Patient-reported, clinical and radiological factors associated with the result after non-surgical management of acute AC joint dislocation Rockwood type III and V.

PURPOSE: The treatment of Rockwood type III and V acromioclavicular (AC) joint dislocations is controversial, and an individualized treatment algorithm is yet to be developed. The objective of this study was to investigate the association of demographical, clinical, patient-reported and radiological variables with the Western Ontario Shoulder Instability Index (WOSI) score and risk of surgery. METHODS: Inclusion criteria for this prospective cohort study were patients aged 18-60 with an acute AC joint dislocation with >25% increase in the coracoclavicular distance on bilateral Zanca radiographs. Patients were treated non-surgically with 3 months of home-based training and the option of delayed surgical intervention. The outcomes were the WOSI score and surgery yes/no. Demographical, clinical, patient-reported (WOSI and Shoulder Pain and Disability Index [SPADI]) and radiological variables were collected at baseline and 6 weeks after the injury and investigated for association with the outcomes at 3 months, 6 months and 1 year. RESULTS: Ninety-five patients with Rockwood type III/V AC joint dislocation were included. Pre-injury participation in overhead/collision sports was a risk factor for surgery with an odds ratio of 5 (p = 0.03). Reduced range of motion (ROM) at baseline was associated with reduced WOSI scores and increased risk of surgery. At 6 weeks, reduced ROM, increased SPADI and increased pain during cross-over were associated with the outcomes. Radiological measurements were not correlated with the result. At the 6 weeks follow-up, patients eventually requiring surgery could be detected with a sensitivity of 100% and a specificity of 94% based on a SPADI score of >30 and a ROM ≤ 140° in shoulder flexion or abduction. CONCLUSION: ROM was the only variable consistently associated with both WOSI and risk of surgery. Six weeks after the injury, it was possible to detect patients in need of surgery based on ROM and SPADI with a sensitivity of 100% and a specificity of 94%. LEVEL OF EVIDENCE: Level II.

The ISAKOS subclassification of Rockwood type III AC joint dislocations in a stable type A and an unstable type B is not clinically relevant.

PURPOSE: The treatment of Rockwood type III AC joint dislocations has been debated for decades. In 2014, the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS) Upper Extremity Committee suggested a subclassification of the injury into type A, considered stable and best treated nonsurgically, and type B, considered unstable and best treated surgically. Type B is defined by the presence of scapular dyskinesis and overriding of the clavicle to the acromion on a modified lateral radiograph. The objective of the study was to investigate if this subclassification is clinically relevant. METHODS: This was a prospective cohort study. Inclusion criteria were patients aged 18-60 years with acute AC joint dislocation and a baseline Zanca radiograph with an increase in the CC distance of >25% compared to the uninjured side. All patients were treated nonsurgically with 3 months of home-based training and with the option of delayed surgical intervention. Patients were assessed at baseline and at follow-ups 6 weeks, 3 months, 6 months and 1 year after the injury. At the 6-week follow-up, patients were graded as stable and unstable according to the ISAKOS criteria. Outcomes were the Western Ontario Shoulder Instability Index (WOSI) and referral for surgery. RESULTS: At 6 weeks of follow-up, 20 patients were classified as stable type A and 69 were classified as unstable type B. The ISAKOS subclassification was not clinically relevant, but patients graded as stable had statistically significantly better WOSI scores at 6 months compared to the unstable group (p = 0.03) but not at 3 months or 1 year. Nine patients (9.5%), all from the unstable group, were referred for surgery. No patients from the stable group underwent surgery (n.s). CONCLUSION: The ISAKOS subclassification of Rockwood type III in a stable type A and an unstable type B is not clinically applicable. LEVEL OF EVIDENCE: Level II.

A hereditary genetic marker closely associated with microsatellite instability in lung cancer.

Alterations in 5 microsatellite loci were analyzed in tumors from 137 patients with primary non-small cell lung carcinomas that were also genotyped for the Hras1 variable number of tandem repeats (VNTR) locus. Twenty-nine patients (21%) had changes in at least one microsatellite locus. A majority of these cases (24 of 29, 83%) had VNTR alleles classified as rare in the population. The frequency of these rare alleles were significantly higher among lung cancer patients than in healthy controls (P = 0.016 or 1.80; 95% confidence interval = 1.13-2.85). Microsatellite alterations were significantly more frequent among patients with at least one rare Hras1 VNTR allele (24 of 40, 60%) compared to patients with two common alleles (5 of 97, 5%; P < 0.001 or 27.6; 95% confidence interval = 8.18-82.9). Microsatellite alterations were also more frequent among patients below 50 years of age (8 of 21, 38%) than for older patients (21 of 112, 19%).

