Immunohistochemical Detection Of P53 Protein Research Articles

Immunohistochemical detection of p53 protein in basal cell skin cancer after microwave-assisted antigen retrieval

p53 is the most frequently altered tumor-suppressor gene in skin cancer. In normal tissues the p53 protein (wild type) has a very short half-life and it is not detectable immunohistochemically. In contrast, the mutant p53 protein has an extended half-life in tumor cells and can be detected by immunohistochemical methods. p53 is widely used as an indicator of tumor aggression and progression. Fixation methods especially formaldehyde based fixation may mask the immunohistochemical detection of p53 protein but antigen retrieval methods enhance the inmmunohistochemical detection of p53 protein by remodification of protein structure. This study was designed to evaluate the efficacy of different fixatives, of microwaving and microwave pretreatment method to retrieve p53 immunoreactivity in paraffin-embedded non-lesioned (adjacent normal tissue) human skin samples or pathological human skin samples diagnosed as basal cell carcinoma. The samples were fixed at RT and/or in microwave oven either in neutral buffered formalin or alcohol for different time periods. For antigen retrieval, the sections were irradiated in a microwave oven for 5 cycles in 10 mM citrate buffer (pH 6.00). In this study the effects of six different fixation methods on the immunohistochemical staining have been investigated in basal cell tumor specimens. The application of antigen retrieval method was also examined and compared. Optimal results were obtained using samples fixed in alcohol either at room temperature (24 h) or in microwave oven.

Gallbladder carcinoma: the role of p53 protein overexpression and Ki‐67 antigen expression as prognostic markers

The overexpression of p53 protein and the expression of Ki-67 antigen may affect the survival of patients with gallbladder carcinoma. This association has been tested in a series of 41 patients with relatively early carcinoma of the gallbladder. Forty-one surgical specimens from patients with a postoperative histological diagnosis of gallbladder carcinoma were studied. All patients were operated by simple cholecystectomy only because the tumours were not advanced and/or their general condition was poor. Patients submitted to radical operations were excluded. p53 expression was calculated from nuclear staining according to the intensity and extent of positive cells, as graded on a scale from 1 to 3; a combined score of >3 was considered as overexpression. Ki-67 expression was calculated by the MIB-I index: the percentage of positively stained tumour cell nuclei out of the total tumour cells counted (n = 1000); >20% of stained cells was considered positive. Twenty-nine gallbladder carcinomas (71%) overexpressed p53 protein in the cell nuclei. No significant differences were found in relation to cell differentiation on the level of tumour infiltration through the gallbladder wall. Five-year survival of patients with gallbladder carcinoma overexpressing p53 was 17.2%, while survival of patients without p53 overexpression was 30% (not significant). Twenty-four cases (58.5%) were considered positive for the MIB-I index. There were no differences between the grade of cell differentiation and wall infiltration. Five-year survival of the patients with a MIB-I positive index was 9.2% as opposed to 27.7% for those with a negative index (not significant). p53 protein nuclear overexpression and Ki-67 protein expression in gallbladder carcinoma were not related to histological differentiation, level of gallbladder wall invasion or patient survival.

Immunohistochemical expression of p53, fibroblast growth factor-b, and transforming growth factor-alpha in feline vaccine-associated sarcomas.

Fifty feline sarcomas associated with vaccine-site injection were evaluated to determine the immunohistochemical expression of p53 protein, basic fibroblast growth factor (FGF-b), and transforming growth factor-alpha (TGF-alpha). Forty-one tumors (82%) were fibrosarcomas (FS), eight (16%) were malignant fibrous histiocytomas (MFH), and one (2%) was a chondrosarcoma (CS). Overexpression of p53 protein was observed in the nuclei of tumor cells in 28 (56%) sarcomas; FGF-b expression was found in the cytoplasm of tumor cells in 40 (80%) feline sarcomas, but the staining was more intense in the spindle-shaped cells of FS than in polygonal or round cells of MFH. The single CS faintly expressed FGF-b. The majority of feline vaccine-associated sarcomas (43 of 50, 86%) expressed moderate or intense staining for TGF-alpha in the cytoplasm of tumor cells. Heterogeneous immunolabeling for p53, FGF-b, and TGF-alpha was present in neoplastic, multinucleated giant cells. Intense expression of FGF-b was statistically associated with younger cats (P < 0.01) and with tumors with nodular growth patterns (P = 0.02). In addition, sarcomas negative for p53 protein expressed FGF-b more frequently than did p53-positive tumors (P = 0.04). The frequency of FGF-b immunostaining was significantly higher in sarcomas with intense expression of TGF-alpha (P = 0.05). Immunohistochemical detection of p53 protein, FGF-b, and TGF-alpha suggests that these growth-regulating proteins may play different roles in the development of sarcomas associated with vaccine sites.

