Nucleolar organizer regions in Spitz nevi and malignant melanomas

Immunohistologic Evaluation of Putatively Mutant p53 Protein in Cutaneous Melanocytic Neoplasms

Mutations in the p53 tumor suppressor gene, located at chromosomal locus 17pI3, are the most commonly seen genetic alterations found in human malignancies. Their role in the pathogenesis of malignant melanoma is thought to be limited, although variable results have been reported in reference to immunoreactivity for putatively mutant p53 protein (mp53) in melanocytic lesions in general. In that light, the authors undertook an immunohistologic evaluation of 256 well-characterized tumors in that category, including common nevi (CN; n=73); Spitz nevi (SN; n=40); nodular melanomas (NMMs; n=32), superficial spreading melanomas (SMMs; n=65); lentigo maligna melanomas (LMMs; n=23); and melanomas arising in preexisting nevi (MANs; n=23). One hundred cells were counted manually in randomly selected high-power microscopic fields, in regard to nuclear labeling for mp53. Results were recorded semiquantitatively, as negative, positive (1-4% of tumor cells); and positive (>5% of tumor cells). No examples of CN or SN demonstrated any immunoreactivity whatever for mp53, whereas 105 of 143 melanomas (73%) did so. However, an mp53 index of >50% was seen in only 29% of the latter lesions. NMMs were most often mp53-positive and showed the highest numerical level of nuclear labeling, followed in respective order by SMMs, and LMMs/MANs. These results suggest that negative mp53-immunostaining cannot be equated with the diagnostic interpretation of a benign melanocytic neoplasm, because 27% of melanomas also failed to label for that determinant. However, the presence of mp53-immunolabeling in a melanocytic proliferation-even if at low levels-should conversely prompt careful consideration of melanoma as the favored diagnosis in the confined setting of morphologically difficult cases, inasmuch as no example of CN or SN in this series had that characteristic.

The evaluation of argyrophilic nucleolar organizing region proteins in fine-needle aspiration samples of thyroid

Argyrophilic nucleolar organizing region associated proteins (AgNORs) have been shown to be of interest in a variety of different diseases including thyroid disorders. Our aim was to distinguish benign thyroid lesions from papillary thyroid carcinoma (PTC) via AgNOR count and with a new approach, via AgNOR surface area/total nuclear surface area (NORa/TNa) proportions in the nuclei on fine-needle aspiration (FNA) materials. Thirty patients (eight men and 22 women) whose FNA was compatible with benign lesion and 26 patients (eight men and 18 women) whose FNA was compatible with PTC were included in the study. Fine-needle aspiration materials were stained for AgNOR detection according to a specific protocol. One hundred nuclei per individual have been evaluated, and AgNOR number and NORa/TNa proportions of individual cells were measured and calculated by using a computer program. Patients with PTC had significantly (p<0.001) higher AgNOR count (4.6 ± 1.2%) than in the patients with benign lesions (2.0 ± 0.5%). Additionally, patients with PTC had significantly (p<0.001) higher NORa/TNa (13.4 ± 2.4) than in the patients with benign lesion (5.7 ± 1.0). Modified method of AgNOR staining is an easy and reliable method for evaluating proliferation activity of cells in malignant and benign thyroid lesions and it may contribute to routine cytopathology in inconclusive situations.

The immunohistochemical profile of Spitz nevi and conventional (non-Spitzoid) melanomas: a baseline study

Several isolated markers have been proposed to aid in differential diagnostic of difficult melanocytic lesions, albeit none has been shown to be definitive in differentiating Spitz nevus from melanoma. This study proposes a wide panel of 22 markers having important functions in different biological functions (cell cycle, apoptosis, DNA repair proteins and membranous receptors) to provide a combination of proteins associated with either benign or malignant phenotype. Using tissue microarrays, we compared protein expression profiles in 28 typical Spitz nevi and 62 primary vertical growth phase non-spitzoid melanomas. Most of the significant differences were linked to cell-cycle deregulation such as overexpression of cyclin D1 and p21 in Spitz nevi compared with non-spitzoid melanomas (74 vs 16% and 91 vs 27%, respectively) and mitotic rate including Ki-67, highly expressed in deep areas of non-spitzoid melanomas (37%), whereas it is not expressed in Spitz nevi (0%), topoisomerase IIalpha (79% in non-spitzoid melanomas vs 15% in Spitz nevi) and nuclear survivin (69% in melanomas vs 0% in Spitz nevi). A combination of biological markers differentially expressed in Spitz nevi from non-spitzoid melanomas is defined, thus providing a potential tool for histopathological differential diagnostic between Spitz nevus and melanoma. Nevertheless, more studies including atypical Spitz nevi and spitzoid melanomas are necessary to further establish a reliable panel to differentiate among difficult cases.

Nucleolar organizer regions (AgNOR) and subepithelial vascularization as field cancerization markers in oral mucosa biopsies of alcoholic and smoking patients

OBJECTIVE

The aim of this study was to show that variations in nucleolar organizer regions (AgNOR) and the increase in subepithelial vascularization could reveal changes related to markers of field cancerization in alcoholic and smoking patients who have not yet expressed clinical or histological malignant lesions.

STUDY DESIGN

Quantitative variations in epithelial AgNOR and in the vascularization of the underlying connective tissue were assessed by image analysis in histologically normal biopsy specimens from alcohol drinkers and smoking patients (DS). AgNORs were evidenced by silver staining and vessel walls were labeled by immunohistochemical demonstration of the CD34 antigen. Samples of oral mucosa of nonalcoholic, nonsmoking patients (NDS) obtained during surgical procedures served as controls. Eight parameters related to number, volume, and shape of nuclei and AgNORs, and 4 parameters related to number and diameter of vascular sections were evaluated. Differences between DS and NDS groups were statistically evaluated by means of ANOVA test and posterior Bonferroni comparisons.

RESULTS

The morphometric analysis revealed more irregular-shaped AgNORs in the superficial and suprabasal layers of the oral mucosa of DS patients. The suprabasal layers also exhibited a significantly larger number of AgNORs. The normal oral mucosa of DS patients exhibited a greater vascular density, with predominance of small-caliber blood vessels underlying the basement membrane.

CONCLUSION

The variations in AgNOR and epithelial vascularization would be practical biomarkers to evaluate changes underlying the augmented risk of cancerization in oral mucosa.

Preventing liver metastasis by resecting the primary pancreatic carcinoma at an early stage of intrapancreatic transplantation in hamsters

PURPOSE

To determine whether early primary pancreatic tumor resection can prevent liver metastases of intrapancreatic transplantation in a hamster model.

