin lesions especially malignancies. In this study, the aim was to assess the incidence of associated lesions occurring either adjacent to or contiguous with a seborrhoeic keratosis. A retrospective case series over a 12-month period was carried out. In total, 639 consecutive histologically diagnosed seborrhoeic keratoses were identified, of which 85 (9%) were found to be associated with other lesions. Of these associated lesions, 44 (7%) were malignant, with four of these found to be arising within the seborrhoeic keratosis. These associated lesions included premalignant lesions, malignancies, melanocytic lesions and miscellaneous lesions. Men (59%) were affected more commonly than women. The average age was 74 years (range 33-98 years). Seborrhoeic keratoses associated with other lesions were found most commonly on the head and neck. The incidence of associated lesions, in particular malignancy arising within seborrhoeic keratoses may be higher than previously thought. This may be an incidental phenomenon, or seborrhoeic keratosis could represent a precursor lesion. Therefore, seborrhoeic keratoses that have undergone recent clinical change should be considered for biopsy and histological examination.

Dexamethasone inhibits MEK1-related epithelial tumours in vivo

9546 Background: The ras/MEK/ERK pathway is implicated in the progression of epithelial carcinomas. In our transgenic mouse model, constitutively active MEK1 is expressed in keratinocytes in the suprabasal layers of the epidermis. We have characterised a T-cell rich, dense inflammatory infiltrate, in the dermis of MEK1 mice and observed benign epidermal tumours at suspected sites of injury. Punch-biopsy wounding induced benign tumours in 38 of 92 (41.3% 95% confidence interval (CI) 32%–52%) MEK1 mice and no tumours occurred in 44 transgene negative mice. We investigated a possible interaction between the inflammatory infiltrate and keratinocyte proliferation by comparing the proportion of MEK1 mice that developed tumours after wounding only against wounding and dexamethasone treatment, a potent anti-inflammatory agent. Methods: Age-matched, wounded, MEK1 transgenic mice were allocated to either a no treatment control group or a treatment group of dexamethasone 100mcg (3mg/kg/day by sub-cutaneous injection) for 30 days from the day after wounding. Mice were observed daily for 60 days for tumour development. The time to tumour development was recorded. Results from 2 independent experiments have been pooled. Results: Tumours developed in 15 of 37 (40.5% 95% CI 26%–57%) MEK1 mice in the no treatment group and in 4 of 38 (10.5% 95% CI 4%–25%) MEK1 mice in the dexamethasone group (Fisher’s exact test, two-sided p-value=0.0035). The difference in proportions of the 2 groups developing tumours is 0.3 (95% CI 0.11–0.49). The relative risk of wound-induced tumours with no treatment is 3.85 (95% CI 1.4–10.5). The mean time to tumour development was 22.6 days (95% CI 19.9–25.6 days) in the no treatment group and 50 days (95% CI 39.4–60.6 days) in the dexamethasone group (Mann-Whitney test, two-sided p-value=0.0005). The earliest tumour in the dexamethasone group developed 10 days after treatment ceased. Conclusion: Dexamethasone inhibits wound-induced, benign epidermal tumours in MEK1 transgenic mice. Tumours can occur after dexamethasone withdrawal. This anti-proliferative effect may be through suppression of the dermal inflammatory infiltrate. Further investigation will include the use of anti-inflammatory agents with a more specific activity profile. No significant financial relationships to disclose.

Activating mutations of the tyrosine kinase receptor FGFR3 are associated with benign skin tumors in mice and humans

Specific germline activating point mutations in the gene encoding the tyrosine kinase receptor FGFR3 (fibroblast growth factor receptor 3) result in autosomal dominant human skeletal dysplasias. The identification in multiple myeloma and in two epithelial cancers-bladder and cervical carcinomas-of somatic FGFR3 mutations identical to the germinal activating mutations found in skeletal dysplasias, together with functional studies, have suggested an oncogenic role for this receptor. Although acanthosis nigricans, a benign skin tumor, has been found in some syndromes associated with germinal activating mutations of FGFR3, the role of activated FGFR3 in the epidermis has never been investigated. Here, we targeted an activated receptor mutant (S249C FGFR3) to the basal cells of the epidermis of transgenic mice. Mice expressing the transgene developed benign epidermal tumors with no sign of malignancy. These skin lesions had features in common with acanthosis nigricans and other benign human skin tumors, including seborrheic keratosis, one of the most common benign epidermal tumors in humans. We therefore screened a series of 62 cases of seborrheic keratosis for FGFR3 mutations. A large proportion of these tumors (39%) harbored somatic activating FGFR3 mutations, identical to those associated with skeletal dysplasia syndromes and bladder and cervical neoplasms. Our findings directly implicate FGFR3 activation as a major cause of benign epidermal tumors in humans.