Different susceptibility to smoking-induced DNA damage among male and female lung cancer patients.

The levels of aromatic/hydrophobic DNA adducts were analyzed in normal lung tissue from 63 lung cancer patients and examined in relation to exposure and genetic factors. Adduct levels were significantly higher in smokers than in nonsmokers, but among smokers the number of cigarettes smoked per day had only low significance for the variation in adduct levels. An inverse correlation was found between years of smoking and DNA adduct levels (r = 0.52, P = 0.001). Thus, patients with high adduct levels generally had shorter duration of smoking and/or lower smoking dose before the clinical onset of the disease, which fits expected behavior of cancer susceptible individuals. The data indicated an excess of individuals with glutathione S-transferase M1 deficiency among male patients with high adduct levels. Among females the DNA adduct levels were higher than in males when adjusted for smoking dose. There was a highly significant difference in the distribution of males and females when smokers were divided into quartile groups according to adducts per pack year (trend test: 2-sided P = 0.005). This may indicate that women are at greater risk of tobacco-induced lung cancer.

Sex differences in lung CYP1A1 expression and DNA adduct levels among lung cancer patients.

Several epidemiological studies have indicated that female tobacco smokers may be at higher risk of lung cancer than males. In a study of lung cancer cases, we have found that female smokers had a significantly higher level of aromatic/hydrophobic DNA adducts in their nontumor lung tissue (15.39+/-9.47 adducts/10(8) nucleotides, n = 29) than male smokers (12.08+/-8.14, a = 93; P = 0.047). Females had significantly higher levels of adducts/pack-year (females 0.95+/-0.82 adducts/pack-year and males 0.46+/-0.46; P = 0.0004) and adducts/cigaret/day (females 1.48+/-1.29 and males 0.89+/-0.74, P = 0.015). By quantitative reverse transcription-PCR, it was found that female smokers exhibited a significantly higher expression level of lung CYP1A1 (494+/-334 CYP1A1 mRNA/10(6) glyceraldehyde-3-phophate dehydrogenase mRNA, n = 15) compared with males (210+/-208, n = 12; P = 0.016). Furthermore, for both sexes combined a significant correlation between CYP1A1 expression and DNA adduct level was found (r = 0.50, P = 0.009). In conclusion, the observed sex difference in aromatic/hydrophobic DNA adduct levels may at least in part be explained by different levels of CYP1A1 expression.

p53 mutations in lung tumors: relationship to putative susceptibility markers for cancer.

We have screened 108 non-small cell lung tumors for mutational alterations in the p53 gene (exons 5 through 8) using polymerase chain reaction and denaturing gel electrophoresis techniques. Thirty-four cases (32%) had aberrant band migrations. The following DNA-sequencing step confirmed the mutations in all these samples. Seventy-six % of the mutations were found at G:C base pairs. Of all the mutations found, 29% were GC to AT, 29% GC to TA, 15% AT to GC, 12% GC to CG, and 3% AT to CG. The other mutations (12%) were deletions or insertions of one base pair. The frequency of p53 mutations among heavy smokers was higher than in nonsmokers (P = 0.047; odds ratio, 6.75; 95% confidence interval, 0.80-57). We examined p53 mutations in relation to genotypes of GSTmu1 and H-ras1. Our data showed that nearly all heavy smokers with transversion mutations were homozygous for the GSTmu1 null allele (10 of 11). The frequency of such mutations was significantly higher for patients with two null alleles (10 of 25) than for those with at least one allele intact (1 of 18) (P = 0.011; odds ratio, 11.33; 95% confidence interval, 1.29-99.3). This study indicated that rare alleles at the variable number of tandem repeats region flanking the H-ras protooncogene are negatively associated to the presence of p53 mutations in the tumors (P = 0.009).

Altered p53 gene structure and expression in human epithelial cells after exposure to nickel.