METHODS

Cells from the PGHAM-1 cell line were transplanted into the pancreases of 30 Syrian golden hamsters. A suspension of 5 x 10(6) cells was injected into the splenic lobe of each pancreas. The primary pancreatic tumor was resected in 15 of the hamsters 10 days after transplantation (resection group). Fifteen other animals with transplantation but without resection served as controls (control group). All hamsters were killed 21 days after transplantation. The primary pancreatic tumors were measured for size and volume and examined histologically and immunohistologically for angiogenesis and tumor proliferation.

RESULTS

In the resection group, small pancreatic tumors 4.7 +/- 0.94 mm in diameter were found and resected 10 days after transplantation. Neither pancreatic tumors nor liver metastases were found in the resection group at the end of the experiment. All animals in the control group had pancreatic tumors 12.3 +/- 3.29 mm in size, and 11 of 15 (73.3%) had liver metastases. The primary pancreatic tumors in the group with liver metastasis were significantly larger in diameter and volume than those in this group without liver metastasis (p<0.01). In the control group, proliferation of the primary pancreatic tumor, evaluated according to argyrophilic nucleolar organizer region, showed no differences within the pancreatic tumor group. On the other hand, the microvessel density of pancreatic tumors with liver metastases was significantly higher than that of tumors without liver metastases.

CONCLUSIONS

Our results suggest that 10 days after transplantation, the pancreatic tumors were small in size and volume and ready to proliferate but not yet ready to begin metastasizing through angiogenesis. This is one reason why early resection of the primary tumor prevents liver metastasis.

BRAF and NRAS mutations in spitzoid melanocytic lesions

BRAF mutations are common events in a variety of melanocytic nevi and primary cutaneous melanomas. We have previously found BRAF mutations in 82% of nevi, consisting of congenital, common acquired and dysplastic types, and 33% of primary cutaneous melanomas other than the spitzoid type, similar to other published reports. A small number of studies have evaluated Spitz nevi and have failed to detect any lesions possessing a BRAF mutation. Only one study included categories of atypical Spitz nevus and borderline lesions suspected to be spitzoid melanomas, along with classic Spitz nevi and spitzoid melanomas. We examined a spectrum of spitzoid lesions that included 48 Spitz nevi, some with atypical features, seven atypical (borderline) Spitz tumors, and 13 spitzoid melanomas. BRAF mutations were detected in 12 of 68 spitzoid lesions, of which two were spitzoid melanomas and 10 were Spitz nevi. Five of the 10 Spitz nevi with BRAF mutations were altered by more than usual cytologic atypia and/or architectural atypia overlapping with dysplastic nevi, or irritation/inflammation; one desmoplastic Spitz nevus had a BRAF mutation. These results indicate that a small subset of Spitz nevi, some with atypical histologic features, possess BRAF mutations. Therefore, the BRAF mutational status does not separate all Spitz nevi from spitzoid melanomas and non-Spitz types of melanocytic proliferations, contrary to previous reports.

Re-expression of reduced VEGF activity in liver metastases of experimental pancreatic cancer

PURPOSE

Vascular endothelial growth factor (VEGF) is thought to play a crucial role in the process of cancer growth and metastasis. In this study, the expression of VEGF in liver metastases of pancreatic cancer was investigated using an established hamster model.

METHODS

Pancreatic cancer cells (PGHAM-1, 1 x 10(6)) derived from N-nitrosobis (2-oxopropyl) amine (BOP)-induced pancreatic tumors in Syrian golden hamsters were transplanted into the pancreas of female hamsters. All hamsters were sacrificed at 21 days after transplantation and used for the histopathological examination of pancreatic and metastatic lesions (primary transplantation model). The metastatic liver tumors were minced with scissors and 1 mm(3) tumors were retransplanted into the pancreas of a second hamster. All hamsters were sacrificed 21 days after retransplantation, and the pancreatic tumors were removed (back transplantation model). Immunohistochemical analyses using antibody against VEGF were performed for all pancreatic and liver tumors. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to examine the expression of VEGF mRNA in the tumors. In addition, we investigated the proliferation of each tumor using Ag-NOR staining.

RESULTS

In the primary transplantation models, VEGF expression in the pancreatic tumors was positive, but that in the liver metastases was only weakly positive or negative. On the other hand, VEGF expression in the pancreatic tumors that had developed from the retransplantation of the liver tumors (back transplantation model) was strongly positive. VEGF mRNA was expressed in the pancreatic tumors of both primary and back transplantation models. In the metastatic liver tumors of the primary transplantation model, VEGF mRNA was expressed in all cases, although the immunohistochemical staining pattern was weakly positive or negative. Similarly, in the metastatic liver tumor of the back transplantation model, VEGF mRNA was expressed in all cases, although the immunohistochemical staining pattern was weakly positive or negative. No significant differences in Ag-NOR scores were found between the models.

CONCLUSION

Our results suggest that VEGF expression usually occurs in PGHAM-1 cells but that VEGF expression is reduced during the process of liver metastasis and revived by retransplantation. Thus, the interrelationship between cancer cells and the organ environment might play an important role in VEGF expression.

Spitz nevi and atypical Spitz nevi/tumors: a histologic and immunohistochemical analysis

A subset of Spitz nevi poses substantial diagnostic difficulty, even among experts, due to its resemblance to malignant melanoma. These lesions are termed atypical Spitz nevi/tumors and there is currently a lack of objective criteria for predicting their biologic behavior. We compared the expression of Ki-67, p21, and fatty acid synthase by immunohistochemistry in 10 atypical Spitz nevi, 28 typical Spitz nevi, 19 compound melanocytic nevi and 18 invasive malignant melanomas. There was a progressive increase in fatty acid synthase cytoplasmic expression with statistically significant differences observed between Spitz nevi and atypical Spitz nevi (P=0.003) and between atypical Spitz nevi and malignant melanoma (P<0.050). Ki-67 nuclear staining was lower in both typical and atypical forms of Spitz lesions than in malignant melanoma (P<0.001). The degree of P21 nuclear expression in atypical Spitz nevi was not significantly different than in Spitz nevi, but was significantly greater than expression in conventional nevi and approached significance after multiple comparisons corrections for malignant melanoma. Thus, a high level of P21 expression makes a tumor more likely to be a typical or atypical Spitz nevus than a malignant melanoma, especially when coupled with a low Ki-67 index and weak expression of fatty acid synthase. These immunohistochemical observations support the concept that atypical Spitz nevi are distinct lesions of borderline biologic behavior residing between Spitz nevi and malignant melanoma. The study also compared a large array of histologic features of 16 cases of typical Spitz nevi in children with 12 typical Spitz nevi in adults. The adult lesions were significantly more likely to be intradermal and to display dermal fibroplasia, but were histologically similar to their pediatric counterparts in all other respects.