P53 gene mutations are associated with poor survival in low and low-intermediate risk diffuse large B-cell lymphomas

Backgroundp53 alterations have been associated with a poor prognosis in aggressive B-cell lymphoma. We investigated the clinical relevance of p53 status in diffuse large B-cell lymphoma (DLBCL), focusing on patients who belong to lower risk groups of the international prognostic index and were uniformly treated. We aimed to determine whether this biological marker could identify among such patients those with a pejorative outcome who could benefit from a distinct therapeutic approach. Patients and methodsWe studied 69 patients presenting with no, one (low-risk, n = 40) or two (low-intermediate risk, n = 29) risk factors treated with an anthracyclin-containing induction regimen. p53 exons 5–8 mutations were screened for using denaturing gradient gel electrophoresis and confirmed by direct sequencing. Immunohistochemical detection of p53 protein and of its downstreamtarget p21 were also evaluated in 60 of 69 cases. Resultsp53 mutations were detected in 16 of 69 (23%) lymphoma samples. The presence of a p53 gene mutation affected survival (P = 0.01), with a 6-year survival rate estimated to be 44% in mutated patients, compared with 79% in non-mutated ones. Using a stepwise Cox model, p53 mutation constituted the only parameter affecting survival (relative risk = 2.7, P = 0.03). A p53+/p21– immunohistochemical pattern (n = 15), suggestive of a disrupted p53 function, strongly correlated with p53 gene status and was associated with a lower 6-year survival rate when compared with a p53– or p53+/p21+ phenotype (47% versus 74%, P = 0.05). Conclusionsp53 alterations constitute a pejorative biological indicator able to discriminate among clinically defined lower risk patients with DLBCL.

Immunohistochemical detection of tumor suppressor gene p53 protein in feline injection site-associated sarcomas.

Sarcomas associated with injection sites are a rare but important problem in cats. Immunohistochemical detection of p53 protein may correlate to mutation of the p53 tumor suppressor gene, a gene known to be important in oncogenesis. The expression of nuclear p53 protein in 40 feline injection site-assocated sarcomas was examined by immunohistochemical staining. In 42.5% (17/40), tumor cell nuclei were stained darkly; in 20% (8/40), tumor cell nuclei were stained palely; and in 37.5% (15/40), tumor cell nuclei were unstained. Immunohistochemical detection of p53 protein in a proportion of injection site-associated sarcomas suggests that mutation of the p53 gene may play a role in the pathogenesis of these tumors.

Präkanzeröse Läsionen des Endometriums: Aspekte der molekularen Pathogenese und Probleme der Nomenklatur

Für das Endometriumkarzinom (EC), das häufigste Malignom des weiblichen Genitale, lassen sich bisher zwei unterschiedliche Pathogenesewege definieren, denen auch eine biologisch prognostische Bedeutung zukommt. Als Prototyp des sog. Typ- I-Karzinoms gilt das endometrioide Adenokarzinom als häufigster Vertreter des EC mit vergleichsweise deutlich besserer Prognose. Pathogenetisch zeigt das endometrioide Karzinom häufig eine Mikrosatelliteninstabilität sowie K-ras-Mutationen, die bereits auch in vorausgehenden Hyperplasien nachweisbar sind. Mikrosatelliteninstabile Tumoren weisen oft auch Mutationen des PTEN-Gens auf. Alterationen des p53-Gens werden nur bei 10 - 20 % beobachtet, präferenziell bei schlecht differenzierten (G3) Karzinomen. Endometrioide Karzinome sind östrogenabhängig und oft mit endometrialen Hyperplasien assoziiert. Die Nomenklatur dieser Hyperplasien ist derzeit im Fluss. Diskutiert wird eine Zweiteilung in Hyperplasien (glandulär-zystische Hyperplasie und komplexe Hyperplasie) und endometrioide Neoplasie (atypische Hyperplasie und gut differenziertes [G1] Karzinom) und das Konzept der endometrialen intraepithelialen Neoplasie (EIN). Derzeit sollten jedoch noch die Ergebnisse weiterer Studien abgewartet werden, bevor die WHO-Klassifikation der endometrialen Hyperplasien modifiziert wird, deren Änderung auf der Basis eines breiten internationalen Konsens erfolgen sollte. Beim Typ II des EC, dessen Prototyp das serös-papilläre Adenokarzinom ist, lassen sich in mehr als 90 % Mutationen des p53-Tumorsuppressorgens nachweisen, mit einer immunhistochemisch detektierbaren Akkumulation des (aberranten) p53-Onkoproteins intranukleär. Eine Mikrosatelliteninstabilität und K-ras-Mutationen sind seltene Ereignisse. Diese Karzinome mit sehr schlechter Prognose entstehen nicht selten in einem atrophen Endometrium, möglicherweise über eine flache Läsion, die als endometriales intraepitheliales Karzinom bezeichnet wird. Das klarzellige Adenokarzinom steht pathogenetisch dem serös-papillären Typ-II-Karzinom nahe, mit jedoch nachweisbaren Unterschieden.

