Patterns of wave break during ventricular fibrillation in isolated swine right ventricle

Several different patterns of wave break have been described by mapping of the tissue surface during fibrillation. However, it is not clear whether these surface patterns are caused by multiple distinct mechanisms or by a single mechanism. To determine the mechanism by which wave breaks are generated during ventricular fibrillation, we conducted optical mapping studies and single cell transmembrane potential recording in six isolated swine right ventricles (RV). Among 763 episodes of wave break (0.75 times x s(-1) x cm(-2)), optical maps showed three patterns: 80% due to a wave front encountering the refractory wave back of another wave, 11.5% due to wave fronts passing perpendicular to each other, and 8.5% due to a new (target) wave arising just beyond the refractory tail of a previous wave. Computer simulations of scroll waves in three-dimensional tissue showed that these surface patterns could be attributed to two fundamental mechanisms: head-tail interactions and filament break. We conclude that during sustained ventricular fibrillation in swine RV, surface patterns of wave break are produced by two fundamental mechanisms: head-tail interaction between waves and filament break.

Tp53 gene therapy: a key to modulating resistance to anticancer therapies?

Abnormalities in the p53 tumor suppressor have been identified in over 60% of human cancers. The status of p53 within tumor cells has been proposed to be one of the major determinants of the response to anticancer therapies. In this review we examine the relationship between functional p53 and sensitivity, or resistance, to chemotherapy and radiotherapy. We also discuss the potential of current gene-therapy approaches to restore functional p53 to tumors as a means of modulating the effects of radiation and chemotherapy.

Does p53 status influence tumor response to anticancer therapies?

Abnormalities in the tumor suppressor gene p53 have been identified in over 60% of human cancers. Since it plays such a pivotal role in cell growth regulation and apoptosis, the status of the p53 gene has been proposed as one of the major determinants of a tumor's response to anticancer therapies. In this review we examine the relationship between functional p53 and sensitivity/resistance to both chemotherapy and radiotherapy, and discuss the potential use of some of the current gene therapy approaches to restore functional p53 to tumors as a means of modulating the effects of radiation and chemotherapy.

Are medical students comfortable with practicing physical examinations on each other?

PURPOSE

To assess medical student attitudes toward, and comfort with, taking turns practicing peer physical examinations (PPEs) on fellow classmates.

METHOD

A questionnaire with 25 Likert-scaled questions was administered to 164 end-first-year medical students at the University of Minnesota, Minneapolis. Topics assessed included: (1) comfort with various aspects of PPEs; (2) attitudes regarding the professionalism, appropriateness, and perceived value of PPEs; (3) attitudes toward peer breast, genital, and rectal exams; and (4) the effects of age and gender on response.

RESULTS

Of the 164 students surveyed, 124 (76%) responded. Almost all (98%) agreed that PPEs are appropriate, valuable, and a comfortable experience. Fewer students were comfortable with performing inguinal examinations and conducting PPEs with students of the opposite gender. Twelve percent of the students expressed difficulty in setting limits with peers, and 48% felt exposed when undressed as an examination model in front of a group of peers. The majority of students were opposed to peer breast, genital, and rectal examinations. Some statistically significant gender differences and age/gender interactions were observed.

CONCLUSION

Results suggest that this sample of medical students was very comfortable with PPEs and willing to participate in PPEs, although a few students were uncomfortable with these examinations. No extensive curricular change appears warranted, though steps can be taken to maximize overall student comfort and to accommodate the few students who do not favor PPEs.

Non-viral gene delivery for p53

Abnormality in the tumor suppressor gene p53 is one of the most common occurrences associated with human neoplasia. Consequently, restoration of wild-type p53 function is seen as a particularly promising approach for cancer gene therapy. In recent years, considerable research effort has centered upon developing and improving non-viral delivery systems as alternatives to viral vectors for gene delivery. These methods include the use of lipoplexes and polyplexes, and even delivery of naked DNA. Optimally effective cancer gene therapy requires treatment of metastatic as well as local disease, and to achieve this end, systemic delivery systems for therapeutic genes will be required. This review will discuss some of the recent advances in ways to improve targeting, transfection efficiency and stability for systemic, non-viral p53 gene therapy.