The mechanism of hyperpigmentation in seborrhoeic keratosis involves the high expression of endothelin-converting enzyme-1alpha and TNF-alpha, which stimulate secretion of endothelin 1.

Seborrhoeic keratosis (SK) is a benign epidermal tumour with increased pigmentation. We have recently demonstrated that increased secretion of endothelin (ET)-1, a strong keratinocyte-derived mitogen and melanogen for human melanocytes, is intrinsically involved in the hyperpigmentation mechanism of SK. To examine whether the increased ET secretion results from cytokines that induce ET production and/or from differences in the processing of ET that lead to its final active, secreted form. We used immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) to determine whether ET-inducing enzymes and/or cytokines are also highly expressed in SK. RT-PCR of mRNAs encoding interleukin (IL)-1alpha, tumour necrosis factor (TNF)-alpha and endothelin-converting enzyme (ECE)-1alpha demonstrated that there is an increased expression of TNF-alpha and ECE-1alpha mRNAs in SK, whereas the IL-1alpha transcript is rather downregulated in SK compared with that in perilesional normal epidermis. In parallel, immunohistochemical analysis of SK revealed marked immunostaining for TNF-alpha in basaloid cells at lower levels of the epidermis and in basal cells, and for ECE-1alpha in most basaloid and basal cells in comparison with their weak staining throughout the epidermis in perilesional normal controls. In contrast, immunostaining for IL-1alpha was almost negative in SK relative to distinctive staining throughout the epidermis in the perilesional normal controls. These findings suggest that the increased secretion of ET-1 leading to enhanced pigmentation in SK results from the co-ordinated increased expression of TNF-alpha and ECE-1alpha.

Tacalcitol, an Active Vitamin D3, Induces Nerve Growth Factor Production in Human Epidermal Keratinocytes

The human epidermal keratinocyte cell line K-TL-1, developed from a benign epidermal tumor, was cultured in the presence of the synthetic vitamin D₃ analogue tacalcitol [1α,24(R)-dihydroxyvitamin D₃] to assess the effects on the production of nerve growth factor (NGF). Confluent K-TL-1 cells were cultured with 10^–8M of tacalcitol. Supernatants and cell homogenates were collected and NGF concentrations were determined by enzyme-linked immunosorbent assay. The concentration of NGF in the supernatants of cultures treated with tacalcitol peaked within 24 h after the start of tacalcitol treatment and remained stable for 96 h. This NGF induction caused by tacalcitol was dose-dependent, showing an ED₅₀ between 10^–10 and 10^–9M. Induction of NGF mRNA expression by tacalcitol was also observed by RT-PCR, indicating that tacalcitol induced NGF expression through transcriptional activation. These results suggest that active vitamin D₃ could treat peripheral neuropathy by inducing NGF production in the skin.

Absence of human papillomavirus DNA in nongenital seborrheic keratosis.

Seborrheic keratosis (SK) is a benign epidermal tumor of unknown etiology. Because of its wart-like morphology, human papillomavirus (HPV) has been suggested as a possible causative agent. Viral involvement, however, has not been confirmed yet despite extensive research. The aim of this study was to evaluate the presence of HPV 6/11, 31, 33 DNA in nongenital SK. We analyzed 40 biopsy specimens taken from patients with nongenital SK using in situ polymerase chain reaction (PCR) and PCR with tissue extracts. The SK specimens (n=40), analyzed by in situ PCR, were negative for all HPV probes tested (types 6/11, 31, 33). Control slides (condyloma acuminatum, n=3) were positive for type 6/11, 31, and 33 HPV probes tested. Melasma samples (n=4), the negative controls, were consistently negative. No HPV DNA band was detected by PCR with the tissue extracts from paraffin-embedded SK samples, while condyloma acuminatum, the positive controls, showed DNA bands of the correct molecular weights. Our results show that HPV type 6/11, 31, and 33 cannot be recognized as causative agents for nongenital SK, which is in contrast to the previous studies. Further studies are required to reveal the presence of other types (more than 90) of HPV DNA.