Roles of p53 and MDM2 in tumor proliferation and determination of the prognosis of transitional cell carcinoma of the renal pelvis and ureter.

The significance of p53 overexpression for the prognosis of transitional cell carcinoma (TCC) of the renal pelvis and ureter remains controversial. Simultaneous evaluation of p53 and MDM2 may enable better prediction of tumor proliferation and patient prognosis than that obtained with evaluation of p53 alone. Immunohistochemical detection of p53 protein, MDM2 protein and Ki-67 antigen as proliferation markers was performed for tissue samples obtained from 74 patients with TCC of the renal pelvis and ureter. The correlations of p53/MDM2 overexpression with conventional pathological features, Ki-67 labelling index (LI) and patient survival were studied. Overexpression of p53 was related to progression of each of the pathological features examined (grade, stage, type of infiltration, vascular invasion and lymphatic invasion) and Ki-67 LI was significantly higher with high p53 expression than with low p53 expression. However, overexpression of MDM2 was related to neither disease progression nor Ki-67 LI. Survival analyses were performed for 66 patients. Univariate analysis showed p53 to be a useful prognostic indicator, but in a multivariate analysis only type of infiltration and Ki-67 LI were independent survival markers, while p53 was not. Overexpression of MDM2 was unrelated to patient survival, and the combination of p53 and MDM2 for survival indication was found not to be useful. Overexpression of p53 is related to disease progression, increased tumor proliferation and patient survival for TCC of the renal pelvis and ureter, but the independent prognostic value of p53 did not reach statistical significance. Combined analysis of MDM2 with p53 cannot be recommended for examination of the malignant potential of TCC of the renal pelvis and ureter.

Prognostic Values of Stromal Proportion and PCNA, Ki-67, and p53 Proteins in Patients with Resected Adenocarcinoma of the Lung

Data from 64 patients who underwent surgical resection of lung adenocarcinomas were studied to identify clinicopathologic markers that might provide prognostic information on the clinical behavior of this neoplasia. Patient staging was performed in accordance with the tumor-node-metastasis system as follows: Stage I (n = 29), Stage II (n = 11), Stage IIIA (n = 21), and Stage IIIB (n = 3). Overall follow-up time corresponded to the follow-up time for patients who were alive and to the survival time for patients who had died, all of them expressed in months. Data included age, staging, histologic type, morphometric assessment of histologic features related to tumor (stroma and vascularization), and immunohistochemical detection of proliferation cell markers (Ki-67 protein and proliferating cell nuclear antigen) and p53 protein. The morphometric assessment was made by the point-counting procedure. Data analysis included Life Tables for Survival and Cox Regression models. Overall follow-up analysis showed that significant univariate predictors (P <.05) were T stage; N stage; tumor stromal proportion; and immunohistochemical indexes of proliferating cell nuclear antigen, Ki-67, and p53 proteins. Variables that presented independent predictive value for overall follow-up with the multivariate model (P <.05) were sex, T stage, N stage, tumor stromal proportion, and immunohistochemical detection of p53 protein. We conclude that tumor stromal proportion and immunohistochemical detection of p53 protein, controlled for sex, T stage, and N stage, may be of critical value in the evaluation of recurrence of lung adenocarcinoma, serving as indicators for a more accurate prognosis.

Immunohistochemical detection of p53 protein could improve the management of some patients with Barrett esophagus and mild histologic alterations.