Local invasiveness of ameloblastoma. Role played by matrix metalloproteinases and proliferative activity

AIMS

Ameloblastoma is an odontogenic neoplasm characterized by local invasiveness and recurrence. In this study we analysed the role played by matrix metalloproteinases (MMPs) in the local invasiveness of ameloblastoma. We also attempted to establish a relationship between the presence of MMPs and the proliferative activity of ameloblastoma cells.

METHODS AND RESULTS

Immunohistochemistry was carried out to detect different MMPs in formalin-fixed paraffin-embedded samples of human ameloblastoma. Immunohistochemistry, however, does not establish whether a given MMP is latent or active. To address this point, we carried out biochemical methods, namely zymography and Western blotting. Our results showed expression of latent and active forms of MMPs 1, 2 and 9 in ameloblastoma. These enzymes may digest bone matrix and release mitogenic factors, which would increase tumour proliferation. This possibility prompted us to study the proliferation of ameloblastoma cells located in close proximity to bone. Silver-stained nucleolar organizer region morphometry revealed that ameloblastoma cells in the vicinity of bone show increased proliferation, when compared with controls.

CONCLUSIONS

Our results suggest an interdependent mechanism involving MMPs and proliferation of ameloblastoma cells, which may contribute to the local invasiveness of this tumour.

Argyrophilic staining of nucleolar organizer region count and morphometry in benign and malignant melanocytic lesions

Differentiation between malignant melanomas (MMs) and benign nevi based on histologic features can sometimes be difficult. This study evaluated the diagnostic effectiveness of argyrophilic staining of nucleolar organizer regions (AgNORs) in separating benign nevi from MMs by assessing 27 compound nevi (CN), 20 dysplastic nevi (DN), 10 Spitz nevi (SN), and 24 MMs. Both AgNOR count and morphology variables were measured from the superficial, middle, and deep zones of the lesions using video image analysis. Malignant melanomas had a significantly greater AgNOR number per nucleus, mean AgNOR area per nucleus, and variation in AgNOR area per nucleus compared with all types of benign nevi (p < 0.05). In multivariate discriminant analysis using a combination of four AgNOR counts and morphometric parameters, all CN and DN, 8 of 10 SN, and 23 of 24 MMs could be correctly classified as benign or malignant. The results suggest that both AgNOR count and morphology help to separate benign and malignant melanocytic lesions and that the combination of both sets of parameters improves their discriminating ability.

Antitumor effect of a new selective matrix metalloproteinase inhibitor, MMI-166, on experimental pancreatic cancer

The antitumor effect of a new matrix metalloproteinase inhibitor, MMI-166, which is a selective inhibitor of MMP-2 and -9, was examined in the hamster pancreatic cancer cell line PGHAM-1. In vitro, MMI-166 inhibited the gelatinase activity of MMP-2 and -9 derived from PGHAM-1 cells, and dose-dependently inhibited invasion of PGHAM-1 through a basement membrane-like barrier. MMI-166 showed no apparent cytotoxicity to PGHAM-1 cells in culture at 100 microgram/ml. MMI-166 (200 mg/kg) or vehicle were administered orally, once daily, from day 1 until day 21 after implantation in the orthotopic implantation model of PGHAM-1. MMI-166 significantly reduced the incidence of liver surface metastasis from 66.7% to 20.0%, and it reduced the number of liver surface metastases per animal from 6.17 to 2.00, but this reduction was not significant. MMI-166 significantly reduced the volume of pancreatic tumors from 718.3 +/- 220.0 mm(3) to 222.8 +/- 85.4 mm(3). Treatment of pancreatic tumors with MMI-166 caused a significant reduction in the microvessel density from 37.90 +/- 10.18/mm(2) to 16.16 +/- 3.15/mm(2) and a significant increase in apoptotic index from 1.75 +/- 0.41% to 3.96 +/- 0.38%, but there was no significant difference between tumor cell proliferation in the MMI-166-group and the control group. These results showed that selective MMP inhibition could limit both cancer spread and angiogenesis in pancreatic cancer. The selective MMP-2 and -9 inhibitor MMI-166 may be of therapeutic use in the treatment of pancreatic cancer because of its inhibitory effect on invasion and angiogenesis.

Effect of angiostatin on liver metastasis of pancreatic cancer in hamsters

The liver is the most common site of metastasis in pancreatic cancer, and there are no promising strategies to treat it. Angiostatin, a kringle-containing fragment of plasminogen, is a potent inhibitor of angiogenesis. The effect of angiostatin on liver metastasis in pancreatic cancer was investigated by using our established hamster model of liver metastasis. Pancreatic cancer cells (PGHAM-1, 1 x 10(6)) derived from N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic tumor in Syrian golden hamsters were transplanted into the spleen of female hamsters, and the animals were subcutaneously injected with angiostatin and saline. Subsequently, the macroscopic appearance of liver surface metastases was evaluated. In addition, histological sections of the liver metastases were analyzed for neovascularization, proliferation, and apoptosis on the basis of von Willebrand factor, argyrophilic nucleolar organizer region (Ag-NOR), and TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining, respectively. The results showed significant tumor growth retardation and inhibition of angiogenesis in metastatic liver tumors in response to treatment with angiostatin. Moreover, the metastases remained in a nearly dormant state due to a balance between apoptosis and proliferation of the tumor, with no detectable side effects. This is the first experimental trial of angiostatin on pancreatic cancer and liver metastasis. The results suggest that angiostatin therapy could be effective against liver metastases of pancreatic cancer.

AgNOR are sensitive markers of radiation lesions in squamous epithelia

The possibility of detection of incipient cellular alterations is central to early diagnosis and to clinician's capacity to discriminate between samples that appear similar on routine preparations. We examined the value of silver-stained nucleolar organizer regions (AgNOR) in detecting radio-induced alterations in a model of squamous epithelium biologically similar to oral mucosa. Morphometry of AgNOR has been proven to be of value in the detection of incipient cellular alterations. This method allows for the quantitative evaluation of lesions induced by high doses of radiation long before they become apparent in routine preparations. We herein examine the capacity of AgNOR to reveal the response to low doses of radiation, closer to the therapeutic or accidental dose to which the epithelium of oral mucosa may be exposed.

Spitz nevus or melanoma?

Spitz nevi are benign melanocytic neoplasms of children and young adults that can be exceedingly difficult to distinguish from malignant melanomas. Although a nearly definite diagnosis can be made in most cases, the histological distinction between Spitz nevi and melanomas is equivocal in about 6% to 8% of cases. In those cases, and perhaps even with presumed benign Spitz nevi, clear surgical margins are desirable. The most helpful differentiating features of Spitz nevi are patient age, sharp demarcation, symmetry, maturation of melanocytes at the base, and epithelial hyperplasia. None of these criteria are completely reliable, and multiple other criteria must be considered as well.

