Louise C. Strong

A single nucleotide polymorphism in the MDM2 promoter attenuates the p53 tumor suppressor pathway and accelerates tumor formation in humans

The tumor suppressor p53 gene is mutated in minimally half of all cancers. It is therefore reasonable to assume that naturally occurring polymorphic genetic variants in the p53 stress response pathway might determine an individuals susceptibility to cancer. A central node in the p53 pathway is the MDM2 protein, a direct negative regulator of p53. In this report, a single nucleotide polymorphism (SNP309) is found in the MDM2 promoter and is shown to increase the affinity of the transcriptional activator Sp1, resulting in higher levels of MDM2 RNA and protein and the subsequent attenuation of the p53 pathway. In humans, SNP309 is shown to associate with accelerated tumor formation in both hereditary and sporadic cancers. A model is proposed whereby SNP309 serves as a rate-limiting event in carcinogenesis.

Wild-type p53 restores cell cycle control and inhibits gene amplification in cells with mutant p53 alleles.

Loss of cell cycle control and acquisition of chromosomal rearrangements such as gene amplification often occur during tumor progression, suggesting that they may be correlated. We show here that the wild-type p53 allele is lost when fibroblasts from patients with the Li-Fraumeni syndrome (LFS) are passaged in vitro. Normal and LFS cells containing wild-type p53 arrested in G1 when challenged with the uridine biosynthesis inhibitor PALA and did not undergo PALA-selected gene amplification. The converse occurred in cells lacking wild-type p53 expression. Expression of wild-type p53 in transformants of immortal and tumor cells containing mutant p53 alleles restored G1 control and reduced the frequency of gene amplification to undetectable levels. These studies reveal that p53 contributes to a metabolically regulated G1 check-point, and they provide a model for understanding how abnormal cell cycle progression leads to the genetic rearrangements involved in tumor progression.

Gain of Function of a p53 Hot Spot Mutation in a Mouse Model of Li-Fraumeni Syndrome

Individuals with Li-Fraumeni syndrome carry inherited mutations in the p53 tumor suppressor gene and are predisposed to tumor development. To examine the mechanistic nature of these p53 missense mutations, we generated mice harboring a G-to-A substitution at nucleotide 515 of p53 (p53+/515A) corresponding to the p53R175H hot spot mutation in human cancers. Although p53+/515A mice display a similar tumor spectrum and survival curve as p53+/- mice, tumors from p53+/515A mice metastasized with high frequency. Correspondingly, the embryonic fibroblasts from the p53515A/515A mutant mice displayed enhanced cell proliferation, DNA synthesis, and transformation potential. The disruption of p63 and p73 in p53-/- cells increased transformation capacity and reinitiated DNA synthesis to levels observed in p53515A/515A cells. Additionally, p63 and p73 were functionally inactivated in p53515A cells. These results provide in vivo validation for the gain-of-function properties of certain p53 missense mutations and suggest a mechanistic basis for these phenotypes.

Bone sarcomas linked to radiotherapy and chemotherapy in children

We estimated the risk of subsequent bone cancer among 9170 patients who had survived two or more years after the diagnosis of a cancer in childhood. As compared with the general population, the patients had a relative risk of 133 (95 percent confidence interval, 98 to 176) and a mean (+/- SE) 20-year cumulative risk of 2.8 +/- 0.7 percent. Detailed data on treatment were obtained on 64 patients in whom bone cancer developed after childhood cancer. As compared with 209 matched controls who had survived cancer in childhood but who did not have bone cancer later, patients who had had radiation therapy had a 2.7-fold risk (95 percent confidence interval, 1.0 to 7.7) and a sharp dose-response gradient reaching a 40-fold risk after doses to the bone of more than 6000 rad. The relative dose-response effect among patients who had been treated for retinoblastoma resembled that among patients with all other types of initial tumors, although the cumulative risk of bone cancer in the retinoblastoma group was higher. Similar numbers of patients were treated with orthovoltage and megavoltage; the patterns of risk among categories of doses did not differ according to the type of voltage. After adjustment for radiation therapy, treatment with alkylating agents was also linked to bone cancer (relative risk, 4.7; 95 percent confidence interval, 1.0 to 22.3), with the risk increasing as cumulative drug exposure rose. We conclude that both radiotherapy and chemotherapy with alkylating agents for childhood cancer increase the subsequent risk of bone cancer.