To determine the usefulness of p53 immunostaining in identifying the subgroup of patients with Barrett esophagus who may be at increased risk of developing adenocarcinoma of the esophagus. Tissue samples of 41 patients with Barrett esophagus and available sequential histologic data were processed for p53 immunostaining. Results from each patient were compared over time, and the results of a subset of patients were compared with each other. We observed a significant correlation between the percentage of samples with p53 expression and the severity of dysplasia. Moreover, in a subset of patients with mild dysplasia (cases classified as showing indefinite dysplasia), we observed a statistically significant difference in the percentage of p53-positive samples between the group that progressed to more severe dysplasia and the group that did not progress. Our results suggest that this procedure, which is technically simple, economical, and quick, could play a role in the evaluation and follow-up of patients with Barrett esophagus.

Immunohistochemical detection of p53 protein in ameloblastoma types

Overexpression of p53 protein in unicystic ameloblastoma (uAB) is denser than in the conventional ameloblastoma (cAB) type, indicating increased wild type p53--suppressing the growth potential of uAB and denoting the early event of neoplastic transformation, probably of a previous odontogenic cyst. Overexpression of p53 in borderline cAB and malignant ameloblastoma (mAB) types might reflect a mutational p53 protein playing an oncogenic role, promoting tumour growth. Overexpression of p53 protein could be a valid screening method for predicting underlying malignant genetic changes in AB types, through increased frequency of immunoreactive cells or increased staining density.

Clinical significance of immunohistochemical detection of p53 protein in pleural effusion and bronchial specimen.

To explore the usefulness of p53 immunohistochemical staining as a marker of malignancy in the diagnosis of lung cancer. The expression of p53 in 57 samples of pleural effusion and 69 bronchial biopsy specimens was investigated by immunohistochemical method. p53 was well preserved in the samples of pleural effusion. p53 positive rate was 0%(0/27) ,33.3 %(2/6) and 54.2%(13/24) respectively in cytologically benign , suspicious but not conclusively malignant and malignant pleural effusion. Benign pleural effusion referred as tuberculous and other inflammatory effusion. p53 poisitive rate was 0%(0/23) ,14.3 %(1/7) and 35.9 % (14/39) in histologically benign , atypical proliferating and malignant bronchial biopsy sample. The cases with p53 immunoreactivity were proved to have lung cancer after follow-up in cytologically suspicious but not conclusively malignant pleural effusion and histologically atypical proliferating bronchial biopsy sample. p53 immunostaining could be useful as a marker of malignancy in the cytologic examination of pleural effusion and bronchial biopsy sample. The presence of p53 immunoreactivity in these samples is strongly suggestive of malignancy , though its absence does not exclude neoplasms.

Immunohistochemical detection of p53 protein in neoplastic, preneoplastic and normal bronchial mucosa specimens obtained during diagnostic bronchoscopy.

The expression of p53 protein was evaluated immunochemically in cancer tissue, preneoplastic lesions and normal bronchial mucosa obtained during diagnostic bronchoscopy from 53 patients with lung cancer and 12 patients with benign lung diseases. In lung cancer patients, positive p53 staining was detected in 26/53 (49%) of the tumour specimens. In preneoplastic lesions p53 positive staining was found in 8 of 24 (33.3%) squamous metaplasia, 1 of 4 hyperplasia and 1 of 3 dysplasia lesions. In the same group of patients, 12 cases were found with positive p53 cells in normal bronchial mucosa. In patients with benign diseases, positive p53 staining was found in 1 of 4 cases with squamous metaplasia and in one normal mucosa. Our results provide evidence that somatic genetic alterations may occur in early stages of lung tumorigenesis, raising the possibility that molecular analyses is useful in the early diagnosis of precancerous lesions of the bronchial mucosa, and results indicate that p53 expression can be studied in small tissue specimens obtained during bronchoscopy.

P53, vessel count, and vascular endothelial growth factor expression in human colon cancer.

We previously demonstrated an association between vascular endothelial growth factor (VEGF), vessel counts and metastasis in human colon cancer specimens. Mutant p53 has been implicated in the regulation of angiogenesis. Immuno-histochemical detection of p53 protein has been associated with p53 gene mutations. We sought to determine a correlation between p53 protein detection (i.e., mutant p53), VEGF expression and vessel counts in human colon cancer. Surgical specimens from 93 patients with colon cancer were stained immuno-histochemically for p53, VEGF and factor VIII. Vessel counts were greater in metastatic tumors than in nonmetastatic tumors and adenomas, and greater in nonmetastatic tumors than in adenomas. Vessel counts were highest in tumors with the highest VEGF expression. Vessel counts and VEGF expression were greater in p53-positive tumors than in p53-negative tumors. p53 expression correlated with both VEGF expression and vessel count. The association of p53 expression with VEGF and vessel count suggests that the poor prognosis associated with p53 mutations may be due, in part, to the role of mutant p53 in promoting angiogenesis.