Evaluation of argyrophilic nucleolar organizer regions in tongue squamous cell carcinomas

Using a silver staining technique, argyrophilic nucleolar organizer regions (AgNORs) were studied on the biopsy specimens taken from 67 tongue squamous cell carcinomas (SCCs), and the relations of the results of AgNORs to the clinicopathological findings, to the labelling indices of proliferating cell nuclear antigen (PCNA LI), and to the outcomes of the disease were investigated. The mean numbers of AgNORs per cell were 1.67 +/- 0.19 (n = 27) in the control squamous epithelia and 3.58 +/- 1.15 (n = 67) in the tongue SCCs, respectively, and a significant difference was found between the two groups (P < 0.0001). Concerning the clinicopathological findings, the mean numbers of AgNORs in the progressive cases (T3, T4), in the factor N-positive groups (N1, N2), and in the advanced stages (stages III, IV) were statistically higher than those in T1, T2, N0, and earlier stage (stages I, II) tumours, respectively. Similarly, a higher value of the AgNOR count was present in the histological grade III or diffuse invasive tumour. There was also a directly significant correlation between the AgNOR counts and the labelling indices of PCNA (r = 0.53, P < 0.0001). Concerning the outcome of the disease, the mean numbers of AgNORs were higher in the group with local recurrence or with lymph-node metastasis. A lower rate of 5 years' survival was found in the high value group (63.5%) of AgNORs compared with that of the low value group (86.0%), with a significant difference between the two groups (P < 0.05). The results suggest that AgNORs may reflect the degree of malignancy and cellular proliferation in tongue SCCs.

Synergistic effects of hyperthermia in preoperative radiochemotherapy for rectal carcinoma

PURPOSE

We investigated the effectiveness of hyperthermia added to preoperative radiation and chemotherapy for the treatment of rectal carcinoma.

METHODS

Forty-one patients receiving preoperative radiation were divided into two groups, Group A (20 patients; receiving radiation, hyperthermia, and chemotherapy) and Group B (21 patients, receiving no hyperthermia). Total dose of radiation was 40.5 Gy. Hyperthermia was administered using 8 MHz of radiofrequency. Rectal temperature reached 42 degrees C. A total dose of 3,400 mg of 5-fluorouracil given by suppository was used as the chemotherapeutic agent. Effect of the preoperative treatment was assessed by tumor reduction on barium enema, histologic findings of the resected specimens, area measurement of the residual cancer tissue, and by silver-staining nucleolar organizer region (AgNOR) score.

RESULTS

Tumor reduction on barium enema was significantly greater in Group A than in Group B (P < 0.01). Excluding two cases of mucinous carcinoma because a large acellular mucinous accumulation added materially to the cancerous area, the ratio of residual cancer area to total lesion size in Group A was significantly smaller than in Group B (P < 0.05). AgNOR score of the resected tumor tended to be smaller in Group A than in Group B.

CONCLUSION

Addition of hyperthermia resulted in a greater degree of tumor necrosis and was considered to be useful as a preoperative treatment for rectal carcinoma.

Morphometric study of nucleolar organiser regions in ameloblastoma and basal cell carcinoma

Ameloblastoma and basal cell carcinoma share histological similarities. Morphometric analysis of nucleolar organiser regions (NORs) from ameloblastoma and basal cell carcinoma (BCC) was carried out by silver (Ag) staining. Mean counts were lower in ameloblastoma (1.652 +/- 0.032) compared to those in BCC (2.354 +/- 0.054). Ameloblastoma presented one or two NORs per nucleus, in a narrow distribution (one to four NORs per nucleus). In contrast, BCC exhibited two or three NORs per nucleus, in a broad distribution (one to six NORs per nucleus). Perimeter and area measurements of AgNOR dots yielded significantly higher mean values for ameloblastoma. Our data suggest that most BCC cells are in mitosis, showing small and numerous NORs in each nucleus, while ameloblastoma cells are in interphase, showing one or two large NORs in each nucleus. Although ameloblastoma and BCC are neoplasms with similar growth patterns, they have cell populations with statistically significant differences in AgNOR patterns.

Clinical study of the relationship between cytological behavior and postoperative prognosis in colorectal cancer cases with special reference to nuclear DNA content and nucleolar organizer regions

BACKGROUND

We studied the usefulness of nuclear DNA patterns and argyrophylic nucleolar organizer regions (AgNORs) for evaluating the malignant potential of colorectal cancers, which is increasingly being regarded as important in predicting patients' prognosis and for their appropriate postoperative management.

METHODS

We measured these two factors in curatively resected specimens of 91 colorectal cancer cases, which were followed up for 1,549 +/- 788 days postoperatively. Ploidy pattern was either diploid or aneuploid, and AgNORs score was either low (LS) or high (HS). Thus, we classified our cases into Group I (diploid, LS). Group II (aneuploid, LS), Group III (diploid, HS), and Group IV (aneuploid, HS). Postoperative survival curves in the cases belonging to these groups were analyzed.

RESULTS

Survival rates in Groups I and II were significantly higher than those in Group IV. Correlation between subgroups and clinicopathological factors such as average age, histologic type, depth of invasion, and histologic stage were observed. Incidence of lymph node metastasis at the time of operation and that of postoperative recurrence were higher in group IV than that in groups I and II.

CONCLUSIONS

Measurement of DNA ploidy patterns and AgNORs score were found to be useful in evaluating malignant potential of colorectal cancers.

Nucleolar organizer regions in parosteal and central osteosarcomas

Silver stained nucleolar organizer regions (AgNOR) have revealed differences in the biological behavior of certain entities. This study involves a morphometric analysis of AgNOR in 6 central, classic osteosarcomas and 6 parosteal osteosarcomas. There was a statistically significant difference in the number of AgNOR per nucleus between central and parosteal osteosarcomas. Single AgNOR volume was smaller in central osteosarcomas as compared to parosteal osteosarcomas. However, this difference did not reach statistical significance. The parameter AgNOR number per nucleus revealed a cut off value such that 100% of central osteosarcoma cases lay above this value and 100% of parosteal osteosarcoma cases lay below this value. AgNOR demonstration involves a simple technique which can be performed on formalin fixed, paraffin embedded file material. Thus, it may be prudent to routinely assess AgNOR as a contributor to the determination of the pathophysiology of osteosarcomas.