The carcinogenicity of certain nickel compounds is well known. We have previously shown that human kidney epithelial cells were immortalized by treatment with Ni(II) and in cooperation with the v-Ha-ras oncogene transformed the cells to acquire tumorigenicity in athymic nude mice. Immunocytochemistry and sequence analysis of DNA from the nickel-immortalized cells revealed abnormal p53 expression and a T----C transition mutation in codon 238. These data are consistent with the hypothesis that Ni(II)-induced mutation in the p53 gene can be involved in the escape from senescence of kidney epithelial cells.

Microsatellite instability is associated with tumors that characterize the hereditary non-polyposis colorectal carcinoma syndrome.

Microsatellite instability implying multiple replication errors (RER+ phenotype) characterizes a proportion of colorectal carcinomas, particularly those from patients with the hereditary non-polyposis colorectal carcinoma syndrome. We studied the incidence of microsatellite instability in more than 500 sporadic tumors representing 6 different types of cancer. Apart from colorectal carcinoma [see the paper by Lothe et al. (Cancer Res., 53:5849-5852, 1993)] the RER+ phenotype was found in 18% (6 of 33) of gastric carcinomas and 22% (4 of 18) of endometrial carcinomas. In contrast, no evidence of this abnormality was detected in cancers of the lung (N = 85), breast (N = 84), and testis (N = 86). Importantly, the first three cancers, as opposed to the latter three, are characteristic of the hereditary non-polyposis colorectal carcinoma syndrome. These findings suggest that the cancers belonging to the hereditary non-polyposis colorectal carcinoma tumor spectrum may have essential pathogenetic steps in common, including a tendency to multiple replication errors.

Mutability of p53 hotspot codons to benzo(a)pyrene diol epoxide (BPDE) and the frequency of p53 mutations in nontumorous human lung.

p53 mutations are common in lung cancer. In smoking-associated lung cancer,the occurrence of G:C to T:A transversions at hotspot codons, e.g., 157, 248, 249,and 273, has been linked to the presence of carcinogenic chemicalsin tobacco smoke including polycyclic aromatic hydrocarbons suchas benzo(a)pyrene (BP). In the present study, we have used a highly sensitive mutation assay to determine the p53 mutation load in nontumorous human lung and to study the mutability of p53 codons 157, 248, 249, and 250 to benzo(a)pyrene-diol-epoxide (BPDE), an active metabolite of BP in human bronchial epithelial BEAS-2B cells. We determined the p53 mutational load at codons 157, 248, 249, and 250 in nontumorous peripheral lung tissue either from lung cancer cases among smokers or noncancer controls among smokers and nonsmokers. A 5-25-fold higher frequency of GTC(val) to TTC(phe) transversions at codon 157 was found in nontumorous samples (57%) from cancer cases (n = 14) when compared with noncancer controls (n = 8; P < 0.01). Fifty percent (7/14) of the nontumorous samples from lung cancer cases showed a high frequency of codon 249 AGG(arg) to AGT(ser) mutations (P < 0.02). Four of these seven samples with AGT(ser) mutations also showed a high frequency of codon 249 AGG(arg) to ATG(met) mutations, whereas only one sample showed a codon 250 CCC to ACC transversion. Tumor tissue from these lung cancer cases (38%) contained p53 mutations but were different from the above mutations found in the nontumorous pair. Noncancer control samples from smokers or nonsmokers did not contain any detectable mutations at codons 248, 249, or 250. BEAS-2B bronchial epithelial cells exposed to doses of 0.125, 0.5, and 1.0 microM BPDE, showed G:C to T:A transversions at codon 157 at a frequency of 3.5 x 10(-7), 4.4 x 10(-7), and 8.9 x 10(-7), respectively. No mutations at codon 157 were found in the DMSO-treated controls. These doses of BPDE induced higher frequencies, ranging from 4-12-fold, of G:C to T:A transversions at codon 248, G:C to T:A transversions and G:C to A:T transitions at codon 249, and C:G to T:A transitions at codon 250 when compared with the DMSO-treated controls. These data are consistent with the hypothesis that chemical carcinogens such as BP in cigarette smoke cause G:C to T:A transversions at p53 codons 157, 248, and 249 and that nontumorous lung tissues from smokers with lung cancer carry a high p53 mutational load at these codons.

p53 mutations in defined structural and functional domains are related to poor clinical outcome in non-small cell lung cancer patients.