Sequence analysis of BRCA1 and BRCA2: correlation of mutations with family history and ovarian cancer risk.

PURPOSE Previous studies of mutations in BRCA1 or BRCA2 have used detection methods that may underestimate the actual frequency of mutations and have analyzed women using heterogeneous criteria for risk of hereditary cancer. PATIENTS AND METHODS A total of 238 women with breast cancer before age 50 or ovarian cancer at any age and at least one first- or second-degree relative with either diagnosis underwent sequence analysis of BRCA1 followed by analysis of BRCA2 (except for 27 women who declined analysis of BRCA2 after a deleterious mutation was discovered in BRCA1). Results were correlated with personal and family history of malignancy. RESULTS Deleterious mutations were identified in 94 (39%) women, including 59 of 117 (50%) from families with ovarian cancer and 35 of 121 (29%) from families without ovarian cancer. Mutations were identified in 14 of 70 (20%) women with just one other relative who developed breast cancer before age 50. In women with breast cancer, mutations in BRCA1 and BRCA2 were associated with a 10-fold increased risk of subsequent ovarian carcinoma (P = .005). CONCLUSION Because mutations in BRCA1 and BRCA2 in women with breast cancer are associated with an increased risk of ovarian cancer, analysis of these genes should be considered for women diagnosed with breast cancer who have a high probability of carrying a mutation according to the statistical model developed with these data.

Early menopause in long-term survivors of cancer during adolescence

Objective: We attempted to investigate the risk of early menopause after treatment for cancer during childhood or adolescence. Study Design: We interviewed 1067 women in whom cancer was diagnosed before age 20, who were at least 5-year survivors, and who were still menstruating at age 21. Self-reported menopause status in survivors was compared with that in 1599 control women. Results: Cancer survivors, with disease diagnosed between ages 13 and 19, had a risk of menopause four times greater than that of controls during the ages 21 to 25; the risk relative to controls declined thereafter. Significantly increased relative risks of menopause during the early 20s occurred after treatment with either radiotherapy alone (relative risk 3.7) or alkylating agents alone (relative risk 9.2). During ages 21 to 25 the risk of menopause increased 27-fold for women treated with both radiation below the diaphragm and alkylating agent chemotherapy. By age 31, 42% of these women had reached menopause compared with 5% for controls. Conclusions: Treatment for cancer during adolescence carries a substantial risk for early menopause among women still menstruating at age 21. Increasing use of radiation and chemotherapy, together with the continued trend toward delayed childbearing, suggests that these women should be made aware of their smaller window of fertility so that they can plan their families accordingly.

The Childhood Cancer Survivor Study: A National Cancer Institute–Supported Resource for Outcome and Intervention Research

Survival for childhood cancer has increased dramatically over the last 40 years with 5-year survival rates now approaching 80%. For many diagnostic groups, rapid increases in survival began in the 1970s with the broader introduction of multimodality approaches, often including combination chemotherapy with or without radiation therapy. With this increase in rates of survivorship has come the recognition that survivors are at risk for adverse health and quality-of-life outcomes, with risk being influenced by host-, disease-, and treatment-related factors. In 1994, the US National Cancer Institute funded the Childhood Cancer Survivor Study, a multi-institutional research initiative designed to establish a large and extensively characterized cohort of more than 14,000 5-year survivors of childhood and adolescent cancer diagnosed between 1970 and 1986. This ongoing study, which reflects the single most comprehensive body of information ever assembled on childhood and adolescent cancer survivors, provides a dynamic framework and resource to investigate current and future questions about childhood cancer survivors.