Role of endothelin-1 in hyperpigmentation in seborrhoeic keratosis

Seborrhoeic keratosis (SK) is a benign epidermal tumour with a varying degree of pigmentation. We have recently demonstrated that endothelin-1 (ET-1) is a strong keratinocyte-derived mitogen and melanogen for human melanocytes in UVB-induced melanosis. To clarify the role of ET-1 in hyperpigmentation in SK, we have used immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) to see whether the production of ET-1 is accentuated in SK. Immunohistochemical analysis in SK (n = 7; acanthotic and deeply pigmented types) revealed marked immunostaining with anti-ET-1 in almost all basaloid and basal cells as compared with definite staining confined to basal cells in the perilesional normal controls. In parallel, RT-PCR of ET-1 mRNA demonstrated accentuated expression of ET-1 transcript in SK (n = 4) in comparison with that in the perilesional normal controls, accompanied by a similarly accentuated expression of tyrosinase mRNA. These findings suggest that ET-1 plays a part in the hyperpigmentation seen in SK.

Detection of apoptosis by in situ labeling in pilomatricoma.

Pilomatricoma is a benign epidermal appendage tumor with differentiation toward hair cortex cells. It is composed of varying percentages of basophilic cells, shadow cells, and transitional cells. Transitional cells seem to be apoptotic cells as evidenced by their morphological and ultrastructural characteristics. We investigated apoptosis in ten specimens of pilomatricoma by the transferase-mediated dUTP-biotin nick end labeling (TUNEL) technique. TUNEL-positive structures were detected in both transitional cell and amorphous debris zones, but not in either basophilic cell or shadow cell zones. In the transitional cell zone, apoptotic cells were found either in groups or bands, while in the amorphous debris zone, apoptotic bodies of varying sizes were seen diffusely. These findings indicate that transitional cells, due to the fact that they are dying cells, may not differentiate into the shadow cells. This view is supported by the facts that the transition of basophilic cells into the shadow cells is abrupt in some areas and that tumor cells, with or without ultrastructural characteristics of apoptosis, are found in the transitional cell zone. Furthermore, ultrastructural nuclear changes in shadow cells are different from those seen in apoptosis. Therefore, we propose that the name of transitional cells should be changed to "condensed cells." Although it has been conventionally though that basophilic cells in pilomatricoma differentiate directly and/or via transitional cells into shadow cells, we demonstrate that basophilic cells undergo two different processes. The first is differentiation directly into shadow cells, an the second is passage, via "condensed cells" (transitional cells), into the amorphous debris that results from tumor kinetics.

Strategy for identifying the gene encoding the DNA polymerase of molluscum contagiosum virus type 1.

Molluscum contagiosum virus (MCV) is a member of the family Poxviridae and pathogenic to humans. MCV causes benign epidermal tumors mainly in children and young adults and is a common pathogen in immunecompromised individuals. The viral DNA polymerase is the essential enzyme involved in the replication of the genome of DNA viruses. The identification and characterization of the gene encoding the DNA polymerase of molluscum contagiosum virus type 1 (MCV-1) was carried out by PCR technology and nucleotide sequence analysis. Computer-aided analysis of known amino acid sequences of DNA polymerases from two members of the poxvirus family revealed a high amino acid sequence homology of about 49.7% as detected between the DNA polymerases of vaccinia virus (genus Orthopoxvirus) and fowlpoxvirus (genus Avipoxvirus). Specific oligonucleotide primers were designed and synthesized according to the distinct conserved regions of amino acid sequences of the DNA polymerases in which the codon usage of the MCV-1 genome was considered. Using this technology a 228 bp DNA fragment was amplified and used as hybridization probe for identifying the corresponding gene of the MCV-1 genome. It was found that the PCR product was able to hybridize to the BamHI MCV-1 DNA fragment G (9.2 kbp, 0.284 to 0.332 map units). The nucleotide sequence of this particular region of the MCV-1 genome (7267 bp) between map coordinates 0.284 and 0.315 was determined. The analysis of the DNA sequences revealed the presence of 22 open reading frames (ORFs-1 to -22). ORF-13 (3012 bp; nucleotide positions 6624 to 3612) codes for a putative protein of a predicted size of 115 kDa (1004 aa) which shows 40.1% identity and 35% similarity to the amino acid sequences of the DNA polymerases of vaccinia, variola, and fowlpoxvirus. In addition significant homologies (30% to 55%) were found between the amino acid sequences of the ORFs 3, -5, -9, and -14 and the amino acid sequences of the E6R, E8R, E10R, and a 7.3 kDa protein of vaccinia and variola virus, respectively. Comparative analysis of the genomic positions of the loci of the detected viral genes including the DNA polymerases of MCV-1, vaccinia, and variola virus revealed a similar gene organization and arrangement.