The prognostic value of p53 status in non-small cell lung cancer has been investigated in 148 patients with clinical stage I-IIIB disease. Tumor tissues were examined for mutations in exons 4-9, with emphasis on defined structural and functional domains. Eighty-four mutations were detected in 83 (54%) of the patients. Eighty-eight percent of the mutations were within exons 5-8, and 12% of the mutations were within exons 4 and 9. Missense mutations occurred in 67% of the tumors, and 30% were null mutations (10% stop mutations, 15% frameshift mutations, and 5% splice site mutations). Patients with mutations in p53 had a significantly higher risk for lung cancer-related death and for death from all causes than those with wild-type p53 [hazard ratio (HR) = 2.09 and 95% confidence interval (CI) = 1.20-3.64 and HR = 1.69 and 95% CI = 1.06-2.70, respectively]. Mutations in p53 related to even still poorer lung cancer-related prognosis were found at the following locations: (a) exon 8 (HR = 3.5; 95% CI, 1.59-7.71)]; (b) the structural domains L2 + L3 (HR = 2.36; 95% CI, 1.18-4.74), and (c) codons involved in zinc binding (HR = 11.7; 95% CI, 3.56-38.69). Together, the biologically functional group of severe flexible mutants (codons 172, 173, 175, 176, 179, 181, 238, 245, and 267) and severe contact mutants (248, 282) were significantly related to shorter lung cancer-related survival (HR = 4.16; 95% CI, 1.93-8.97). Squamous cell carcinoma was the dominant histological type in tumors involved in poor prognosis in exon 8 (HR = 3.19; 95% CI, 1.07-9.45). These results indicate that mutations in defined structural and functional domains of p53 may be useful molecular biological markers for prognosis and treatment strategy in non-small cell lung cancer patients.

Human CYP1A1 (cytochrome P(1)450) gene: lack of association between the Msp I restriction fragment length polymorphism and incidence of lung cancer in a Norwegian population.

In this study of 221 lung cancer patients and 212 controls, no association between a Msp I polymorphism in the CYP1A1 gene and an increased risk of lung cancer was found. Histological type, smoking habits and family history were also examined. No associations between the Msp I restriction fragment length polymorphism in the CYP1A1 gene and any of these parameters were found. These results are in contrast to a previous report by a Japanese group (Kawajiri et al., 1990) who found an association between the less common allele and an increased susceptibility to lung cancer in their population. The frequency of the less common Msp I 1.9 kb fragment allele (C2) appears to be three times greater in the Japanese population than in the Norwegian population and a Caucasian population of North America. It is possible that in the Asian population this Msp I polymorphism is in linkage disequilibrium with another mutation important for CYP1A1 gene expression, whereas in the Caucasian population these mutations are in equilibrium.

Inhibitory action of hexavalent chromium (Cr(VI)) on the mitochondrial respiration and a possible coupling to the reduction of Cr(VI).

The reduction of hexavalent chromium (Cr(VI] in isolated liver mitochondria was studied under different redox conditions in the respiratory chain. With 25 microM Na2CrO4 the rates were 1.6 +/- 0.7, 13.9 +/- 0.6 and 12.7 +/- 0.7 nmole Cr(VI) reduced 15 min/mg protein with the electron transport chain oxidized, reduced and only complex 1 reduced respectively. Electrons from succinate, bypassing complex 1, were apparently unavailable for Cr(VI)-reduction. The kinetics of chromate reduction was studied with only complex 1 in a reduced state. A rapid and a slow phase were found, probably corresponding to different electron donors in the mitochondria. Blocking the free thiols with N-ethylmaleimide lead to less than 10% decrease in the rapid initial Cr(VI)-reduction and to about 20% decrease during the whole incubation period (15 min). The amounts of free thiols were moderately decreased (15%) in chromate treated mitochondria during the slow reduction of Cr(VI) only. SH-groups may thus participate as reductants during the slow reduction phase. The respiration rate was inhibited about 50% by 25 microM Na2CrO4 when the mitochondria oxidized NAD-linked substrates. In contrast, succinate stimulated respiration was inhibited 50% by 3.6 mM Na2CrO4. The observed inhibition was Na2CrO4 in the micromolar range was therefore probably localized at complex 1 and may be coupled to the reduction of Cr(VI) at the same place. The respiration of isolated hepatocytes was also affected by Na2CrO4. Five micromolar chromate caused 5-10% inhibition. The inhibitory action of chromate on the mitochondrial respiration may thus constitute an important cytotoxic mechanism.

