The first full day opened with a session on basic biology of the breast. Dr. Jose Russo, Fox Chase Cancer Center, Philadelphia, led off with a discussion on the cellular basis of the breast's susceptibility to carcinogenesis. The Russo group's work on rodents has elaborated the theme that the state of mammary duct differentiation is inversely correlated with sensitivity to chemical carcinogens. Consistent with this notion are epidemiological data showing that, in humans, pregnancy and lactation (with the associated cell differentiation) are protective against the cancer. Russo's new studies demonstrated that virgin rats treated with human chorionic gonadotropin (HCG), the pregnancy hormone, have a lower incidence of tumorigenisis than untreated rats. Moreover, HCG treatment enhanced mammary cell differentiation.

Drs. Marc E. Lippman, Georgetown University Medical Center, Washington, D.C., and C. Kent Osborne, University of Texas Health Science Center, San Antonio, discussed their ongoing studies on key membrane receptors (members of the erbB and her2/neu families) whose expression is often elevated in breast cancer. Osborne reported that elevated her2/neu expression in the cancer is associated specifically with failure to respond to traditional (tamoxifen) hormonal treatment. Both investigators emphasized the need for developing cancer cell-specific targeting mechanisms. To this end, Lippman reported on their progress in developing antibodies and antisense therapeutics targeted to the membrane receptor gene products.

Charles W. Daniel, Department of Biology, Sinsheimer Laboratories, University of California at Santa Cruz, pursued the theme of biomarkers that distinguish normal and malignant cells. Studies in his lab have demonstrated that certain genes in homeotic regulatory class Iroquois are normally expressed in luminal epithelial cells (the precursors for the vast majority of breast cancers) but not in myoepithelial cells. In cancers, he noted, there is often misexpression of members of this gene class.

As is often the case at biomedical meetings, one or two newly identified genes dominate the program. Not surprisingly, the hot sister molecules of this meeting were the BRCA (for breast cancer) 1 and 2 genes and their protein products. Talks on the topic began in the session on breast cancer tumor suppressor genes. Mutations in BRCA 1 or 2 are clearly associated with a subset of familial predisposition to breast, ovarian, colon, and prostate cancer. P. Andrew Futreal, Duke University Medical Center, Durham, N.C., extended these findings by presenting evidence that families with unique cancer patterns often demonstrated BRCA 1 or 2 gene deletions and/or RNA splice variants. Moreover, he noted a higher frequency of mutations in early-onset breast cancer families. But his data do show that not all familial breast cancer is associated with mutated BRCA 1 or 2, leading his group and others to hunt for additional BRCA genes.

Simon Gayther, Addenbrooke's Hospital, Cambridge, UK, spoke on the relative contribution of mutations in three parts of each gene to breast vs. ovarian cancer. Truncations in the first two-thirds of the gene are related to ovarian cancer risk, while truncations in the last third are related to breast cancer. Families with high risk for ovarian cancer have mutations in the central "ovarian cancer cluster" region. No comparable clusters are seen in BRCA 2 for male breast cancer.

Evan R. Simpson, University of Texas Southwestern Medical Center, Dallas, the session's final speaker, departed from the BRCA issue to discuss mesenchymal-epithelial interaction and the role of locally produced estrogens in mammary tissue. He noted that aromatase (CYP19), which converts androgens to estrogen, is expressed in breast, adipose, and tumor tissue, evidently more in mesenchymal cells. This activity increases with age in both males and females. Simpson suggested that aromatase activity is highest in the quadrant of the breast that contains a tumor and higher in breasts of cancer versus non-cancer patients. He proposed that tumors express cytokines that stimulate aromatase.

In a session focusing on how breast cells become immortalized, Jerry Shay, University of Texas at Dallas, focused on the multistep nature of this event. He advanced the theory that the first stage of cell senescence involves loss of the tumor suppressor p53 and pRB function. These cells can be maintained, and if telomere shortening is followed by telomerase activation, cell immortalization occurs. PCR methods (TRAP assay) are being used in his lab to follow the shortening of telomeres in successive cell passages (from 17 to 1 kB) in human mammary epithelial cells. Telomerase activity (TA) was detected in all stages of this cancer including carcinoma in situ, but not in normal mammary tissue. Means of blocking TA in breast cancers are now being studied. Nonetheless, Shay emphasized the lack of generalities that can be made regarding TA since, in certain other cancers, TA is seen only after the cancer is established. Moreover, some normal tissues have TA and not all tumors (e.g., neuroblastoma) have TA.

Martha R. Stampfer, also of Lawrence Berkeley Laboratory, spoke on the cellular changes observed in human mammary epithelial cell (HMEC) lines derived from serial passage of normal HMECs in the presence of the chemical carcinogen benzpyrene. In contrast to normal cells, clones selected from the benzpyrene-treated lines grew in presence of transforming growth factor beta (TGFbeta). As they became immortal, these clonal lines showed loss of p16, possibly a loss of p53, and a shortening of telomere length. Telomerase activity increased in later passages and telomere length stabilized. Stampfer noted that telomere truncation in certain stages of growth alters expression of genes proximal to the telomeres.

