Accumulation of genetic alterations in brain metastases of sporadic breast carcinomas is associated with reduced survival after metastasis.

Tumor progression is characterized by stepwise accumulation of genetic alterations. To identify alterations associated with breast cancer metastasis, an analysis of comparative loss of heterozygosity (LOH) was performed on 38 primary sporadic breast carcinomas and 16 distant metastases. Two loci at 5q21 and 18q21 were chosen because of their reported increased deletion frequency in metastatic tumors. LOH at 17q21, 13q12-13, 17p13.1 and 11q22-23 was analyzed to determine whether there is a specific involvement of these breast cancer-associated gene loci in the metastatic process. Our data show that distant metastases are characterized by markedly increased LOH frequency at all loci examined. In both gene locus groups, significantly more distant metastases are affected by combined LOH. Furthermore, a significantly reduced postmetastatic survival time has been observed in patients with brain metastases affected by synchronous allelic loss at the four breast cancer-associated gene loci. Our results suggest that cumulative LOH of breast cancer-related gene loci is associated with a more aggressive phenotype of metastatic breast tumors.     

Loss of heterozygosity at chromosome 11 in breast cancer: association of prognostic factors with genetic alterations.

We examined DNA from 116 female and four male breast cancer patients for loss of heterozygosity (LOH). DNA was analysed by polymerase chain reaction using ten microsatellite markers on chromosome 11. Three distinct regions of LOH were identified: 11p15.5, 11q13 and 11q22-qter with a LOH frequency of 19, 23 and 37-43% respectively. The marker D11S969 showing the highest frequency of LOH (43%) is located at the 11q24.1-q25 region. No previous molecular genetic studies have shown frequent LOH at the region telomeric to q23 on chromosome 11. Southern analysis revealed that LOH at 11q13 was due to amplification, whereas LOH at 11q22qter was due to deletion. LOH at 11p15.5 was associated with paucity of hormone receptor proteins, high S-phase and positive node status. An association was found between LOH at 11q13 and positive node status. LOH at the 11q22-qter region correlated with a high S-phase fraction. A significant association was found between LOH at 11p15 and chromosome regions 17q21 (the BRCA1 region) and 3p.     

Correlation of allelic losses and clinicopathological factors in 504 primary breast cancers

BACKGROUND: We have defined 18 chromosomal regions in which allelic losses were frequent among breast cancers. We examined whether specific allelic losses might correlate with any clinicopathological factors. METHODS: We tested DNA from matched normal and tumor tissues for loss of heterozygosity (LOH) at 18 microsatellite loci from a cohort of 504 patients who had undergone surgery for breast cancer. RESULTS: LOH at 3p14.3 correlated with a larger size of tumor (greater than 2 cm). LOH at 1p22, 3p25.1, 3p14.3, or 17q21.1 correlated with loss of estrogen receptors. LOH at as many as eleven regions correlated with loss of progesterone receptor, suggesting that these represent general phenomena associated with progression of cancer. Above all, allelic losses at 11q23-24, 13q12, 17p13.3, or 22q13 significantly correlated with lymph-node metastasis (11q23-24, p= 0.0042; 13q12, p=0.0207; 17p13.3, p=0.0478; 22q13, p=0.0162). CONCLUSION: These results suggest that some clinical characteristics of breast cancers are determined by loss of tumor suppressor genes present at specific chromosome regions. Especially, LOH at 11q23-24, 13q12, 17p13.3, and 22q13 is a significant predictor of lymph-node metastasis for patients who have undergone surgery for breast cancer, and may serve as a negative prognostic indicator.     

Mucinous cancers have fewer genomic alterations than more common classes of breast cancer