Nickel-induced alterations in human renal epithelial cells.

Cellular progression to malignancy appears to require a number of distinct steps in which genetic damage in key regulatory genes accumulates. Immortalization, or escape from senescence, is considered to be one of the first phenotypic changes. Ni2+ treatment of normal human kidney epithelial (NHKE) cells in vitro resulted in immortalization of the cells IHKE cells). The combined action of Ni2+ and v-Ha-ras oncogene fully transformed the cells to tumorigenicity in athymic nude mice. Sequence analysis of DNA from IHKE cells revealed point mutation in the p53 gene at codon 238 with T-->C transition. These findings suggest that Ni-induced mutation in the p53 gene can be involved in the immortalization of the NHKE cells. The results also show that changes in the responses to EGF and TGF beta and in the expression of their receptors occur during malignant progression in vitro.

Allele diversity of the H-ras-1 variable number of tandem repeats in Norwegian lung cancer patients.

We have examined restriction fragment length polymorphisms of the H-ras-1 gene in germ-line DNA from 214 lung cancer patients and 309 unaffected controls. When DNA samples were digested with MspI/HpaII, Southern blot analysis revealed at least 22 different alleles, grouped according to their frequencies as common, intermediate, and rare. The frequency of rare alleles in lung cancer patients (16/428) is significantly different (p = 0.002) from that in the control group (5/618). Individuals with rare alleles were found to be at 4.7-fold greater risk of lung cancer than those with no rare alleles.

DNA mismatch binding in human lung tumor cell lines.

Defects in mismatch repair (MMR) genes have been involved in several types of sporadic and hereditary cancers. In order to elucidate the role of MMR in human lung carcinogenesis we examined DNA mismatch binding in cell-free extracts of seven lung tumor cell lines and five corresponding lymphoblastoid cell lines from lung cancer patients. Using the technique of bandshift assay we have demonstrated that 2/7 of the tumor cell lines are aberrant in binding to specific DNA mismatches while all lymphoblastoid cell lines were proficient in binding to all tested mismatches. Both extracts were aberrant in binding to G/T mismatch whereas one of the cell lines showed deficiency in binding to the C:A mismatches as well. Immunoblotting analysis showed that all known DNA mismatch repair (MMR) proteins were present in these extracts. The cell line deficient in binding to both G:T and C:A mismatches showed microsatellite instability (MSI) in tumor DNA and higher resistance to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). This report indicates that DNA mismatch binding deficiencies may be implicated in at least a subgroup of human lung cancer.

Hras1 VNTR alleles as susceptibility markers for lung cancer: relationship to microsatellite instability in tumors.

PURPOSE: To further evaluate lung cancer risk associated with rare Hras1 VNTR alleles and possible biological mechanisms. MATERIALS AND METHODS: The Hras1 VNTR was genotyped in 295 lung cancer patients and 500 healthy controls by PCR and high resolution electrophoresis. Microsatellite alterations were examined in 168 tumors by PCR and capillary electrophoresis. RESULTS: 35 Hras1 VNTR alleles were found, of which 24 were defined as rare. A relative risk of 3.3 (95% CI; 1.9-6.0) associated with rare alleles was obtained using the total groups. Increased risk was significant both for males and females. When a matched control group was used, a relative risk of 12.7 (95% CI; 1.7-93.9) was calculated for individuals with rare alleles at the Hras1 VNTR locus. A low frequency of microsatellite alterations was observed (4.7%) in lung tumors. The frequency of altered microsatellite loci was higher among patients with rare Hras1 VNTR alleles than among patients with common alleles. CONCLUSION: Rare Hras1 VNTR alleles are associated with lung cancer risk, and a genetic mechanism which increases allelic diversity may be involved.

Mechanisms of chromium toxicity in mitochondria.