Recurrence of meningiomas versus proliferating cell nuclear antigen (PCNA) positivity and AgNOR counting

Meningiomas have a wide range of biological potential and clinical behaviour. Histological findings are helpful in recognizing the malignant potential but often fail to correlate with clinical behaviour. This study attempts to correlate the silver nucleolar organizer regions (AgNORs) and proliferating cell nuclear antigen (PCNA) with clinicopathological features of biological activity. Thirty-four completely resected meningiomas were classified as benign [19], atypical [6] and malignant [9]. Forty-eight initial and recurrent tumour materials were investigated for staining of AgNORs and immunohistochemistry using monoclonal antibodies against PCNA (clone 19A2 and PC10). There were no difference between the recurrent and non-recurrent cases with regards to AgNOR, PC10 and 19A2 values. Also, no significant difference was found between the primary and recurrent tumours. Both PC10 and 19A2 labelling indices (LI) showed a significant difference between benign and malignant meningiomas. The 19A2 LI was 0.56 +/- 0.21 in benign and 2.45 +/- 16 in atypical meningiomas. The 19 A2 counts showed significant difference between benign and atypical tumours but PC10 values failed to show such a correlation AgNOR and PCNA indices were not found to be useful in predicting recurrences compared to the surgical procedure and histopathological criteria.

AgNOR mark epithelial foci in malignant transformation in hamster cheek pouch carcinogenesis

Hamster cheek pouch mucosa is an accepted model of oral carcinogenesis. We herein examined the value of morphometric evaluation of silver-stained nucleolar organizer regions (AgNOR) in the detection of epithelial foci in malignant transformation following dimethyl-1,2-benzanthracene-induced carcinogenesis of hamster cheek pouch. AgNOR-related parameters were analyzed at different stages of the process of carcinogenesis (control epithelium, epithelium with no unusual microscopic features, "dysplastic" epithelium, exophytic and endophytic carcinomas). Morphometric evaluation of AgNOR revealed incipient cellular alterations which were not evident in routine preparations and contributed to the characterization of different stages of carcinogenesis in this model.

Evaluation of three different AgNOR counting methods in advanced carcinoma of the prostate

We applied the silver staining of nucleolar organizer regions (AgNOR) technique to the pretreatment biopsies of 50 cases of advanced prostate cancer. Three different counting methods were utilized in the enumeration of AgNORs. All methods yielded statistically significant differences of mean AgNOR counts of groups defined by high and low WHO, and by Gleason grades. However, there was overlap among groups, and further analysis of counts by grouping of patients according to their stage, response to treatment, and prognosis was not conclusive. Replicate counts were performed in 10 cases. While intraobserver reproducibility was high by all methods, only the second counting method yielded nonsignificant interobserver variability. There was a significant intratumoral heterogeneity of AgNOR scores. Lack of technical standardization, low reproducibility, and lack of correlation with prognosis limit the use of AgNOR counts in advanced carcinoma of the prostate.

Comparison of argyrophilic nucleolar organizer regions (AgNORs) and mitotic index in distinguishing benign from malignant canine smooth muscle tumors and in separating inflammatory hyperplasia from neoplastic lesions of the urinary bladder mucosa

Staining for argyrophilic nucleolar organizer regions (AgNORs) has proven useful in differentiating recurrent or malignant neoplasms from less aggressive or benign ones. We applied this stain to benign and malignant smooth muscle tumors and to hyperplastic and carcinomatous lesions in the urinary bladder of dogs in an effort to determine its utility in diagnostic situations. The stain was simply performed, and the results were repeatable for different staining intervals and between staining batches. For smooth muscle tumors, enumeration of AgNORs in 100 nuclei was about as efficient as mitotic index in correctly categorizing histologically benign and malignant neoplasms. The mean number of AgNORs/100 nuclei for leiomyomas was significantly less than that obtained for leiomyosarcomas and significantly greater than that obtained for normal smooth muscle. Counts for smooth muscle tumors correlated with the mitotic indexes. Counts by an individual observer were repeated without introducing significant variation, but there was variability between observers, particularly in AgNOR counts for leiomyosarcomas. AgNORs were not useful in separating hyperplastic or polypoid cystitis from transitional cell carcinoma, misclassifying both. Mean AgNOR counts for these 2 conditions did not differ at the 5% level of significance; mitotic index was more efficient at separating the 2 conditions. There was no correlation between mitotic index and AgNOR in urinary tract mucosal specimens. This easily prepared stain may be useful in separating benign and malignant smooth muscle tumors, although AgNORs were less contributory to diagnosing mucosal lesions of the urinary bladder of dogs.

Prognostic significance of nucleolar organizer regions (NORS) in malignant melanoma

Nucleolar organizer regions (NORs) are loops of ribosomal DNA (rDNA) in the nucleolus and are associated with acidic proteins. They are seen in routinely processed paraffin sections by using a one-step colloidal silver (Ag) staining method; they appear as black dots termed "AgNORs". The quantitative assay of AgNORs has been used to differentiate benign from malignant neoplasms. Melanocytic lesions differ significantly in AgNOR counts between malignant melanoma and nevi. However, conflicting results have been reported as to AgNORs' prognostic value in melanoma. A recent study showed AgNOR counts to be a more accurate prognostic indicator than Breslow's thickness. In this study, we counted the AgNORs in 26 patients with primary cutaneous melanomas (CMM) between 2.0 mm and 2.5 mm thick. Of these, 14 are alive without disease (AN) at 5 years after diagnosis (group 1) and 12 are dead of disease (DD) in less than 5 years (group 2). The AgNORs were scored in 30 nuclei per tumor, and the means were calculated. For group 1, the mean number of AgNORs per nucleus was 6.88, ranging from 3.73 to 12.70. For group 2, the mean number was 6.97, ranging from 3.63 to 11.67. Statistical analysis using analysis of variance (ANOVA) showed no significant difference between the groups (p = 0.33). In our study, AgNOR counts did not prove to be of prognostic value in malignant melanoma.

The argyrophilic nucleolar organizer regions in ductal carcinoma in situ of the breast. The significance of ploidy and proliferative activity analysis using this silver staining technique

BACKGROUND

Two interphase argyrophilic nucleolar organizer region (AgNOR) counts have been correlated with ploidy and proliferative activity in patients with ductal carcinoma in situ (DCIS) of the breast. The first is the mean number of AgNORs (mAgNOR); it reflects ploidy. The second is the percentage of nuclei with greater than or equal to five AgNORs/nucleus (pAgNOR); it correlates with proliferative activity. DCIS of the breast is a heterogeneous group of lesions that is not associated uniformly with invasive ductal carcinoma. A significant number of patients with DCIS will, however, progress to invasive ductal carcinoma. Factors identifying the invasive potential of DCIS in these patients have not been defined clearly. The authors postulated that pAgNOR in DCIS may predict the invasive potential of these lesions.