Inhibition of Ras p21 synthesis by antisense undecamers with uniform and specifically arranged phosphorothioate linkages

The design of chimeric oligodeoxynucleotides (ODNs) in which certain phosphodiester linkages are replaced by phosphorothioate (PS) aims to decrease non-sequence-specific effects of uniform PS ODNs and to preserve the PS-provided protection against exo- and endonucleases. This study has, for the fist time, directly compared the differences in nuclease resistance, cellular uptake, antisense potency and sequence specificity of PS and end-capped, pyrimidine-protected (PPS) undecamer ODNs, that are complementary to the initiation codon region of human Ha-ras mRNA. At concentrations above 5 microM, both PS and PPS undecamers were moderately and equally stable for over 48 h in complete medium with RS485 cells overexpressing Ha-ras. They were completely stable at 0.4 microM when complexed with Lipofectin reagent that enhanced cellular uptake up to 9-fold. Both the antisense PPS and PS undecamers produced well-defined inhibition of Ras p21 synthesis in both cell-free and cell-based assays. However, non-sequence-specific effects of the uniform phosphorothioates were still significant. In contrast, the antisense PPS undecamer, when delivered to RS485 cells with Lipofectin reagent, inhibits human Ras p21 synthesis by more than 90% at a concentration of 3.2 microM, while the effect of controls with inverted, mismatched or scrambled sequence was minimal (5% or less) on p21 synthesis and RS485 cell growth.

3'-End conjugates of minimally phosphorothioate-protected oligonucleotides with 1-O-hexadecylglycerol: synthesis and anti-ras activity in radiation-resistant cells

Activation of the ras oncogene has been implicated in many types of human tumors. It has been shown that downmodulation of ras expression can lead to the reversion of the transformed phenotype of these tumor cells. Antisense oligodeoxyribonucleotides (ODNs) can inhibit gene expression by hybridization to complementary mRNA sequences. To minimize toxicity associated with all-phosphorothioated ODNs and improve cellular uptake, we used partially phosphorothioate (PPS)-modified ODNs having an additional hydrophobic tail at the 3'-end (PPS-C(16)). The PPS ODNs are protected against degradation by PS internucleotide linkages at both the 3'- and 5'-ends and additionally stabilized at internal pyrimidine sites, which are the major sites of endonuclease cleavage. Here we show that anti-ras PPS-C(16) ODN retains the high sequence-specificity of PPS ODNs and provides maximal inhibition of Ras p21 synthesis with minimal toxicity even without the use of a cellular uptake enhancer. Moreover, treatment of T24, a radiation-resistant human tumor cell line that carries a mutant ras gene, with anti-ras PPS-C(16) ODN resulted in a reduction in the radiation resistance of the cells in vitro. We also demonstrate that the growth of RS504 (a human c-Ha-ras transformed NIH/3T3 cell line) mouse tumors was significantly inhibited by the combination of intratumoral injection of anti-ras PPS-C(16) ODN and radiation treatment. These findings indicate the potential of this combination of antisense and conventional radiation therapy as a highly effective cancer treatment modality.

Transferrin-liposome-mediated systemic p53 gene therapy in combination with radiation results in regression of human head and neck cancer xenografts

