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N Janin

Publications and source records attributed to N Janin.

At least 19 recordsLinked to original sources
PubMed2001

Cancer risk in heterozygotes for ataxia-telangiectasia.

Epidemiological studies have suggested that ataxia-telangiectasia (AT) heterozygotes have a predisposition to cancer, especially breast cancer in women. Now, haplotyping can identify heterozygotes for AT mutation (ATM) in AT families, allowing the risk of cancer associated with ATM heterozygosity status to be better assessed. We report a family study of AT patients, in which we estimated the risk of cancer according to ATM heterozygosity status. We analyzed demographic characteristics and occurrence of cancer in 1,423 relatives of AT patients. Haplotyping was performed in living relatives. The probability of being heterozygotes for ATM was calculated for deceased relatives. The risk of developing cancer was estimated in the cohort of relatives, and expected numbers of cancer cases were calculated from French age period-specific incidence rates. The number of cancers at all sites in the total population of relatives was not higher than expected. However, significant heterogeneity was found according to ATM heterozygosity status. This is mainly due to the increased risk of breast cancer previously observed in obligate heterozygotes. In obligate heterozygotes, relative risk (RR) was non-significantly increased for thyroid cancer, leukemia and liver cancer. Risks of ovarian, lung, pancreatic, kidney, stomach and colorectal cancers were non-significantly increased in the group with 0.5 probability of being heterozygotes. The RR was not significantly increased for any site of cancer, except for breast. Therefore, there is no evidence that specific screening of relatives of AT patients would be justified at particular sites other than the breast. However, the amplitude of the risk of breast cancer estimated in heterozygous women does not appear to justify a separate screening program from that already available to women with a first-degree relative affected by breast cancer.

Ataxia Telangiectasia↗
PubMed2001

The R71G BRCA1 is a founder Spanish mutation and leads to aberrant splicing of the transcript.

In a BRCA1 screening in familial breast cancer carried out in different centres in Spain, France, and United Kingdom, a missense mutation 330A>G which results in a Arg to Gly change at codon 71 (R71G) was independently identified in 6 families, all of them with Spanish ancestors. This residue coincides with the -2 position of the exon 5 donor splice site. We further investigated the effect of this base substitution on the splicing of BRCA1 mRNA. The sequence analysis of the cDNA indicated that 22 bp of exon 5 were deleted, creating with the first bases of exon 6 a termination codon at position 64, which results in a truncated protein. The BRCA1 haplotype of the R71G carrier patients and Spanish controls was analysed by use of six microsatellites located within or near BRCA1. Our results are consistent with the possibility that these families shared a common ancestry with BRCA1 R71G being a founder mutation of Spanish origin.

Age of Onset↗
PubMed2000

A simple model for carcinogenesis of colorectal cancers with microsatellite instability.

Lynch syndrome is a hereditary predisposition to colorectal cancer (CRC) and other cancers caused by germline mutations in mismatch repair (MMR) genes. Almost all the cancers diagnosed in Lynch syndrome have an acquired MMR deficiency, a replication error (RER) mutator phenotype that is also found in a minority of sporadic cancers developed in the target organs of Lynch syndrome. Lynch syndrome displays many curious features that cannot be accounted for by the prevailing concepts of carcinogenesis and genetics: (1) CRCs occur preferentially in the right side of the colon, whereas the majority of sporadic cases develop in the left colon; (2) the increased risk of CRC is not associated with an increased incidence of adenomatous polyps, which are necessary precancerous lesions in the development of common CRCs; (3) the tumor spectrum in Lynch syndrome is restricted to the colon and some extracolonic sites, whereas the responsible MMR genes are ubiquitously expressed; (4) the tumor risk, which is negligible during childhood, becomes significant during adulthood at the age of 25 and thereafter remains essentially constant throughout the ages. (5) Finally, the sporadic counterparts to the CRCs diagnosed in the setting of Lynch syndrome very curiously develop almost exclusively in the right colon, whereas this right-sidedness is much less pronounced in Lynch syndrome. To explain these anomalies, we propose a model of RER+ carcinogenesis based on the simple idea that the RER mutator phenotype has only short-term viability in normal cells. The proposed model states that the RER+ carcinogenesis is divided into two clearly distinct evolutive phases: (1) a preliminary phase starting with the counter-selective loss of mismatch repair function, in which most clones with the RER mutator phenotype are eliminated through apoptosis or an accelerated aging process; (2) an explosive phase that is initiated only if mutations blocking apoptosis and senescence, rapidly acquired during the short life span of the nontransformed RER+ clones, eventually rescue one RER+ cell that gives rise to the malignant clone. It will be shown that this theoretical framework with its heterodox initiation process not only possesses the virtue of allowing an understanding of Lynch syndrome, but may also have broader applications to all research fields dealing with carcinogenesis.

Animals↗
PubMed2000

[Radiotherpay and immediate breast reconstruction with myocutaneous flap in breast cancer of reserved prognosis].