Prognostic factors in papillary and follicular thyroid carcinomas: p53 expression is a significant indicator of prognosis.

To identify clinical and histologic prognostic factors and to investigate whether immunohistochemical detection of p53 expression might contain prognostic information, a retrospective study of patient and tumor characteristics was performed in 225 cases of papillary and follicular thyroid carcinomas. The analyses were based on cause-specific and crude survival. In univariate analysis, age at diagnosis, tumor size, presence of distant metastases, histology (papillary contra follicular type), extrathyroidal invasion, necrosis in primary tumor, and p53 expression were significant prognostic indicators. For 211 patients (96%) all information was available and Cox's proportional hazard model was applied. The authors found that age, distant metastases, necrosis in primary tumor, extrathyroidal invasion, and p53 expression were significant prognostic factors. Analyses of cause-specific and crude survival gave similar results. The authors conclude that age at diagnosis, presence of distant metastases, necrosis in primary tumor, and extrathyroidal invasion are important prognostic factors, and that immunohistochemical detection of p53 protein in the primary tumor is a significant and independent prognostic indicator, which might be of value in the treatment planning in patients with papillary or follicular thyroid carcinomas.

Immunohistochemical visualization of wild-type p53 protein in paraffin-embedded rat liver using tyramide amplification: zonal hepatic distribution of p53 protein after N-hydroxy-2-acetylaminofluorene administration.

P53 protein plays an important role in regulation of the cell cycle. Recently, a role in tumour genesis has also been suggested. The protein is induced after various forms of DNA damage. Immunohistochemical detection of p53 protein showed positive cells in human skin after UV-irradiation, in mouse skin after benzo[a]pyrene treatment and in mouse spleen, thymus and bone after gamma-irradiation. However, no staining was found in mouse and rat liver with traditional immunohistochemical staining methods due to the low amount of p53 present. This seriously hampered studies on the role of p53 in hepatocarcinogenesis. We have developed a more sensitive immunohistochemical method for staining of p53 in paraffin-embedded sections of rat liver using microwave irradiation for antigen retrieval, avidin-biotin complexing and tyramide amplification. A strong, specific fluorescence signal for p53 was found in hepatocytes of rats that had received the hepatocarcinogen N-hydroxy-2-acetylaminofluorene; in control liver no such p53 staining was observed. The fluorescence was located in the nucleus of hepatocytes in zone 1 of the liver. This agrees with the fact that N-hydroxy-2-acetylaminofluorene causes cytotoxicity in this zone.

Immunohistochemical detection of p53 protein in transitional cell carcinoma of the bladder in correlation to DNA ploidy and pathohistological stage and grade.

Mutations of p53 gene have been found in a variety of human malignancies; however, the impact of immunohistological detection of p53 expression in the development and progression of TCC of the bladder is still uncertain. In the present study, we investigated the p53 oncoprotein expression and compared the findings to DNA ploidy and pathohistological stage and grade. The study included 147 patients with transitional cell carcinoma of the bladder investigated between February 1981 and September 1994. The average age of the 55 women and 92 men was 67 years (range: 20-71 years). A total of 76 patients (52%) had stage pTa to pT1, 35 (24%) stage pT2, 25 (17%) stage pT3, and 11 (7%) stage pT4 disease. Frozen sections of tumor biopsies obtained by transurethral resection were immunohistochemically stained using the monoclonal antibody clone D0-7 (DAKO), which recognized two different epitopes for mutant and wild-type p53 protein. Tumors expressing p53 in more than 10% of the tumor nuclei were regarded as positive. The DNA ploidy was determined by image analysis. Immunohistochemical detection of p53 expression was found in 84 (57%) of the 147 tumors examined. Positive p53 staining was seen in grade I tumors in 10 to 25%, in grade II tumors 25 to 75%, and in grade III up to 58% of the tumor nuclei. There was a positive correlation between p53 expression and pathological stage (28% in pTa, 73% in pT1-2, and 68% in pT3-4 tumors). There was no appreciable relationship between DNA Ploidy and p53. Although carcinomas with p53 expression had a slight tendency to be more prevalent among higher disease stages and poorly differentiated transitional cell carcinoma, immunohistochemical detection of p53 is not a valuable tool for predicting the outcome of patients with TCC or for identifying subgroups of patients that may be at a higher risk for tumor progression.