Mucinous cancers of the breast are distinguished histologically by their abundant pools of mucin and low degree of nuclear pleomorphism. Relative to the more common breast cancers of no distinctive type (ductal carcinoma), mucinous cancers have a relatively favorable prognosis. In a study of chromosomal changes in mucinous cancers, we evaluated the extent of loss of heterozygosity (LOH) at chromosomal regions commonly deleted in usual infiltrating ductal carcinoma, including markers on chromosomal arms 1p, 1q, 3p, 6q, 8p, 9p, 11p, 11q, 13q, 16q, 17p, and 17q. Remarkably, we found an average frequency of LOH of only 1.9 of these 12 chromosomal arms in 18 cases of mucinous carcinoma, compared to an average frequency of LOH of 6.4 of these same chromosomal arms in cases of infiltrating ductal cancer. In three of the 18 cases of mucinous carcinoma studied, including one case with regional lymph node metastases, no LOH was seen at any of the 12 chromosomal regions studied. We considered the possibility of other chromosomal loci being more commonly affected in mucinous cancers and conducted comparative genomic hybridization on six of the cases. These studies demonstrated a low overall frequency of genomic copy number changes (mean of 3.1 changes per case) and failed to reveal any other chromosomal locus with frequent losses that had not been evaluated by microsatellite analysis. Together, these data indicate that mucinous cancers of the breast do not have the extensive genomic alterations that are typically found in more common variants of breast cancer. Thus, mucinous cancers most likely have less genetic instability than most other forms of breast cancer and the molecular pathogenesis of this form of breast cancer is likely to be substantially different than that of usual ductal breast cancer.     

Allelic loss in esophageal squamous cell carcinoma patients with and without family history of upper gastrointestinal tract cancer.

Chromosomal regions with frequent allelic loss may point to major susceptibility genes that will assist in understanding molecular events involved in esophageal carcinogenesis. Esophageal squamous cell carcinoma samples and blood from 46 patients, including 23 patients with and 23 patients without a family history of upper gastrointestinal cancer, were screened using laser microdissected DNA and tested for loss of heterozygosity (LOH) at 18 marker loci representing 14 chromosomal regions (on 2q, 3p, 4p, 4p, 5q, 6q, 8p, 9p, 9q, 11p, 13q, 14q, 15q, and 17p) identified in an earlier genome-wide scan to have frequent LOH. Clinical/pathological and lifestyle risk factor data were also collected. For all 46 tumors combined, the lowest frequency LOH for any of the 18 markers was 37%, and 8 markers showed LOH in > or =75% of informative tumors. One marker (D13S894 on 13q) showed greater LOH in patients with a positive family history (93% versus 50%; P = 0.04), whereas two markers (D6S1027 on 6q and D9S910 on 9q) had significantly more LOH in patients with metastasis, and one marker (D4S2361 on 4p) showed significantly higher LOH in patients with a lower pathological tumor grade. No relation was seen between LOH and lifestyle risk factors. This study confirms the previously observed high frequency LOH for these 14 chromosomal regions, including a locus on 13q where LOH is more common in patients with a family history of upper gastrointestinal cancer than in those without such history, suggesting that a gene in this area may be involved in genetic susceptibility to esophageal cancer.     

Loss of heterozygosity occurs at the D11S29 locus on chromosome 11q23 in invasive cervical carcinoma.

Allelotypic detection of loss of heterozygosity (LOH) has been used to identify putative tumour-suppressor genes. Loci on human chromosome 11q23 are frequently altered in malignant disease, and LOH has been reported at an anonymous D11S29 locus at 11q23 in a proportion of breast and ovarian cancers and malignant melanomas. Previous studies have reported a high frequency of LOH in cervical carcinoma mapping to 11q23. Using polymerase chain reaction techniques employing probes for a recently described polymorphic dinucleotide microsatellite within this locus, we have searched for LOH in 69 cases of invasive cervical carcinoma. Genomic material was microdissected from sections cut from archival paraffin-embedded material, using the patients'' constitutional genotype as a control Sixty-two (90%) of the cases were informative, and LOH occurred in 25/62 (40%) of tumours. Loss of an arm or single chromosome 11 is a well-recognised event in cervical carcinoma, and by employing other microsatellite polymorphisms mapping to 11q13 and 11p11-p12 we excluded those cases with widespread allelic loss. By doing so, LOH at D11S29 was found in 16/53 (30%) of tumours. The findings suggest a putative tumour-suppressor gene on 11q involved in cervical carcinogenesis.     

Alterations of the FHIT gene in breast cancer: association with tumor progression and patient survival.