In France, immediate breast reconstruction (IBR) for infiltrating carcinoma remains controversial. Many teams advocate the possible event of a post mastectomy radiotherapy and its negative effect on IBR. In our Institute we do not exclude infiltrating breast cancer patient from IBR. In the poor prognostic patients who wish IBR, we recommend autologous IBR to obtain the best aesthetic result with minimum revision procedures and best tolerance to adjuvant radiotherapy. From January 1993 to December 1997, we performed 687 IBR with myocutaneous flap for infiltrating carcinomas. In this group only 68 patients needed postoperative chest wall radiotherapy (45 Gy): 27 TRAM flap, 41 latissimus flap. Only one of the TRAM but 39 of latissimus flaps were associated with a prosthesis. The mean follow-up was 24 months. Fourteen patients developed metastatic disease, and ten were dead at the time of the chart revue. The autogenous TRAM flap tolerate radiation quite well and remain soft and mobile. The latissimus flap associated with a prosthesis developed capsular contracture (BAKER II or III) in 71% of cases. In all cases the cosmetic impairment was not important and the result after capsulectomy remained soft. We concluded that IBR could be offered to motivated patients in all stages of the disease regardless of the subsequent chest wall radiotherapy, and we recommend its use for possible autologous reconstruction.

Adult↗
PubMed1999

[Explanation of enigmas of the Lynch syndrome thanks to a new carcinogenesis model characterized by an unorthodox initiation process].

The genotype-phenotype relationship of Lynch syndrome displays many enigmatic features which cannot be explained satisfactorily by the prevailing concepts of carcinogenesis and genetic predisposition to cancer. We propose here a new model of carcinogenesis divided into two and only two evolutive phases: a) a preliminary phase starting with the counter-selective loss of mismatch repair function, in which most clones with the RER mutator phenotype are eliminated through apoptosis or an accelerated ageing process; b) an explosive phase that is initiated only if mutations blocking apoptosis and senescence, rapidly acquired during the short life span of the non-transformed RER+ clones, eventually rescue one mismatch repair-deficient cell that gives rise to the malignant clone. Carcinogenesis is proposed here to progress irreversibly and very rapidly once initiated. We shall show how this model provides a meaningful etiologic and pathogenic interpretation of all the curious features of Lynch syndrome.

Adenoma↗
PubMed1999

Breast cancer risk in ataxia telangiectasia (AT) heterozygotes: haplotype study in French AT families.

Epidemiological studies in ataxia telangiectasia (AT) families have suggested that AT heterozygotes could have an increased cancer risk, especially breast cancer (BC) in women. It has also been suggested that an increased sensibility of AT heterozygotes to the effect of ionizing radiation could be responsible for the increased BC risk. BC relative risk (RR) estimation in AT heterozygotes within families ascertained through AT children is presented here. Family data collected included demographic characteristics, occurrence of cancers, past radiation exposures and blood samples. DNA samples were studied using seven ATM linked microsatellites markers allowing AT haplotypes reconstitution. The relative risk of BC was assessed using French estimated incidence rates. A significant increase risk of BC is found among obligate ATM heterozygotes with a point estimate of 3.32 (P = 0.002). BC relative risk calculated according to age is significantly increased among the obligate ATM heterozygotes female relatives with an age < or = 44 years (RR = 4.55, P = 0.005). The BC relative risk is statistically borderline among the obligate ATM heterozygote female relatives with an age > or = 45 years (RR = 2.48, P = 0.08). The estimated BC relative risk among ATM heterozygotes is consistent with previously published data. However, the increased risk is only a little higher than classical reproductive risk factors and similar to the risk associated with a first-degree relative affected by BC.

Adolescent↗
PubMed1996

[20 years of progress in dissecting mechanisms of oncogenesis. Relations between magic of science and requirements of medicine].

In the last twenty years, our understanding of carcinogenesis has evolved from a description of the natural history of cancer development, a conception inherited from Darwin, to the dissection of the underlying molecular mechanisms leading to phenotypic changes in cells, a neodarwinian interpretation. Most scientists agree that random germ cell mutations enhancing cell survival and reproduction capacities play a major role in the evolution of species and that carcinogenesis progresses from acquisition of genetic anomalies which alter the normal function of oncogens or antioncogens. Since the discovery of src, the first oncogen to be identified twenty years ago, and more recently the discovery of antioncogens such as p53, hopes and expectations have grown steadily, and passionately, often far beyond reason dietated by the real world of clinical medicine. Yet curiously, many clinicians hesitate to express one essential point: advances in science and technology, is not equivalent to advances in medicine. It is our responsibility to resist the illusion of progress, for this illusion turns out to have a negative impact in our patients. To paraphrase the French philosopher André Comte-Sponville, the power conferred by the exercise of medicine is not based solely on scientific knowledge, but also on human compassion.

Humans↗
PubMed1996

Circulating anti-p53 antibodies in esophageal cancer patients are found predominantly in individuals with p53 core domain mutations in their tumors.