The use of cationic liposomes as nonviral vehicles for the delivery of therapeutic molecules is becoming increasingly prevalent in the field of gene therapy. We have previously demonstrated that the use of the transferrin ligand (Tf) to target a cationic liposome delivery system resulted in a significant increase in the transfection efficiency of the complex [Xu, L., Pirollo, K.F., and Chang, E.H. (1997). Hum. Gene Ther. 8, 467-475]. Delivery of wild-type (wt) p53 to a radiation-resistant squamous cell carcinoma of the head and neck (SCCHN) cell line via this ligand-targeted, liposome complex was also able to revert the radiation resistant phenotype of these cells in vitro. Here we optimized the Tf/liposome/DNA ratio of the complex (LipT) for maximum tumor cell targeting, even in the presence of serum. The efficient reestablishment of wtp53 function in these SCCHN tumor cells in vitro, via the LipT complex, restored the apoptotic pathway, resulting in a significant increase in radiation-induced apoptosis that was directly proportional to the level of exogenous wtp53 in the tumor cells. More significantly, intravenous administration of LipT-p53 markedly sensitized established SCCHN nude mouse xenograft tumors to radiotherapy. The combination of systemic LipT-p53 gene therapy and radiation resulted in complete tumor regression and inhibition of their recurrence even 6 months after the end of all treatment. These results indicate that this tumor-specific, ligand-liposome delivery system for p53 gene therapy, when used in concert with conventional radiotherapy, can provide a new and more effective means of cancer treatment.

[The effect of thermal power plant on microbial ecology and environmental quality]

To investigate the effect of thermal power plant on the microbial ecology and the environmental quality, the Hsieh-Ho Thermal Power Plant was chosen and the populations of microbes including bacteria, actinomycetes, fungi, and cellulolytic, phosphate-solubilizing and nitrogen-fixing microbes were selected as the parameters of microbial ecology. The pH values of the soil sample collected from inside and outside of the plant were 5.2-6.2 and 4.0-5.3, respectively. Moisture content in plant area was lower than that in the surrounding area. Microbial populations of the topsoils were higher than those of the subsoils. Each gram of soil contained 3.64 x 10(4)-5.16 x 10(7) colonies of bacteria, 1.75 x 10(3)-1.10 x 10(6) colonies of actinomycetes and 6.72 x 10(3)-8.78 x 10(6) colonies of fungi in the plant area; while they were 5.52 x 10(4)-2.14 x 10(7), 8.26 x 10(3)-7.25 x 10(5) and 3.49 x 10(3)-2.74 x 10(6) colonies of bacteria, actinomycetes and fungi, respectively, in the surrounding area. The effect of seasonal change on microbial populations was not significant. The ratio of cellulolytic, phosphate-solubilizing and nitrogen-fixing microbes to the total count in the plant area was also higher than that in the surrounding area, and some of them had significant differences. From the statistical analysis, the effect of thermal power generator on the population and distribution of microbes was significantly different.

Restoration of the G1 checkpoint and the apoptotic pathway mediated by wild-type p53 sensitizes squamous cell carcinoma of the head and neck to radiotherapy

BACKGROUND

A significant number of squamous cell carcinomas of the head and neck (SCCHN) resist radiation treatment, the most common form of adjuvant therapy for this disease. The presence of a mutant form of the tumor suppressor gene p53 has been correlated with disruption of programmed cell death (apoptosis) and reduced cell cycle arrest, resulting in increased radiation resistance and survival.

METHODS AND RESULTS

We introduced by means of an adenoviral vector a functional p53 gene into a radiation-resistant SCCHN cell line that harbors mutant p53. Replacement of wild-type p53 restored the G1 block and apoptosis in these cells in vitro. Moreover, introduction of wild-type p53 sensitized SCCHN-induced mouse xenografts to radiotherapy in vivo.