The oxygen consumption of isolated rat heart mitochondria was potently depressed in presence of 10-50 microM Na2CrO4 when NAD-linked substrates were oxidized. The succinate stimulated respiration and the oxidation of exogeneous NADH in sonicated mitochondria were not affected by chromate at this concentration range. A rapid and persistent drop (40% in 2 min) in the mitochondrial NADH level was observed after chromate addition (30 microM) under conditions which generally should promote regeneration of NADH. Experiments with bis-(2-ethyl-2-hydroxybutyrato)oxochromate(V) and vanadyl induced reduction of Cr(VI) in presence of excess NADH were performed. These experiments indicated that NADH may be directly oxidized by Cr(V) at physiological pH. The activity of 10 different enzymes were measured after lysis of intact mitochondria pretreated with chromate (1-100 microM). Na2CrO4 at a very low level (3-5 microM) was sufficient for 50% inhibition of alpha-ketoglutarate dehydrogenase. Higher concentrations (20-70 microM) was necessary for similar effect on beta-hydroxybutyrate and pyruvate dehydrogenase. The other enzymes tested were unaffected. Thus, the chromate toxicity in mitochondria may be due to NADH depletion as a result of direct oxidation by Cr(V) as well as reduced formation of NADH due to specific enzyme inhibition.

Microsomal metabolism of hexavalent chromium. Inhibitory effect of oxygen and involvement of cytochrome P-450.

The reduction of hexavalent chromium (Cr(VI] by rat liver microsomes was studied. With 15-120 microM Na2CrO4 microsomes (0.5 mg protein/ml) effectively reduced Cr(VI) in the presence of NADPH provided anaerobic conditions. Phenobarbital (PB) and Aroclor 1254 (PCB) pretreatment increased microsomal Cr(VI) reduction while CoCl2 reduced the rate. The rates with 30 microM Na2CrO4 were: 6.4 +/- 0.1, 7.8 +/- 0.7, 13.4 +/- 0.5, 2.95 +/- 0.09 nmol Cr.mg prot.-1 min-1 for control, PB, PCB and cobalt pretreated microsomes respectively. Kinetic studies gave a Michaeli-Menten like first-order kinetics with increases both in Km and Vmax values after pretreatment with PB or PCB. CO partly inhibited the microsomal Cr(VI) reduction. The CO-sensitive reduction rate was directly correlated to the cyt. P-450 content of the different microsomal preparations. Substituting NADH for NADPH gave approximately 27% lower activity with 30 microM Na2CrO4. This activity was neither inducible by cyt. P-450 inducers nor influenced by CO. Oxygen 1.0% and 0.10% gave approximately 100% and 30% inhibition of Cr(VI) reduction (30 microM Na2CrO4) respectively, and an uncompetitive like inhibitory pattern was found. No redox cycling of Cr(VI) was seen. 51Cr binding to the microsomes was approximately 10% after complete reduction of 30 microM Na2CrO4. Externally added FMN, Fe3+-ADP and nitrobenzen stimulated microsomal Cr(VI) reduction. A 60% higher reduction rate of Cr(VI) by isolated hepatocytes was found during anaerobic in comparison with aerobic conditions.

Gene-environment interactions in human lung cancer.

Gene-environment interactions are thought to be critical for several diseases such as cancer, diabetes, heart disease and asthma. Cancer is a result of multiple gene-environment interactions occurring over several decades. During tumor development the cell accumulates multiple genetic changes, which generate the transformed phenotype, i.e. a cell with increased genetic instability. Lung cancer is a useful model for the study of the interplay between genetic factors and environmental exposure since the primary etiology is well established. Several polymorphic enzymes that may be important determinants of susceptibility have been demonstrated. Data also provide evidence for sex differences in lung cancer susceptibility. Furthermore, certain chemical carcinogens may contribute to the carcinogenic process in the lung epithelial cells by inducing genomic instability either directly or indirectly through inflammatory processes.

Nickel(II) induces microsatellite mutations in human lung cancer cell lines.

Nickel(II) is a human carcinogen causing respiratory cancers. The purpose of this study was to determine whether Ni(II) may induce microsatellite mutations in human cells. We transfected the three human lung tumor cell lines A427, HCC15 and NCI-H2009 with a mammalian expression vector containing a (CA)(13) repeat in the coding sequences of the reporter hygromycin gene (hyg). A total of 33 clones carrying the integrated vector derived from the three cell lines was investigated for spontaneous and Ni(II)-induced hygromycin-resistant (hyg(r)) reversion mutants. Significantly higher frequencies of hyg(r) reversion mutations were observed in Ni(II)-treated cells (NCI-H2009 and HCC-15) than control cells. In the majority of the colonies hyg(r) phenotype was due to mutations within the integrated (CA) repeat sequence. The type of mutations consisted of both contraction and expansion of the (CA) repeat unit. The finding that Ni(II) promotes microsatellite mutations raises the possibility that genetic instability may be a mechanism involved in nickel carcinogenesis.