METHODS

The authors studied 86 cases of DCIS of the breast by the AgNOR silver stain using the two above-mentioned counts.

RESULTS

There were 54 comedo and 32 noncomedo DCIS cases. Forty-one cases (47%) were associated with invasive ductal carcinoma. Thirty cases of comedo DCIS (55%) showed mAgNOR counts suggestive of aneuploidy (> or = 2.4/nucleus), whereas only seven cases of noncomedo DCIS (22%) showed such counts (P = 0.001). Cases associated with invasion had higher incidence of aneuploid mAgNOR counts (P = 0.0003). The pAgNOR counts in comedo DCIS ranged from 1% to 36% (median, 11%), whereas in noncomedo DCIS pAgNOR counts ranged from 0% to 22% (median, 7%) (P = 0.007). The 41 cases associated with invasion had pAgNOR counts ranging from 3% to 36% (median, 12%), whereas those not associated with invasion had pAgNOR counts ranging from 0% to 24% (median, 5%) (P = 0.000001). This difference was irrespective of the type of DCIS or mAgNOR counts.

CONCLUSIONS

Comedo DCIS of the breast may show a higher incidence of aneuploidy and increased proliferative activity and invasive ductal carcinoma than does noncomedo DCIS. Ploidy and proliferative activity, measured by AgNOR staining in DCIS, may have a significant predictive value in identifying the invasive potential of these lesions.

Nucleolar organizer regions as a marker of incipient transformation in a model of experimental carcinogenesis

Nucleolar organizer regions stained selectively with a silver colloid technique (AgNOR) were evaluated during the process of tumour promotion in the skin of mice. Tumour promotion and control skin samples were processed for identification of AgNOR by light microscopy and submitted to a morphometric study of the following AgNOR-related variables: nuclear area (V.NUC); AgNOR number per nucleus (N.NOR); single AgNOR area (V.NOR); total AgNOR area per nucleus (TV.NOR) and proportion of nucleus occupied by AgNOR (TV.NOR/V.NUC). N.NOR exhibited significant differences between control and tumour tissue, but in the promotion period, N.NOR did not exhibit a significant rise until week 24. V.NOR and TV.NOR rose significantly as early as 2 weeks after the onset of promotion when the cells fail to exhibit unusual microscopic features. The significant increase in AgNOR material at the beginning of the promotion period reveals the potential value of the variables assessed in the early quantitative evaluation of cellular alterations which could be linked to the probability of tumour development. Rise in AgNOR material would indicate transcriptional activation leading to an increase in protein synthesis and, ultimately, to the expression of an altered phenotype.

Nucleolar organizer regions in lining epithelium adjacent to squamous cell carcinoma of human oral mucosa

BACKGROUND

The value of silver staining of nucleolar organizer regions (AgNOR) counts as a diagnostic aid has been reported for several neoplastic entities. Previous studies have proved the value of the morphometric evaluation of AgNOR in the detection of incipient cellular alterations.

METHODS

A morphometric analysis of AgNORs was performed in oral mucosa epithelium adjacent to squamous cell carcinoma compared with normal mucosa epithelium and the carcinomatous parenchyma.

RESULTS

Highly statistically significant differences in all 5 AgNOR-related parameters assessed were found between normal mucosa and mucosa adjacent to cancer. Conversely, the corresponding nuclear parameters failed to exhibit significant differences. The parameter AgNOR contour index plotted for individual cases affords a cutoff value that could prove useful in identifying epithelia at early stages of transformation.

CONCLUSIONS

AgNOR evidenced significant variations in epithelium adjacent to oral squamous cell carcinoma, which did not exhibit morphologic signs of atypia. Based on this study, AgNOR would be a quantitative, discriminative aid, easy to monitor in a pathology laboratory, in detecting incipient cellular alterations. These findings contribute to the issue of early diagnosis and to the knowledge of tumoral growth.

The value of the AgNOR staining method in identifying carcinoma in situ testis

An early and reliable diagnosis is necessary in order to have the chance of a curative therapy of Carcinoma in situ testis (Cis). Forty-six testicular biopsies were investigated to assess the value of the AgNOR staining method in comparison to placental alkaline phosphatase (PLAP) immunostaining. Both methods provided corresponding results and identical tumor cells were recognized in serial sections. The mean AgNOR counts per nucleus were 26.86 (19-52, SD: 2.68) for CIS cells, 8.18 (5-14, SD: 2.20) for spermatogonia and 12.96 (9-18, SD: 2.44) for Sertoli cells, without the counts overlapping within these three groups. Even single CIS cells are easily and reliably recognizable by their typical AgNOR pattern and their high AgNOR count per nucleus. The independent estimation of 9 testicular biopsies with the AgNOR staining method and the PLAP immunostaining correspondingly revealed 7 biopsies with CIS. Two biopsies lacked tumor cells. The AgNOR staining method can be recommended as an additional diagnostic tool in identifying CIS, because of the short and convenient staining procedure, low costs and the applicability on formalin-fixed and paraffin-embedded material.

Analysis of proliferative activity in renal lesions induced by N-nitrosobis(2-oxopropyl)amine (BOP) in male Syrian golden hamsters

Binding of a specific antibody to proliferating cell nuclear antigen (PCNA) and staining of argyrophilic proteins associated with nucleolar organizer regions (AgNORs) were investigated in proliferative lesions induced by N-nitrosobis(2-oxopropyl)amine (BOP) in the hamster kidney. Thirty male Syrian golden hamsters were given three weekly s.c. injections of BOP (10 mg/kg body wt.) and sacrificed for characterization of proliferative changes 30 weeks after the first BOP treatment. Morphologically, lesions of the tubular epithelia were classified either as tubular adenoma or dysplasia, the latter being further classified into small cluster, acidophilic cell, clear cell and cystic types. Immunohistochemistry for PCNA revealed significant increases of cell proliferation activity in adenomas and acidophilic cell types of dysplasia, along with significantly elevated mean numbers of AgNORs per nucleus. The results thus indicate that the acidophilic cell type of dysplasia may be of prime significance as the preneoplastic renal lesion induced by BOP.