Our previous results on breast tumors show that LOH (loss of heterozygosity) at the FHIT locus is associated with reduced Fhit protein expression. We have also shown that LOH at this locus is significantly higher in tumors from patients carrying the BRCA2 999de15 mutation than in tumors without this mutation, presumably because of lack of DNA repair. Here, our aim was to determine the relationship of FHIT LOH with breast tumor progression. Five microsatellite markers located within the FHIT gene were typed in 239 breast tumors and corresponding normal tissue, and the LOH results were compared with clinicopathologic factors and LOH at other chromosome regions. LOH at FHIT is associated with estrogen- and progesterone-negative breast tumors, high S-phase fraction, reduced patient survival, and LOH at chromosome regions 6q, 7q, 8p, 9p, 11p, 11q, 13q, 16q, 17p, 17q, 18q, and 20q. A multivariate analysis shows that LOH at FHIT results in a 60% increased relative risk of dying. We conclude that the loss of FHIT results in growth advantage of breast tumor cells, is associated with unstable genome, and may be of prognostic value.     

Allelic deletion at 11q23 is common in MYCN single copy neuroblastomas.

Deletions of the long arm of chromosome 11 (11q) have been noted in primary neuroblastomas, but a comprehensive analysis has not been performed. Therefore, we analysed 331 neuroblastomas (295 sporadic, 15 familial and 21 tumor-derived cell lines) to determine the prevalence of 11q allelic deletions, to map the location of a putative tumor suppressor gene and to perform clinical correlative studies. Assays for loss of heterozygosity (LOH) were performed at 24 microsatellite loci spanning 11q. LOH was observed at multiple 11q loci in 129/295 (44%) sporadic neuroblastomas, 5/15 (33%) familial neuroblastomas, and 5/21 (24%) neuroblastoma cell lines. A single region of 2.1 cM within 11q23.3, flanked by markers D11S1340 and D11S1299, was deleted in all specimens with 11q LOH. Allelic loss at 11q23 was inversely related to MYCN amplification (P<0.001). Within the subset of cases with a single copy of MYCN, 11q LOH was associated with advanced stage disease (P=0.008), unfavorable histopathology (P=0.042), and decreased overall survival probability (P=0.008). However, 11q LOH was not independently prognostic in multivariate analyses. These data support the hypothesis that a tumor suppressor gene mapping within 11q23.3 is commonly inactivated during the malignant evolution of a large subset of neuroblastomas, especially those with unamplified MYCN.     

Screening of selected genomic areas potentially involved in thyroid neoplasms

Loss of heterozygosity (LOH) studies have been used to identify sites harbouring tumour suppressor genes (TSGs) involved in tumour initiation or progression. To further elucidate the genetic mechanisms for follicular and papillary thyroid tumours development, we studied the frequency of LOH in 36 thyroid tumours (21 follicular thyroid adenomas (FAs) and 15 papillary thyroid carcinomas (PTCs)) on 10 specific genomic areas: 3p22, 3p25, 7q21, 7q31, 10q23, 10q25-26, 11q13, 11q23, 13q13 and 17p13.3-13.2 using 20 polymorphic markers. We have selected these areas for two reasons: (a) Even though LOH in thyroid neoplasms has been described in some of these areas, results are controversial, and (b) we have also studied areas described as involved in other epithelial or endocrine tumour types, but not studied up to now in thyroid neoplasms. Two areas showed a high percentage of LOH: 7q31 and 11q23. A 62% LOH was found at 7q31 in the FAs, suggesting, as other authors have proposed, that at least one TSG must be present in the vicinity of the c-met locus. The second area in frequency was at the 11q23 locus, with a 45% LOH in the FAs. This area was studied because it has been described as being involved in the development of epithelial and endocrine cancers. This locus had not been studied before in thyroid neoplasms. This result is interesting because the LOH11CR2A gene is localised at this locus. We suggest that this gene and/or an other TSG nearby may be involved in the progression to FA. In our study, a low percentage of LOH was found in the PTC samples, indicating that TSGs present in the areas we have studied are not significantly involved in their progression. Our data also suggest that TSGs located in areas where no LOH was detected (PTEN, MEN1, Cyclin D1, BRCA2 and RFC3) are not involved or do not have an important role in tumour progression.     