Detection of numeric abnormalities of chromosome 17 and p53 deletions by fluorescence in situ hybridization in pleomorphic adenomas and carcinomas in pleomorphic adenoma. Correlation with p53 expression.

A fluorescence in situ hybridization (FISH) technique using specific DNA probes allows for the detection of chromosomal aberrations and gene deletions and gains, even in interphase nuclei in human solid tumors. A high frequency of aberrations of chromosome 17 and mutation of the p53 gene have been reported in some human tumors. The correlation of p53 expression with abnormalities of chromosome 17 and p53 gene deletion in salivary gland tumors has not yet been investigated. The authors analyzed the numeric aberrations of chromosome 17 and p53 gene deletions in 11 paraffin embedded pleomorphic adenomas (PA) and 9 carcinomas in pleomorphic adenoma (CIPA), using FISH techniques. The centromere specific DNA probe for chromosome 17 and p53 cosmid DNA probe was used. The aberrations of chromosome 17 and p53 deletion were correlated with immunohistochemical detection of p53 protein. Monosomy 17 was detected in 30.8% of CIPA cells and 29.6% of PA cells, and polysomy 17 was detected in 19.6% of CIPA cells and 9.6% of PA cells. p53 protein expression was observed in 6 of 9 CIPA specimens (66.7%) and 2 of 75 PA specimens (2.7%). Deletion of the p53 gene was frequent in p53 protein positive specimens. A statistically significant correlation existed between p53 protein expression and polysomy 17 (P = 0.0417). It was observed that loss of chromosome 17 may occur in PA before its transformation to carcinoma. p53 expression was frequently associated with deletion of the p53 gene as detected by FISH. Polysomy 17 was more frequent in CIPA than PA and was associated with mutation of p53.

Immunohistochemical Detection of p53 Protein in Rhabdomyosarcoma

Immunohistochemical Detection of p53 Protein in Rhabdomyosarcoma

Immunohistochemical detection of p53 protein in rhabdomyosarcoma: association with clinicopathological features and outcome.

Alteration in the p53 tumor suppressor gene is the most common tumor specific genetic change identified in most major cancer types including rhabdomyosarcomas. To investigate the overexpression of p53 and its relation to clinical features and outcome in patients with rhabdomyosarcoma (RMS), an immunocytochemical study was performed. Formalin-fixed paraffin embedded tissue sections obtained from 42 cases of RMS were immunostained with a mouse monoclonal antibody p53-D07. Staining was assessed by evaluating the percentage of p53 immunopositive cancer cell nuclei. Nuclear accumulation of p53 protein was detected in 8 of 42 (19%) samples. Clinical analyses of patients demonstrated no correlation between positive staining and age, sex, histological subtype, stage and overall survival. This analysis, however, was limited by the small number of patients who demonstrated p53 immunostaining. Nonetheless, a statistically significant association was observed between p53 expression and adverse outcome. Nuclear p53 expression was associated with disease progression or recurrence (p <0.001) and with a worse event free survival (p = 0.0015). The nuclear p53 immunoreaction rate is low in RMS, but p53 expression appears to correlate with poor prognosis.

Immunohistochemical Study of p53 Protein Expression in Spitz Nevus as Compared with Other Melanocytic Lesions

The accumulation of p53 protein was studied immunohistochemically on paraffin-embedded sections of 26 Spitz nevi (SNs), 26 primary invasive cutaneous malignant melanomas (MMs), 20 metastases of MM, and 17 ordinary compound nevi (CNs), using monoclonal antibody BP53-12. Positive reactivity was detected in some of the tumor cells in seven (35%) metastatic MMs, all exhibiting strong nuclear staining; eight (31%) primary MMs, of which seven showed strong nuclear staining; two (7%) SNs, of which only one showed strong nuclear staining; and none of the CNs. The frequencies of the positively stained lesions in general, and the strongly positively stained lesions in particular, in the MM and metastatic MM groups were each statistically significantly higher than the respective frequencies in the SN and CN groups. We believe that the immunohistochemical detection of p53 protein with the use of monoclonal antibodies such as BP53-12 on paraffin sections, especially when strong nuclear reactivity is demonstrated, may prove to be an adjunctive tool in the histopathologic differentiation of MM from SN.