Epstein-Barr Virus in Breast Cancer Tissues

Institution: Cancer Prevention Institute of California
Investigator(s): Sally Glaser, Ph.D. -
Award Cycle: 2003 (Cycle IX) Grant #: 9WB-0005 Award: $275,260
Award Type: STEP Award
Research Priorities
Etiology and Prevention>Etiology: the role of environment and lifestyle

Initial Award Abstract (2003)
Nearly all persons are infected with Epstein-Barr virus (EBV) by adulthood and remain chronically infected for life. While almost all EBV infections are benign, a small percentage of infected persons develop certain cancers (lymphomas, stomach cancer, nasal cancer) with this virus present. Recent studies suggest a link between EBV and breast cancer. Understanding this link is potentially important and timely, as it would not only provide new knowledge about breast cancer but also help identify women at risk for this type of breast cancer, who might benefit from use of the virus as a tumor burden marker that could potentially assist in early diagnosis or in measurement of post-therapy residual disease. However, study findings about the EBV-breast cancer association have been variable, due in large part to technical laboratory difficulties in determining if EBV in breast tumors is in the breast cancer cells themselves, which would suggest that the virus impacts tumor development. New laboratory technologies are available that could be used to overcome the previous technical limitations in this research, but these tests need to be developed to reliably detect EBV in stored breast cancer tissues.

Although scientific evidence is mixed, breast cancer is now hypothesized to be related to EBV in some patients. However, the virus may be difficult to detect in breast tumors because it is defective or partially deleted or may be present in only a minority of tumor cells. Development of new sensitive laboratory tests can help us overcome these problems and study the EBV-breast cancer link so as to accurately determine the proportion of women with EBV in their tumors and begin to describe their characteristics with regard to age at diagnosis, race, socioeconomic status, extent of disease spread, and survival.

We will first identify a group of 100 Greater Bay Area women with breast cancer who are representative of all patients with this disease. With their permission, we will obtain very small samples of their tumor tissue left over from their diagnosis, and we will test these for EBV using new, state-of-the-art laboratory procedures that we will develop as part of this study. One of these tests, called “real-time PCR”, is so powerful that it lets us find "a needle in a haystack”, and then count how many “needles” are present. (PCR or polymerase chain reaction is a technique for rapidly producing many copies of a fragment of DNA.) This laboratory test will allow us to determine how much EBV is present in each breast cancer tissue sample. Another new method, called ”laser capture microdissection”, will allow us to further determine if EBV we detect is in the cancer cells or merely in the surrounding normal cells. Once we have developed the tests to reliably determine if a breast cancer contains EBV, we will be able to begin identifying the characteristics of women (i.e., age, race/ethnicity, socioeconomic status, extent of disease spread, prognosis) who have this type of breast cancer.

Investigating the possible link between EBV and breast cancer is important because it will help us better understand why this important cancer of women develops, and it may provide new tools that can be used for early diagnosis, treatment and prevention. The study is innovative in combining the best laboratory methods now available to look for EBV in breast tumor cells, and in studying a representative group of women to maximize the chances of identifying those at risk for EBV-related breast cancer. If EBV is found to be present in cancer cells of even a small percentage of patients, these women may be candidates for new therapies that target infected cells.

Final Report (2006)
Some studies have reported a link between breast cancer and EBV (Epstein-Barr virus), a common virus that infects almost everyone by adulthood. However, findings have varied across these studies, due in part to technical laboratory difficulties in measuring EBV in breast tumors. For most other EBV-related cancers, EBV is only found in tumors of patient subgroups defined by specific demographic and clinical characteristics, yet this possibility has not been much considered for breast cancer.

To address these limitations, we developed a battery of laboratory tests to detect EBV and applied them to stored breast cancer tissues from women at higher and lower risk of breast cancer, defined by race/ethnicity and age, and with less and more aggressive disease. We completed all study aims. We refined our definition of non-white study subjects to include only Latinas, who are at low risk of breast cancer. We were not able to obtain all tumor specimens we sought, due to variability in hospital cooperation with our requests. Because of the very small amount of EBV detected, we used a different strategy than initially planned to locate specific infected cells. We developed three new molecular tests for detecting EBV and checked carefully to see that they worked reliably. Applying the tests to tumor tissues from non-Hispanic white and Latina breast cancer patients, we found very low levels of EBV in tumors of about one in five patients in both racial/ethnic groups. These low levels, which are similar to findings from other recent studies, indicate that EBV is very unlikely to have caused the tumors to develop.

However, we found some differences in demographic and clinical characteristics between women who did and who did not have EBV in their tumors: tumors with EBV tended to occur in women with more advanced and aggressive disease at diagnosis. For women over age 50 at diagnosis, those with virus found in their tumors were more likely to have had a previous cancer, which might reflect increased susceptibility to viral reactivation due to immune suppression from prior cancer treatments; for those also with advanced disease at diagnosis, EBV-related tumors were more likely to be in the left breast, which may be related to the larger size and thus greater amount of tissue in the left breast. Latina women were more likely than non-Hispanic white women to have higher levels of virus detected. There was no effect of EBV on survival after >20 years of follow-up.

Overall, our findings, like reports from other studies, suggest that EBV may play some role in increasing breast cancer aggressiveness. Because EBV appears to be relevant to a proportion of breast cancers and in ways with relevance to treatment decisions, the findings of this preliminary study should be evaluated in a larger study that can look in more detail at EBV-related breast tumors.

Variation in risk and outcomes of Epstein–Barr virus-associated breast cancer by epidemiologic characteristics and virus detection strategies: an exploratory study