Detailed deletion mapping at chromosome 11q23 in colorectal carcinoma

Loss of heterozygosity (LOH) is frequent at the chromosomal region 11q22-q23 in several types of tumours of diverse cell origin. Previous investigations of LOH at this chromosomal region in colorectal carcinoma have been contradictory in their findings, and have only included between 1-4 loci. In order to define any regions of LOH on 11q23, we investigated 16 loci between D11S940 and D11S934 on the long arm of chromosome 11 using microsatellite analysis. Of 57 colorectal carcinomas specimens, 36 (63.2%) demonstrated LOH at one or more marker, with the highest frequencies of LOH at D11S1340 (41.0%), located between 105.13-111.97 Mb from the centromere, and D11S924 (37.1%) and D11S4107 (40.5%), both located approximately 113 Mb from the centromere. No statistically significant associations between LOH and age-of-presentation or Dukes' stage were found. LOH was observed in colorectal tumours of all Dukes' stages, including Dukes' stages A and B, suggesting that the inactivation of a tumour suppressor gene(s) on 11q23 occurs in the early stages of colorectal carcinoma. These results confirm the presence of putative tumour suppressor gene(s) at chromosome 11q23, involved in the carcinogenesis of colorectal carcinoma, and will facilitate future identification of candidate genes.     

Chromosome alterations and E-cadherin gene mutations in human lobular breast cancer

We have studied a set of 40 human lobular breast cancers for loss of heterozygosity (LOH) at various chromosome locations and for mutations in the coding region plus flanking intron sequences of the E-cadherin gene. We found a high frequency of LOH (100%, 31/31) at 16q21-q22.1. A significantly higher level of LOH was detected in ductal breast tumours at chromosome arms 1p, 3p, 9p, 11q, 13q and 18q compared to lobular breast tumours. Furthermore, we found a significant association between LOH at 16q containing the E-cadherin locus and lobular histological type. Six different somatic mutations were detected in the E-cadherin gene, of which three were insertions, two deletions and one splice site mutation. Mutations were found in combination with LOH of the wild type E-cadherin locus and loss of or reduced E-cadherin expression detected by immunohistochemistry. The mutations described here have not previously been reported. We compared LOH at different chromosome regions with E-cadherin gene mutations and found a significant association between LOH at 13q and E-cadherin gene mutations. A significant association was also detected between LOH at 13q and LOH at 7q and 11q. Moreover, we found a significant association between LOH at 3p and high S phase, LOH at 9p and low ER and PgR content, LOH at 17p and aneuploidy. We conclude that LOH at 16q is the most frequent chromosome alteration and E-cadherin is a typical tumour suppressor gene in lobular breast cancer.     

ATM gene deletion in patients with adult acute lymphoblastic leukemia

BACKGROUND: Loss of heterozygosity (LOH) at the ATM gene (mutated in ataxia telangiectasia [AT] patients) and ATM protein deficiency occur in 14% and 34%, respectively, of patients with chronic lymphocytic leukemia (CLL). ATM protein deficiency also is associated with aggressive disease and worse patient survival. Considering the aberrations in the ATM gene in CLL and the high rate of incidence of lymphoid neoplasias in AT patients, the authors investigated its incidence rate and significance in patients with adult acute lymphoblastic leukemia (ALL). METHODS: Samples from 36 adults with ALL were analyzed for LOH and homozygous deletion (HD) using a panel of three microsatellite markers located at the ATM gene (D11S2179), the MLL gene (D11S1356), and the BCL1 gene (D11S987) loci. These markers are located within the 11q13-q23 locus. RESULTS: Of the 36 informative cases, 10 (28%) showed deletions (7 LOH and 3 HDs) at the D11S2179 marker. In two patients, the deletions were extended to the MLL gene locus. These deletions were submicroscopic because only 3% (1 of 36) of patients showed abnormalities involving 11q23 using cytogenetic studies. The authors also estimated the levels of ATM protein in 15 ALL patients and 12 healthy volunteers by radioimmunoassay. The ATM protein levels in cases with LOH at the ATM gene were between 15-50% of those from normal bone marrow. In contrast to CLL patients, patients with LOH or HD at the ATM gene locus showed better survival compared with patients without ATM gene deletions (P = 0.003). CONCLUSIONS: LOH of the ATM gene and protein deficiency are common in adult ALL, are not demonstrated at the cytogenetic level, and are associated with a favorable prognosis. The authors speculate that ATM deficiency may increase the sensitivity of leukemic blasts to the chemotherapy used during induction and after disease remission in patients with adult ALL. The relatively high frequency of deletion of the D11S2179 marker compared with the D11S1356 marker suggests that ATM is the target gene of the deletion at the 11q23 locus, and that such deletions may play a role in the pathogenesis of ALL.     