CONCLUSION

The combination of p53 replacement gene therapy with conventional radiotherapy may treat SCCHN more effectively.

p53 mediated sensitization of squamous cell carcinoma of the head and neck to radiotherapy

Radiation resistant squamous cell carcinoma of the head and neck cell line JSQ-3 carries a mutant form of tumor suppressor gene p53. Treatment of these cells with an adenoviral vector containing wild-type p53 (Av1p53) was able to inhibit their growth in vitro and in vivo while having no effect on normal cells. More significantly, introduction of wtp53 also reduced the radiation-resistance level of this cell line in vitro, in a viral dose-dependent manner. Furthermore, this radiosensitization also carried over to the in vivo situation where the response of JSQ-3 cell-induced mouse xenografts to radiotherapy was markedly enhanced after treatment with Av1p53. Complete, long-term regression of the tumors for up to 162 days was observed when a single dose of Av1p53 was administered in combination with ionizing radiation, demonstrating the effectiveness of this combination of gene therapy and conventional radiotherapy. This sensitization of tumors to radiation therapy by replacement of wtp53 could significantly decrease the rate of recurrence after radiation treatment. Since radiation is one of the most prevalent forms of adjunctive therapy for a variety of cancers, these results have great relevance in moving toward an improved cancer therapy.

Transferrin-liposome-mediated p53 sensitization of squamous cell carcinoma of the head and neck to radiation in vitro

Wild-type (wt) p53 DNA was transfected into the radioresistant human cell line JSQ-3, established from a squamous cell carcinoma of the head and neck (SCCHN), using a transferrin-liposome system, and the ability of the introduced wt p53 to sensitize the transfected JSQ-3 cells to ionizing radiation was examined. Transferrin increased the in vitro transfection efficiency of cationic liposomes up to 70-80% in JSQ-3 cells, representing a 6- to 10-fold increase over liposome transfection alone. The exogenous wt p53 was expressed at high levels in transferrin-liposome-DNA-transfected cells and resulted in the reversion of the radioresistant phenotype of the JSQ-3 cells in a DNA dose-dependent manner. The D10 values were reduced from 6.36 +/- 0.54 Gy to 4.13 +/- 0.06 Gy, a value in the radiosensitive range. In vivo, the intratumoral injection of the transferrin-liposome system resulted in a higher number of transfected tumor cells in the JSQ-3 induced nude mouse xenografts when compared with transfection by liposome alone. The results indicate that the combination of p53 replacement gene transduction, mediated by the relatively safe transferrin-liposome system, and conventional ionizing radiation may provide a more effective treatment for head and neck cancer.

Evidence supporting a signal transduction pathway leading to the radiation-resistant phenotype in human tumor cells

A signal transduction pathway, involving oncogenes and their normal counterparts the proto-oncogenes, analogous to that for cell growth and differentiation has been proposed to lead to the phenotype of cellular radioresistance (RR). In this report we provide evidence demonstrating the existence of such a pathway by using antisense oligonucleotides (ASO) to reverse the RR phenotype. Utilizing ASO directed against the raf-1 gene, a central component of this proposed pathway, we were able to reverse the RR phenotype of human tumor cell lines having elevated HER-2 expression or a mutant form of Ha-ras, two genes upstream of raf-1 in signal transduction. Additionally, anti-ras ASO were able to radiosensitize HER-2 overexpressing cells. These results, which verify the presence of a signaling pathway leading to cellular RR, also have possible clinical implications for the use of ASO as a means to sensitize radioresistant tumors to radiation therapy.

Harmonic analysis of homogeneous networks

We introduce a generalization of mutually inhibitory networks called homogeneous networks. Such networks have symmetric connection strength matrices that are circulant (one-dimensional case) or block circulant with circulant blocks (two-dimensional case). Fourier harmonics provide universal eigenvectors, and we apply them to several homogeneous examples: k-wta, k-cluster, on/center off/surround, and the assignment problem. We also analyze one nonhomogeneous case: the subset-sum problem. We present the results of 10000 trials on a 50-node k-cluster problem and 100 trials on a 25-node subset-sum problem.