Promoting effects of ethinyl estradiol on development of renal proliferative lesions induced by N-nitrosobis (2-oxopropyl)amine in female Syrian golden hamsters

The modulating effects of female sex hormones, ethinylestradiol and levonorgestrel, on the development of renal proliferative lesions after initiation with N-nitrosobis(2-oxopropyl)amine (BOP) were investigated. Three groups of female Syrian golden hamsters, each comprising 30 animals, were given four weekly s.c. injections of BOP (10 mg/kg body weight) and then fed diet containing 1 ppm ethinylestradiol (group 1: BOP/EE), diet containing 10 ppm levonorgestrel (group 2) or basal diet (group 3) for the next 27 weeks. As hormone controls, two groups of 20 female hamsters each received diet containing 1 ppm ethynylestradiol (group 4) and 10 ppm levonorgestrel (group 5) from week 3 for 27 weeks without the prior initiation treatment. The severity of diffuse anisokarya, characterized by varied nuclear size and the incidence of dysplasias of the proximal tubular epithelia induced by BOP, were significantly increased in the BOP/EE group, indicating the promoting effects of the hormone. In the renal dysplastic lesions (small-cluster, cystic, clear-cell and acidophilic cell types), adenomas and nephroblastomas, increases in the numbers of argyrophilic proteins associated with nucleolar organizer regions (NOR) in the nucleus, suggesting a high proliferative activity, were seen in dysplasia of acidophilic cell types and adenomas. In addition, the number of bizarre NOR per nucleus was significantly higher in adenomas than in dysplasias and highest in nephroblastomas. This morphological change in NOR should therefore be a useful parameter for the diagnosis of malignancy of renal tumors.

Correlation of two AgNOR counts with Ki-67 labeling index: a study in fine-needle aspirates of lymphoproliferative disorders and breast carcinoma

The Ki-67 antibody binds to nonresting cells where Ki-67 labeling index (KLI) reflects proliferative activity (PA). The argyrophilic nucleolar organizer regions (AgNOR) counts have been correlated to ploidy and/or PA. Two AgNOR counting methods distinguish ploidy from PA. The first count is the mean AgNOR count (mAg-NOR) which correlates with ploidy. The second is the percentage of nuclei with > or = 5 AgNORs/nucleus (pAgNOR) which reflects PA. To explore this relationship, we separately stained smears of 20 fine-needle aspirates (FNAs) of lymphoproliferative disorders (n = 12) and breast carcinomas (n = 8) for AgNOR and Ki-67. We also double-stained 10 of the smears for both AgNOR and Ki-67. The correlation of pAgNOR counts and KLI was statistically significant (P < 0.0001) whereas it was not between mAgNOR and KLI (P = 0.13). Additionally, using the double stain, the Ki-67 negative cells had an AgNOR granule range of 1-3/nucleus with a mean of 1.33 (+1.86 SD). The Ki-67 positive cells showed an AgNOR granule range of 2-12/nucleus with a mean of 4.15 (+/- 1.02 SD) (P < 0.0002). We thus conclude that pAgNOR is a more reliable indicator of PA than mAgNOR and that four AgNORs/nucleus is an acceptable number differentiating proliferating from resting cells.

Proliferative activity in the malignant cellular blue nevus

The proliferative activity of four malignant cellular blue nevi (MCBN) was assessed in routinely fixed, paraffin-embedded material using staining for the argyrophilic nucleolar organizer regions (AgNORs), immunohistochemical staining for proliferating cell nuclear antigen (PCNA [PC10]), and DNA flow cytometry. The objective was to determine whether the evaluation of proliferative activity could represent a useful diagnostic parameter. Four cellular blue nevi (CBN), 10 melanocytic nevi (MN), four common blue nevi (BN), and 10 conventional malignant melanomas (MMs) were selected as controls. In the MCBN the mean AgNOR number, evaluated on the basis of 100 tumor cells, was 8.33 +/- 0.83; NORs were small and dispersed throughout the nucleus; the mean PCNA score was 31.93% +/- 4.4; and two of the cases were aneuploid and two diploid. In the CBN the AgNOR count was 3.69 +/- 0.56; NORs were large and mainly grouped in a central cluster; the mean PCNA score was 3.53% +/- 1.28; and three of the cases were diploid and one aneuploid. The AgNOR counts in the MCBN were significantly different from those in the CBN (P = .0002), MN (3.04; P = .00001), and BN (2.93; P = .00006), whereas they were not significantly different from those in the conventional MMs (7.64; P = .58). The PCNA (PC10) scores in the MCBN were significantly different from those in the CBN (P = .00003), MN (2.05%; P = .00001), and BN (5.06%; P = .00002), whereas they were not significantly different from those in the conventional MMs (28.9%; P = .49). In all the cases a linear relationship between AgNOR counts and PCNA scores was observed (r = .94, P = .00001). Our results indicate that AgNOR analysis and PCNA immunostaining can be regarded as useful additional parameters for the diagnosis of MCBN.

The prognostic significance of AgNOR counts in lymph node deposits of breast carcinomas

Low AgNOR counts in metastatic lymph node deposits confer a longer 5-year survival rate in patients with breast carcinoma compared with those having high AgNOR counts. This was demonstrated in a series of 30 axillary lymph nodes from an equal number of patients with malignant breast disease. The beneficial effect of the low AgNOR status was independent of tumour differentiation, tumour size and the patients' age using univariate analysis, but it was related to the number of lymph nodes with metastatic disease. It is thought that AgNOR counts in axillary lymph node metastases may be an additional prognostic variable in assessing breast tumour behaviour.

Nucleolar organizer regions as markers of incipient cellular alterations in squamous epithelium

Transcriptionally active nucleolar organizer regions identified by silver staining (AgNOR) vary in number with cellular activity and/or malignant transformation and have been used as a diagnostic tool. A morphometric study of AgNORs was performed in an experimental model of irradiated squamous epithelium (Wistar rat sole skin) 4, 8, and 14 hours and 1, 2, 5, and 7 days post-irradiation with 50 Gy of x-rays. A statistically significant and progressive rise in AgNOR average volume of up to 238% and reduction in AgNOR number/nucleus of up to 40% were detected as a function of post-irradiation time. A statistically significant 46% increase in AgNOR volume was detected as early as 8 h post-irradiation, when no histological changes were observable in routine preparations. These results suggest that AgNORs may be useful as a quantitative marker of incipient changes in cellular activity and caution against the indiscriminate use of AgNORs in the follow-up of lesions which may have been exposed to radiotherapy. Furthermore, this study suggests the possibility of using AgNORs as a sensitive biological dosimeter in cases of uncontrolled exposure to radiation.