Identification of two distinct deletion targets at 11q23 in cutaneous malignant melanoma

Karyotypic and molecular data indicate that genetic alterations of the long arm of chromosome 11 (11q) are involved in the pathogenesis of malignant melanoma as well as of other malignancies. We have shown previously, by analysis of loss of heterozygosity (LOH), that a tumor‐suppressor gene playing an important role in malignant melanoma is likely to be located within a 51‐cM region at 11q23. Its loss appeared to be a late event in tumor progression and an indicator of a less favorable clinical outcome. To further test this hypothesis on a larger set of tumors and to refine the region(s) of common allelic loss, we analyzed 21 polymorphic microsatellite repeats on 11q. A PCR‐based assay for LOH was used to study normal and tumor tissues from 53 individuals with primary cutaneous malignant melanoma or metastatic disease. Our findings indicate that in cutaneous malignant melanoma there are at least 2 distinct regions of common allelic loss on 11q, one of them centered around marker APOC3 at 11q23.1‐q23.2 delineated by markers D11S1347 and D11S4142 and spanning approximately 5 Mb and a second 3‐Mb region around marker D11S925 at 11q23.3 delineated by markers D11S528 and D11S1345. Both regions have been described as deletion targets or as being included within larger allelic deletions detected in several other common tumor types. Thus, these 2 putative melanoma‐suppressor loci are likely to harbor tumor‐suppressor genes relevant to tumorigenesis of melanoma and a number of other common human malignancies. Int. J. Cancer80:205–209, 1999. © 1999 Wiley‐Liss, Inc.     

Deletion mapping of chromosome segment 11q24-q25, exhibiting extensive allelic loss in early onset breast cancer

Frequent allelic deletions at chromosome 11q24-q25 have been described in both early and late onset breast cancers, suggesting the existence of a gene locus implicated in the initiation and/or progression of the disease. In the present study we fine mapped this region further by loss of heterozygosity (LOH) analysis in a population of early onset breast cancer cases (n = 102, 22 to 36 years old). Loss of chromosomal material was assessed for possible association with patient survival as well as Nottingham histologic grade (NHG). Additionally, we investigated the involvement of the 11q24-q25 locus in a group of familial breast cancer cases with no detectable BRCA1 or BRCA2 gene alterations (n = 32, ages 28 to 40 years). Among the consecutive patients, extensive LOH was observed for all markers at 11q24-q25, with frequencies ranging from 42% to 54%. Deletion at the D11S4125 marker was found to be associated with reduced survival (p = 0.026), whereas the adjacent D11S387 marker correlated with higher histologic grade (p = 0.042). In the familial cases, the most telomeric markers showed substantially lower proportions of LOH, ranging from 10% to 21%. Comparison of the two patient groups demonstrated that this difference in LOH frequency was statistically significant for the D11S4098, D11S968, D11S387 and D11S4125 markers (p = 0.020, p = 0.029, p = 0.0070 and p = 0.0030, respectively). We conclude that 11q25 may harbor a gene implicated in early onset breast cancer. Our data suggest that the most probable position for this locus is defined by the markers D11S387 and D11S4125 and furthermore that it may play a less significant role in familial breast cancer cases not linked to either of the BRCA genes.     

Lack of correlation between survival and allele loss on chromosome 7q31–32 in primary breast cancer

High incidence of loss of heterozygosity (LOH), affecting the 7q31–32 chromosome region in sporadic primary human breast carcinomas suggests the presence of a tumor suppressor gene in this region which seems relevant to the development of breast cancer. To further determine the possible role of this region in the pathogenesis of human primary breast cancer and association with survival, LOH analysis was performed on 52 primary breast cancer patients using a set of highly polymorphic microsatellite markers. Our panel contained twenty biopsy cases of unknown survival, nineteen cases with more than five years survival and fourteen cases with less than two years survival. Corresponding normal and tumor DNAs were analyzed by polymerase chain reaction (PCR). The data presented here demonstrate that all patients were informative at least at one locus and 20 (38%) out of 53 cases showed LOH at one or more loci on chromosome 7q31–32. Relatively high incidence of LOH (34%) was detected at the D7S522 microsatellite marker located near to the cMet proto-oncogene while lower frequencies were observed at D7S523 (19%) and D7S495 (17%) loci, supporting the existence of a putative tumor suppressor gene at the chromosome 7q31.1 region. Our results suggest that allelic imbalance on 7q may occur at an early stage of breast carcinogenesis, as no correlation was observed between allelic loss and clinico-pathological data. This work was supported by Hungarian Research Grants ETT (T-019307) and OMFB (04-1-99-94-0328) given to Edith Olah.     