Cytogenetic response to G2-phase X irradiation in relation to DNA repair and radiosensitivity in a cancer-prone family with Li-Fraumeni syndrome

Noncancerous skin fibroblasts from six family members with Li-Fraumeni syndrome, five with cancer of diverse tissue origin and one with a premalignant neoplasm, showed a high frequency of chromatid aberrations, 94 to 119 breaks and 58 to 95 gaps per 100 metaphase cells arrested with colcemid 0.5 to 1.5 h after X irradiation (1.75 x 10(-2) C/kg). This response results from deficient repair of the radiation-induced DNA damage. In contrast, skin fibroblasts from two unrelated normal controls and a spouse showed 19 breaks and 17 to 19 gaps per 100 cells. Whereas all six members of the cancer-prone family had a radioresistant phenotype, only four had an inherited p53 mutation. Fibroblasts from a radioresistant family member showed the same extent of chromatid damage directly (0 to 0.5 h) after G2-phase X irradiation as those from the radiosensitive control spouse. We conclude, therefore, that radiosensitivity, as determined by cell killing in asynchronous populations of skin fibroblasts, is unrelated to chromosomal sensitivity to G2-phase X irradiation. However, the persistence of a high frequency of chromatid breaks and gaps at 0.5 to 1.5 h after G2-phase X irradiation, a manifestation of deficient DNA repair, is associated with proneness to cancer in this family.

Expression of the c-erbB-2 (HER-2/neu) oncoprotein in human prostatic carcinoma

The objective of this study was to determine the expression of the c-erB-2 oncoprotein via immunohistochemistry of archival clinically localized human prostate cancers and to compare these results to known clinical prognostic factors. In addition, positive staining cases were subjected to differential polymerase chain reaction to assess for c-erbB-2 gene amplification. Immunohistochemical staining with a polyclonal antibody (pAb 1) was performed on archival radical prostatectomy specimens. To standardize the staining, positive and negative control material was generated using c-erbB-2 transfected NIH3T3 cells grown on agar plugs, formalin fixed, paraffin embedded and processed on glass slides for immunohistochemistry. Definite positive membranous staining was detected in 18 of 53 neoplastic cases (34%). In addition, 9 cases of benign prostatic hyperplasia were stained without evidence of c-erbB-2 expression detected. Either focal or diffuse membranous staining was identified in 6 of 27 (22%) well, 8 of 20 (40%) moderately and 4 of 6 (66%) poorly differentiated tumors (p = 0.03, chi-square test for trend). Positive staining occurred in 6 of 18 patients (33%) with pathological stage B and 12 of 33 (36%) with pathological stage C disease. At a mean of 36 months, complete followup was available for 16 of the 18 positive cases and 30 of the 35 negative cases. For stage B 1 of 6 positive (16.7%) versus 1 of 12 negative (8%) staining cases showed progression (p = 1.0). For stage C 7 of 12 positive (58.3%) versus 9 of 21 negative (42.9%) cases showed progression (p = 0.48). Deoxyribonucleic acid was extracted from the exact same archival paraffin blocks for the c-erbB-2 protein positive cases and subjected to differential polymerase chain reaction analysis, which revealed no c-erbB-2 gene amplification. This study demonstrates that approximately a third of all clinically localized prostate cancers express the c-erbB-2 oncoprotein via immunohistochemistry using pAb-1 on archival material, c-erbB-2 oncoprotein expression does not appear to be a prognostic marker for prostate cancer although our results are preliminary and, although oncoprotein expression was detected, no positive case demonstrated deoxyribonucleic acid amplification.

Dominant negative effect of a germ-line mutant p53: a step fostering tumorigenesis

Lysates derived from the fibroblasts of individuals who are homozygous for normal p53 or heterozygous for the germ-line p53 mutation characteristic of certain Li-Fraumeni cancer-prone families were assessed for p53 function utilizing the binding of p53 protein to a p53-specific consensus oligonucleotide sequence. As expected, control nuclear lysates containing only mutant p53 or no p53 displayed little or no such binding. However, the nuclear lysates from heterozygous fibroblasts containing similar amounts of normal p53 and 245D mutant p53 displayed binding that was significantly below 50% of that seen with homozygous wild-type p53 in normal cell lysates. The nuclear lysates of these heterozygous or homozygous fibroblasts exhibited similar levels of DNA binding to a consensus oligonucleotide specific for the transcription factor, AP-1. These results indicate that mutant p53 has a transdominant effect on the binding of DNA by normal p53. These findings also suggest that p53 complexes formed in vivo that contain mutant p53 are functionally impaired even if normal p53 is also present in the complex. The implications of a trans-dominant effect of mutant p53 on the cancer-prone phenotype of individuals heterozygous for mutated p53 in Li-Fraumeni families is discussed.