Comparing flow cytometric analysis and nucleolar organizer region enumeration in archival oral premalignant lesions

Flow cytometric analysis (FCA) and silver colloidal nucleolar organizer region-associated protein staining (AgNOR) have been used individually in assessing the histopathologic nature of various human tumors. However, few researchers have investigated the relationship between the two techniques in a single series. In a retrospective study, we examined 36 premalignant lesions of the oral cavity by FCA and AgNOR on formalin-fixed, paraffin-embedded tissue submitted to the University of Tennessee, Memphis, oral pathology laboratory. Three categories of epithelial dysplasia were represented (9 mild, 9 moderate, 6 severe), as well as four epithelial hyperplasias without dysplasia, three squamous cell carcinomas, and five fibrous nodules as controls. Parameters recorded for each case included age, race, gender, site, light microscopic diagnosis (LMD), DNA index (DI), total proliferative index (TPI), S-phase (S), range of nucleolar organizer regions (RNOR), and mean number of nucleolar organizer regions (MNOR). The average maximum nucleolar organizer region count (AMXNOR) for each LMD category was also calculated. The objective of the study was to determine if FCA or AgNOR aided in the subjective LMD of oral premalignant lesions and if the parameters recorded for the specimens exhibited any positive correlation. The FCA results indicated an abnormal DI in 6 of the 24 dysplastic lesions. A positive partial correlation was seen between DI and MNOR (r = 0.434; P < 0.012) and TPI and S (r = 0.774; P < 0.0001), holding gender and race constant. Additionally, the AMXNOR exhibited a slight tendency to increase for each increasing grade of dysplasia but this could not be confirmed statistically.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleolar organizer regions in determining malignancy of pigmented conjunctival lesions

We assessed the usefulness of silver staining of nucleolar organizer regions in the diagnosis of pigmented conjunctival tumors. Fifty-one biopsy specimens were silver stained to identify the nucleolar organizer regions. Nineteen nevi without atypia, three nevi with atypia, eight primary acquired melanosis lesions, and 14 melanomas were studied. In each specimen, silver staining of the nucleolar organizer regions was counted in 100 cells to yield an average of the silver staining of the nucleolar organizer region count. The mean silver staining of the nucleolar organizer region counts per cell was correlated with the degree of malignancy of pigmented conjunctival lesions as follows: nevi, 3.0; primary acquired melanosis, 3.2; nevi with atypia, 3.9; primary acquired melanosis with atypia, 5.0; and melanoma, 5.7 (Spearman correlation [rS] = .83, P = .0001; analysis of variance [ANOVA] F test = 20.9, P = .0001). A cutoff value of 4.0 (mean silver staining of nucleolar organizer regions per cell) will differentiate melanoma and primary acquired melanosis with atypia from other lesions (sensitivity, 100%; specificity, 96%). The silver staining of nucleolar organizer regions is a useful adjunct in determining the malignancy of pigmented conjunctival tumors.

The nucleolar organizer regions in hyperplastic and tumorous lesions of the human liver

The alterations of the argyrophil nucleolar organizer regions (AgNORs) have been studied in hyperplastic and neoplastic human liver lesions. The material studied included: 11 focal nodular hyperplasias (FNH), 3 adenomas, 19 hepatocellular carcinomas (HCC), 2 hepatoblastomas, 8 liver metastases. In 5 cases tumor-free (normal) liver was also available for study. The mean AgNOR numbers were significantly increased in all of these lesions (in FNHs 3.36 +/- 1.43, in the adenomas 2.48 +/- 1.29, in the HCCs 3.32 +/- 1.43, in the hepatoblastomas 3.33 +/- 1.33 and in the metastases 4.86 +/- 1.54) compared to those observed in normal liver (0.86 +/- 0.85). The highly increased AgNOR number in FNHs was particularly surprising and it seemed to us that based on AgNOR numbers the FNHs could be divided into two groups. With the exception of hepatoblastomas in all primary liver lesions the AgNOR counts distributed on a rather broad scale resulting in overlapping in hyperplastic and tumourous cases. The authors concluded that the AgNOR counts reflect only the proliferative activity of a given cell population and at least in the liver they cannot serve as basis for distinction between the hyperplastic, benign and malignant neoplastic lesions.

Central neurocytoma: proliferative assessment by nucleolar organizer region staining

Proliferative potential of four cases of central neurocytoma were assessed by a silver colloid staining technique for argyrophilic protein associated with nucleolar organizer regions (AgNORs). All but one tumor had an Ag-NOR score of less than 2 and were regarded as a benign entity. However, one tumor tissue from a patient suffering from a recurrent central neurocytoma after 13 years from the first operation possessed a 2.06 AgNOR score, which is not significantly different from others. It is considered that central neurocytoma is an essentially benign neoplasm, even though the tumor is recurrent. The present study revealed the usefulness of AgNOR staining for a retrospective assessment of the proliferative potential of central neurocytomas.

Multiple agminated pigmented Spitz nevi (mimicking acral lentiginous malignant melanoma and dysplastic nevus) in an African-American girl

BACKGROUND

Reed's nevi are distinguished from Sptiz tumors by their significant melanogenesis and growth pattern. They may be confused with melanoma on clinical and histologic grounds.

CASE REPORT

An unusual case in which multiple agminated Reed's nevi mimicked acral lentiginous malignant melanoma in an African-American girl is presented. A critical review of the literature is presented to assist in the diagnosis.

CONCLUSIONS

Awareness of this entity and of its possible clinical presentations and judicious application of conventional hematoxylin-eosin microscopic criteria remain the most useful methods to bring the correct diagnosis in most instances. Mutilating or excessive surgery may be avoided for most cases of pigmented spindle and epithelioid cell nevus.

Morphological changes of the nucleolar organizer regions induced by 7,12-dimethylbenz[a]anthracene in the hamster cheek pouch

The staining of nucleolar organizer regions (NORs), which equate to rDNA transcription, was applied to chemically induced-lesions of the hamster cheek pouch. The cheek pouches of 16 male golden Syrian hamsters were treated three times a week with 0.5% 7,12-dimethylbenz[a]anthracene (DMBA) in mineral oil for 16 weeks. The percentage of gathered-type NORs with high activity nucleoli increased in the pouch epithelium during DMBA treatment and reached the highest values in malignant tumors. The percentage of dispersed-type NORs also increased in the malignant lesions. However, the absolute number of NORs was not affected by DMBA treatment. These results suggest that DMBA induces modification of NOR activity at the early stages of carcinogenesis and shows the potential of this model for studying NOR alterations in neoplasia.

The first normal oral mucosa epithelium in which gamma-glutamyl transpeptidase activity has been detected

A portion of consistently gamma-glutamyl transpeptidase-positive epithelium in the normal oral mucosa of rats is described. This is the first normal oral mucosa epithelium reported to express activity of the transpeptidase. This enzyme has been used as a marker of malignant transformation in tissues such as epidermis and oral mucosa epithelium. Complementary studies of the enzyme-positive portion of oral mucosa and a neighbouring negative portion, suggest that, in this model, expression of gamma-glutamyl transpeptidase is linked to a terminally-differentiated epithelium.