The influence of estrogen on breast cancer remains a concern among researchers and clinicians. Therefore, Kenneth Korach of the National Institute of Environmental Health Sciences, Research Triangle Park, N.C., and his colleagues have generated estrogen receptor knockout (ERKO) mice. These animals, lacking a functional ER-alpha gene, provide a model for discriminating the role of ER-alpha from that of the newly discovered ER-beta, another nuclear ligand-activated transcription factor, and from possible cell membrane effects of estrogen. Not surprisingly, in the ERKO mice, mammary glands are primitive and there is no ductal development, even in the presence of estrogen. This group has now begun to evaluate the interaction between ER-alpha and the oncogene WNT1. Korach reported that ER-alpha wild-type mice that do have WNT1 frequently show mammary ductal hyperplasia, and have many mammary tumors in both male and female animals. ERKO/WNT1^- mice have only vestigial glands with small ducts.. In contrast, approximately 25% of the ERKO mice that overexpress the WNT1 transgene did form tumors; here tumor growth was delayed compared to that in the ER-alpha wild-type/WNT1⁺. These findings indicate that expression of the ER-alpha gene contributes to mammary tumor formation, but is not essential for tumor development.

In the afternoon of Day 3, the issue of BRAC 1 function was considered. A representative from David Livingston's lab (Dana-Farber Cancer Institute, Boston) presented evidence for the protein's role as a cell cycle regulator and DNA stabilizer. The paper given by Frank Calzone of Amgen Inc., Thousand Oaks, Calif., demonstrated that the BRCA 1 splice isoform containing exon 11 localizes and functions in the nucleus. In contrast, BRCA 1 lacking this large exon is found in the cytoplasm. Because the BRCA 1 isoform lacking exon 11 is found in normal as well as cancer cells, it may have a cytoplasmic function.

Both Roger Wiseman, NIEHS, and Lewis A. Chodosh, University of Pennsylvania School of Medicine, Philadelphia, noted that in embryos BRCA 1 was present in rapidly differentiating and proliferating tissues. In adults, expression of both BRCA 1 and BRCA 2 in mammary tissues is more pronounced than at puberty in non-parous adult mice. BRCA 1 expression is high in mammary tissue of pregnant mice, possibly due to high levels of circulating estrogen and progesterone. These observations prompted J. Russo to point out that BRCA may govern development of the mammary gland. Studies in the Russo lab have found that women carrying a BRCA 1 mutation often have different patterns of mammary gland development than do women with wild-type BRCA 1.

The issue of possible dominant negative forms of BRCA 1 was considered in Wiseman's presentation. He pointed out that none have been found, possibly because mutations so far identified are missense mutations and truncations, all of which lead to loss of function.

Dealing with the topic of diet, nutrition, and breast cancer, Walter Willett of the Harvard School of Public Health, Boston, presented the current status of the breast cancer-dietary fat issue: this is not now accepted as a risk factor based on epidemiologic findings; indeed certain kinds of fat, such as olive oil, may be protective. The best established dietary risk factor is alcohol intake, which appears to increase risk for breast cancer even among moderate drinkers. In consideration of the dietary fat hypothesis, a strong argument was made that overall elevated energy intake may constitute risk, inasmuch as greater nutrition can be linked to other risk factors such as ages at menarche and menopause. In this context, recent data from Dr. Willett's group suggest that weight gain in adulthood, as well as hormone use, may be a risk factor for breast cancer.

Researchers are now beginning to apply information gained from the descriptive studies to development of new therapeutics. For example, Jeffrey T. Holt, Vanderbilt University Cancer Center, Nashville, Tenn., is using a novel treatment for cancer patients who have germline BRCA 1 mutations. His group is currently testing the use of BRCA 1 retroviral therapy. Twelve women with advanced ovarian cancer have received peritoneal injections of retroviral vectors that express wild-type BRCA 1. Results of this study are eagerly awaited to learn whether the retroviral vector is taken up by the cells, whether the BRCA 1 protein is expressed, and, finally, whether its expression reduces tumor progression.

In summary, breast cancer continues to be a major life-threatening disease among women, and therefore poses a tremendous challenge to researchers and clinicians interested in improving the methods of prevention, diagnosis, and treatment. This conference provided ample evidence that important strides are being made to more fully understand the etiology of the disease and to begin applying the new knowledge in order to achieve these goals.

Mary S. Wolff is Professor of Community Medicine at Mount Sinai School of Medicine, New York City.

The drawing Aida and the Mirror (above) is by Selma Bortner, and is part of Confronting Cancer through Art, an art exhibit and "virtual gallery" of works by cancer survivors or artists responding to the illness of a family member or friend.

Endlinks

Lawrence Livermore National Laboratory is a major center for breast cancer research in the United States. The home page has listings for scientific programs, research news, publications, computing sciences, educational programs, library, and technology transfer material. The ELSI Project covers ethical, legal and social issues. See also Important New Findings Reported In Breast Cancer Study.

Oncolink: The University of Pennsylvania Cancer Center Resource includes menus for specific types of cancer, specific treatments, causes, psychosocial and personal support issues, cancer causes, lists of ongoing clinical trials, conferences and meetings, and financial issues for patient billing.

CenterWatch Clinical Trials Listing Service is an international listing of clinical research trials. This site has listings for clinical trials, information about physicians and medical centers performing clinical research, and drug therapies newly approved by the Food and Drug Administration. They also have an E-mail notification service to inform users of future postings in a particular therapeutic area.

Telomorase - the end of cancer? For the lay audience, an informative article on telomerase and cancer.

The purpose of the Program on Breast Cancer and Environmental Risk Factors in New York State is to provide scientifically based information on the relationship of environmental factors, including pesticides and diet, and the risk of breast cancer.