Several mutant p53 proteins detected in cancer-prone families with Li-Fraumeni syndrome exhibit transdominant effects on the biochemical properties of the wild-type p53

The identification of germ-line mutations in the p53 gene has provided a situation where comparable amounts of wild-type and mutant p53 co-exist in constitutional cells of certain individuals who are cancer-prone. Here we report the biochemical characteristics of several Li-Fraumeni syndrome associated mutant p53 proteins in order to assess the influence of germ-line mutant p53 on the functions of the wild-type p53. Unlike 248W mutant p53 protein, which was previously shown to have no effect on the wild-type p53 conformation (Milner & Medcalf, 1991; Cell 65, 765-774), germ-line associated mutant p53 proteins with residue 133T, 245D or 258K, converted the wild-type p53 conformation into the mutant conformation. Furthermore, lysates containing cotranslated wild-type p53 and these mutant p53 proteins were significantly impaired for DNA and SV40 large T antigen binding. These observations suggest that at least some germ-line p53 mutants might exhibit dominant effects on wild-type p53 functions and, like other mutant p53 proteins, the phenotype of germ-line mt p53 proteins might be variable depending on the particular mutation.

Oncogene- transformed NIH 3T3 cells display radiation resistance levels indicative of a signal transduction pathway leading to the radiation-resistant phenotype

Oncogenes and their normal counterparts, proto-oncogenes, are functionally important cellular genes which interact with one another as components of signal transduction pathways leading to cell growth and differentiation. Numerous reports in the literature have also begun to link these genes to the phenomenon of cellular radiation resistance. In this report we examine the radiation resistance level of NIH 3T3 cells transformed by various oncogenes in an attempt to define the intracellular pathway to the radiation-resistant phenotype. The results demonstrate that an analogous signaling pathway is apparently involved in acquisition of radiation resistance. Serine/threonine protein kinase oncogenes such as raf, mos, and PKC play a central role in the pathway. Moreover, specific oncogenes upstream (sis, HER-2, met, trk, and ras) and downstream (ets and myc) of these important signaling mediators can also influence the radiation resistance level of the cells.

Absent ras gene mutations in human adrenal cortical neoplasms and pheochromocytomas

A variety of human tumors have been studied for ras mutations to date. However, little is known about the prevalence and significance of ras gene activation in adrenal neoplasms. Recently, a study of 10 primary human pheochromocytomas found no evidence for ras mutations. To our knowledge no survey of ras mutations in adrenocortical neoplasms has been reported. Therefore, we analyzed deoxyribonucleic acid (DNA) from 17 archival tumors (8 adrenocortical carcinomas, 6 pheochromocytomas, 2 adrenal adenomas, 1 aldosteronoma, 2 fresh pheochromocytomas and 1 fresh benign adrenal gland) for activating mutations at the 12, 13 and 61 codons of N-ras, H-ras and K-ras. DNA was extracted from archival tissues using 3 different methods: a simplified boiling method, a proteinase-K-phenol chloroform extraction and a novel heat-stable protease Thermus rt41A technique. The boiling and heat-stable protease methods provided for more consistent polymerase chain reaction amplifications than the more laborious phenol chloroform method. This heat-stable protease Thermus rt41A method had not been reported previously for use in archival DNA extraction. Polymerase chain reaction amplified the ras gene regions of interest, and mutations were screened by mutation-specific oligonucleotide probe hybridization of Southern and slot blots. Polymerase chain reaction-generated mutation-specific positive and negative controls were used in the hybridization protocol. With these controlled conditions no definite mutations were detected at codons 12, 13 or 61 of N, H or K-ras. Ras activation via point mutations at these codons rarely, if ever, occurs in adrenal neoplasms.