Serum antibodies reacting with the tumor suppressor protein p53 have been detected previously in cancer patients with a variety of neoplasms. Two initial (although insufficient) prerequisites for a B-cell response to occur have been proposed: p53 protein accumulation in the tumor or a mutant p53 gene, or both. We have examined 65 esophageal cancer cases (42 from Guangzhou and Shenyang, People's Republic of China, and 23 from Paris, France) to obtain a prevalence estimate of anti-p53 antibodies for this type of cancer and to define the relationship of p53 tumor status to B-cell immune response. Sera were analyzed in a triplicate assay (enzyme-linked immunoassay, immunoprecipitation, and immunoblot) for anti-p53 antibodies. Tumor DNA was screened for mutations in exons 5-8, and tumor tissue was examined by immunohistochemistry for abnormal p53 protein accumulation. p53 mutations were found in 36 (58%) of 62 cases analyzed. Sixteen patients (25%) had circulating antibodies to the tumor suppressor protein. All but two (88%) of the tumors from seropositive cases had a mutation in the DNA binding region of the p53 gene, and with one exception, these tumors also showed nuclear accumulation of the p53 protein. In contrast, tumor mutations were found in just 22 (46%) of the 48 individuals in whom we did not detect anti-p53 antibodies. Among the 22 seronegative cases for which we found no tumor mutations, 11 revealed p53 protein accumulation by immunohistochemical analysis. Thus, circulating anti-p53 antibodies may be present in one-fourth of esophageal cancer patients, most of whom also would be expected to have a p53 gene mutation in their tumors. Patients without such mutations appear considerably less likely to mount a B-cell response to the p53 tumor suppressor protein than those that do (P < 0.01).

Adult↗
PubMed1996

Truncation at conserved terminal regions of BRCA1 protein is associated with highly proliferating hereditary breast cancers.

The existence of two subgroups of BRCA1-associated breast cancer (BC) families has been recently posited: the first with highly proliferating tumors, and the second composed of cases with a low proliferation rate. Our aim was to test whether the proliferation rate of BRCA1-associated breast cancers was affected by the site of the germ line mutation in the BRCA1 gene. We analyzed the distribution of the mitotic index, a histoprognostic grade component shown to segregate in families, matching for germ line mutation location in a series of 28 breast cancers from 20 kindreds. We observed a prevalence of highly proliferating tumors when the mutation occurs in the two terminal conserved domains of the BRCA1 protein, ie., in the amino and carboxyl termini (P = 0.0024). Our data provide evidence for a genotype-phenotype correlation and along with their strong conservation during evolution argue for the importance of these two regions in the control of mammary cell growth.

Alleles↗
PubMed1996

Deregulated apoptosis in ataxia telangiectasia: association with clinical stigmata and radiosensitivity.

Ataxia telangiectasia (AT) is a recessive genetic disease featuring neurodegeneration, immunodeficiency, chromosomal instability, radiation hypersensitivity, and increased predisposition to cancer. Reduced or delayed induction of the tumor suppressor protein p53 after gamma -irradiation was reported. These characteristics may be compatible with an inability to correctly regulate apoptosis. We show here that AT lymphocytes and EBV-transformed lymphoblasts demonstrate a significantly higher level of spontaneous apoptosis, whereas ionizing radiation-induced apoptosis is reduced compared to normal cells. However, neither AT nor normal primary fibroblasts undergo apoptosis after irradiation. Consequently, we conclude that the radiosensitivity of the AT cells is not related to an increased apoptotic response. Finally, we show that SV40-transformed AT fibroblasts undergo gamma- ray-induced apoptosis, while SV40-transformed normal cells do not. This result raises the question of the physiological relevance of the latter cellular model with respect to the AT phenotype.

Apoptosis↗
PubMed1995

Primary proliferative T cell response to wild-type p53 protein in patients with breast cancer.

Mutations in the p53 tumor suppressor gene are the most frequent genetic alterations found in human tumors. There are mainly point mutations that lead to single amino acid substitutions. The mutated proteins have a longer half-life than wild-type p53 and accumulate in the nucleus of tumor cells. Anti-p53 antibodies have been found in sera of patients with several types of cancers including breast cancer. This report describes a T cell immune response in three patients with breast tumors who had mutated p53 gene and accumulated p53 protein. All showed a humoral response to p53 protein and the T cells of these patients recognized the wild-type p53 protein and proliferated in response to it. The data reported here are relevant to the immune processes leading to autoimmunity and have a bearing on anti-p53 vaccine development in tumor immunology.

Antibodies↗
PubMed1995

[Genetic predisposition to cancer].

This review focuses on the genetics of inborn predisposition to the development of cancer. The gene defects responsible for the majority of the most common syndromes of inherited predisposition to cancer have been deciphered during the last five years. These discoveries have shown that the genetics of most of these inherited forms of cancer is remarkably simple: the mechanism underlying the risk of cancer is precisely the one proposed by Knudson to explain the inherited forms of retinoblastoma. Only a small minority of the cancers are imputable to inherited mutations causing a very high risk of cancer. However, low penetrance susceptibility genes, mainly acting as environmental risk modifiers, are probably involved in the development of the majority of cancers. As much as possible, we will consider the immediate and long term possible repercussions on everyday medical practice of these advances in basic understanding of genetic cancer risks.

Genetic Counseling↗