Loss of heterozygosity at chromosome 1p in human breast cancer

232 human primary invasive breast tumors were analyzed with 13 polymorphic microsatellite markers specific to chromosome 1p. Loss of heterozygosity (LOH) was observed in 126 cases or 54% of the tumors. One marker, D1S496, at the 1p35 region showed the highest LOH, 28%. High frequencies of LOH were also detected by the markers, D1S488, D1S167 and D1S435, at the 1p31 region, 25%, 24% and 26% LOH, respectively. This suggests the presence of tumor suppressor genes at these two regions. Tumors with and without LOH at 1p were tested for association with clinico-pathological features of the tumors such as estrogen- and progesterone-receptor content (ER and PgR), age at diagnosis, tumor size, node status, histological type, S-phase fraction, ploidy, survival and LOH at chromosomes 3p, 6q, 9p, 11p, 11q, 13q, 16q, 17p and 17q. A significant association was found between LOH at chromosome 1p and high S-phase fraction and lower survival rate. Association was also found between LOH at 1p and chromosome regions 3p, 6q, 9p and 17q. A multivariate model including prognostic variables, showed that LOH at 1p is an independent prognostic variable and patients who have breast tumors with LOH at 1p have approximately a two-fold increase in relative risk of death. We conclude that screening for 1p deletions gives additional prognostic information that might be useful in breast cancer treatment.     

Molecular genetic alterations on chromosomes 11 and 22 in ependymomas

Ependymomas arise from the ependymal cells at different locations throughout the brain and spinal cord. These tumors have a broad age distribution with a range from less than 1 year to more than 80 years. In some intramedullary spinal ependymomas, mutations in the neurofibromatosis 2 (NF2) gene and loss of heterozygosity (LOH) on chromosome arm 22q have been described. Cytogenetic studies have also identified alterations involving chromosome arm 11q, including rearrangements at 11q13, in ependymomas. We analyzed 21 intramedullary spinal, 14 ventricular, 11 filum terminale and 6 intracerebral ependymomas for mutations in the MEN1 gene, which is located at 11q13, and mutations in the NF2 gene, which is located at 22q12, as well as for LOH on 11q and 22q. NF2 mutations were found in 6 tumors, all of which were intramedullary spinal and all of which displayed LOH 22q. Allelic loss on 22q was found in 20 cases and was significantly more frequent in intramedullary spinal ependymomas than in tumors in other locations. LOH 11q was found in 7 patients and exhibited a highly significant inverse association with LOH 22q (p<0.001). A hemizygous MEN1 mutation was identified in 3 tumors, all of which were recurrences from the same patient. Interestingly, the initial tumor corresponded to WHO grade II and displayed LOH 11q but not yet a MEN1 mutation. In 2 subsequent recurrences, the tumor had progressed to anaplastic ependymoma (WHO grade III) and exhibited a nonsense mutation in exon 10 of MEN1 (W471X) in conjunction with LOH 11q. This suggests that loss of wild-type MEN1 may be involved in the malignant progression of a subset of ependymomas. To conclude, our findings provide evidence for different genetic pathways involved in ependymoma formation and progression, which may allow to define genetically and clinically distinct tumor entities.     

Refinement of the LOH region 1 at 11q23.1 deleted in human breast carcinomas and sublocalization of 11 expressed sequence tags within the refined region

Loss of constitutive heterozygosity at 11q23 has been detected in various human solid tumors. Here, we described the analysis of a series of normal and tumor pairs from 110 breast carcinomas for the presence of loss of heterozygosity at 11q23 loci. The overall frequency of LOH was 48%, confirming the importance of deletions at 11q23 in breast tumorigenesis. Previously, we have identified two independent regions of LOH at 11q23, the LOH region 1 at 11q23.1 and the LOH region 2 at 11q23.3. The most telomeric region was recently refined between loci D11S1345 and D11S1316, a region of about 1 Mb. However, the LOH region 1, most centromeric, was still not finely refined: the boundaries were defined by loci D11S2000 and D11S897, separated by about 8 Mb. Here, we refined its boundaries between loci D11S1347 and D11S927, a region of about 2 Mb. We have mapped 11 expressed sequence tags (ESTs) within this region and excluded another 20. This study represents a further step toward the identification of the putative tumor suppressor gene found within the LOH region 1 at 11q23.1.