Altered messenger RNA and unique mutational profiles of p53 and Rb in human esophageal carcinomas

Seventy-nine esophageal carcinoma patients were studied for genetic abnormalities in the p53 and Rb tumor suppressor genes. Single-strand conformation polymorphism analysis and DNA sequencing were used to detect p53 point mutations, Northern blotting was used to examine abnormal expression of p53 and Rb, and polymerase chain reaction and Southern blotting were used to analyze allelic loss. Twenty-five cases were analyzed by DNA sequencing to detect mutations in p53. Fourteen samples contained mutations within exons 5 through 9 of p53; seven had missense mutations giving rise to single amino acid substitutions. The remaining seven (50%) contained nonsense mutations leading to premature termination, five due to single base pair substitutions, and two that were the result of frameshift mutations. In other human tumors, p53 mutations are predominantly missense mutations, but our data as well as those from other groups show that nonsense mutations are common in human esophageal cancer. All but one of the constitutionally heterozygous samples containing mutations also manifested loss of the normal p53 allele; the one exception without allelic loss contained a silent mutation, which should not have had any affect on the p53 protein product. In addition, Northern blotting analysis revealed abnormalities (altered transcript size or mRNA levels) in 5 of 7 cases involving p53 and in 2 of 7 cases analyzed for Rb. Thirty-four cases were informative for allelic loss studies of both p53 and Rb; of these, 25 (74%) lost heterozygosity of p53, Rb, or both. When point mutations and mRNA expression abnormalities were also considered, 33 of 45 (73%) tumors informative for allelic loss assays of both genes as well as for mRNA or point mutation studies showed one or more abnormalities in p53 or Rb. Our results strongly suggest that a unique profile of molecular alterations involving p53 and Rb characterizes human esophageal cancer and that these specific genetic lesions are important in the development and/or progression of most human esophageal carcinomas.

Detection of RAS mutations in archival testicular germ cell tumors by polymerase chain reaction and oligonucleotide hybridization

Preliminary studies of RAS mutational activation in human testicular germ cell neoplasms have yielded conflicting results. Whereas two studies of clinical material revealed a significant incidence of N- and KRAS mutations, two studies of a variety of germ cell lines failed to document RAS mutations. To clarify the incidence of RAS mutations in these tumors, we studied archival paraffin-embedded, formalin-fixed orchiectomy specimens from 25 nonseminomas (NSGCT), 18 seminomas (SEM), and one Leydig cell tumor. For 14 of the 44 neoplasms, DNA was also available from nonmalignant testis adjacent to the tumor. Six age-matched patients had testes removed because of nonmalignant disease and were studied as controls. Polymerase chain reaction (PCR) amplified the K-, N-, and HRAS 12, 13, and 61 codons of these specimens, and mutations were detected with mutation-specific oligonucleotide probe hybridization of Southern and slot blots. Four mutations were found in KRAS 12 (4/44;[9.1%]). One seminoma [1/18(5.6%)] contained the mutation GGT(GLY)----CGT(ARG), and three NSGCT [3/25(12%)] were found to have GGT(GLY)----GAT(ASP) mutations. One of the NSGCT mutations was detected in adjacent nonmalignant tissue, but the corresponding tumor did not contain any detectable mutation. No mutations were detected at KRAS 13 or 61, in NRAS or HRAS 12, 13, or 61, or in the control normal testes. PCR, slot blots, and hybridizations were performed twice by two separate investigators for confirmation of results. PCR-generated mutation-specific positive controls were created for all possible RAS mutations, and these along with wild-type DNA controls were integral to interpretation of the oligonucleotide mismatch hybridization assay. By using positive and negative controls, we have detected a relatively low incidence of RAS mutations in archival human testicular germ cell tumors.