Germline Mutations of the p53 Tumor-Suppressor Gene in Children and Young Adults with Second Malignant Neoplasms

BACKGROUND Acquired mutations in the p53 tumor-suppressor gene have been detected in several human cancers, including colon, breast, and lung cancer. Inherited mutations (transmitted through the germline) of this gene can underlie the Li-Fraumeni syndrome, a rare familial association of breast cancer in young women, childhood sarcomas, and other malignant neoplasms. We investigated the possibility that p53 mutations in the germline are associated with second primary cancers that arise in children and young adults who would not be considered as belonging to Li-Fraumeni families. METHODS Genomic DNA was extracted from the blood leukocytes of 59 children and young adults with a second primary cancer. The polymerase chain reaction, in combination with denaturant-gel electrophoresis and sequencing, was used to identify p53 gene mutations. RESULTS Mutations of p53 that changed the predicted amino acid sequence were identified in leukocyte DNA from 4 of the 59 patients (6.8 percent). In three cases, the mutations were identical to ones previously found in the p53 gene. The fourth mutation was the first germline mutation to be identified in exon 9, at codon 325. Analysis of leukocyte DNA from close relatives of three of the patients indicated that the mutations were inherited, but cancer had developed in only one parent at the start of the study. CONCLUSIONS These findings identify an important subgroup of young patients with cancer who carry germline mutations in the p53 tumor-suppressor gene but whose family histories are not indicative of the Li-Fraumeni syndrome. The early detection of such mutations would be useful not only in treating these patients, but also in identifying family members who may be at high risk for the development of tumors.

Characterization of BRCA1 and BRCA2 Mutations in a Large United States Sample

PURPOSE An accurate evaluation of the penetrance of BRCA1 and BRCA2 mutations is essential to the identification and clinical management of families at high risk of breast and ovarian cancer. Existing studies have focused on Ashkenazi Jews (AJ) or on families from outside the United States. In this article, we consider the US population using the largest US-based cohort to date of both AJ and non-AJ families. METHODS We collected 676 AJ families and 1,272 families of other ethnicities through the Cancer Genetics Network. Two hundred eighty-two AJ families were population based, whereas the remainder was collected through counseling clinics. We used a retrospective likelihood approach to correct for bias induced by oversampling of participants with a positive family history. Our approach takes full advantage of detailed family history information and the Mendelian transmission of mutated alleles in the family. RESULTS In the US population, the estimated cumulative breast cancer risk at age 70 years was 0.46 (95% CI, 0.39 to 0.54) in BRCA1 carriers and 0.43 (95% CI, 0.36 to 0.51) in BRCA2 carriers, whereas ovarian cancer risk was 0.39 (95% CI, 0.30 to 0.50) in BRCA1 carriers and 0.22 (95% CI, 0.14 to 0.32) in BRCA2 carriers. We also reported the prospective risks of developing cancer for cancer-free carriers in 10-year age intervals. We noted a rapid decrease in the relative risk of breast cancer with age and derived its implication for genetic counseling. CONCLUSION The penetrance of BRCA mutations in the United States is largely consistent with previous studies on Western populations given the large CIs on existing estimates. However, the absolute cumulative risks are on the lower end of the spectrum.

Germline p53 Mutations in a Cohort with Childhood Sarcoma: Sex Differences in Cancer Risk

To characterize cancer risk in heterozygous p53 mutation carriers, we analyzed cancer incidence in 56 germline p53 mutation carriers and 3,201 noncarriers from 107 kindreds ascertained through patients with childhood soft-tissue sarcoma who were treated at the University of Texas M. D. Anderson Cancer Center. We systematically followed members in these kindreds for cancer incidence for >20 years and evaluated their p53 gene status. We found seven kindreds with germline p53 mutations that include both missense and truncation mutation types. Kaplan-Meier analysis showed similar cancer risks between 21 missense and 35 truncation p53 mutation carriers (log-rank chi(2)=0.04; P=.84). We found a significantly higher cancer risk in female carriers than in male carriers (log-rank chi(2)=12.1; P<.001), a difference not explained by an excess of sex-specific cancer. The calculated standardized incidence ratio (SIR) showed that mutation carriers had a risk for all types of cancer that was much higher than that for the general population (SIR = 41.1; 95% confidence interval [CI] 29.9-55.0) whereas noncarriers had a risk for all types of cancer that was similar to that in the general population (SIR = 0.9; 95% CI 0.8-1.0). The calculated SIRs showed a >100-fold higher risk of sarcoma, female breast cancer, and hematologic malignancies for the p53 mutation carriers and agreed with the findings of an earlier segregation analysis based on the same cohort. These results quantitatively illustrated the spectrum of cancer risk in germline p53 mutation carriers and will provide valuable reference for the evaluation and treatment of patients with cancer.