While research has shown that younger women with breast cancer face an increased risk of dying from their disease if they have recently given birth, the characteristics of their tumors have not, until now, been thoroughly studied.
For the first time, researchers from the Fred Hutchinson Cancer Research Center appear to have found biological evidence to support the observation that younger women diagnosed with breast cancer within two years of childbirth are at twice the risk of dying from the disease as compared to women with less recent or no history of childbirth.
Writing in the journal Cancer Epidemiology, Biomarkers and Prevention, Janet R. Daling, Ph.D. and colleagues reported on their analysis of the medical records and breast-tumor samples from 1,174 women age 45 and younger who were diagnosed with invasive ductal breast cancer (the most common form) between 1983 and 1992. The women were followed for an average of nearly nine years. At the end of follow-up, 48 percent of those whose last birth occurred within two years of diagnosis had died, compared to 23 percent of the women who had never given birth and 24 percent of the women whose last birth was at least five years before diagnosis.
"We looked at a broad panel of tumor markers associated with poor prognosis and found that the histologic grade, or evidence of aggressiveness, was almost six times higher in the tumors of these women," said Daling. She said their findings narrow the search for tumor markers linked to poor survival in younger women who've recently given birth, and they provide new clues about the mechanisms involved in their cancer development and progression.
Such markers potentially could be used to determine the aggressiveness of treatment for such women. Understanding these mechanisms also could lead to the development of new drugs to prevent and treat breast cancer.
Why were women who had recently given birth prior to breast-cancer diagnosis at more than twice the risk of dying from their disease? The researchers suspect it has to do with hormones, although no one knows for sure.
"The hormones of pregnancy are most likely causing pre-existing abnormal breast cells or tumors to grow very quickly and become very aggressive in these women," Daling speculated.
In an effort to understand the biology behind this aggressiveness, breast-tumor samples were obtained from 70 percent of these women. If tumor samples were unavailable, original pathology reports were used.
The tumors of the women who had most recently given birth exhibited a distinct variety of characteristics associated with active cell division-markers of rapid cancer growth. Markers evaluated and found to be implicated in the aggressiveness of their cancer included:
Estrogen- and progesterone-receptor status (positive or negative) - a marker that has been tested and used to assess the likelihood of outcome regarding mortality or cancer recurrence. Loss of estrogen and progesterone receptors on tumor cells (i.e., ER- or PR-negative status) is associated with poor clinical outcome and lack of response to anti-hormonal therapies such as tamoxifen.
Mitosis - active cell division as determined by looking at the cancer cells under a microscope. Tumors with a high mitotic count are more aggressive.
S-phase - the "synthesis phase" of the cell cycle in which the DNA duplicates, a characteristic of active cell division.
P53 - a protein product made by the p53 tumor-suppressor gene. When detected in large amounts, it often is associated with abnormal function of p53 and loss of cell-cycle control, which can lead to cancer. The women with a recent history of childbirth were two and-a-half times more likely to have "p53-positive" tumors.
Ki-67 - another marker of active cell division. A high percentage of tumor cells positive for the Ki-67 protein is an indicator of rapid tumor growth.
c-erB-2 - an oncogene (also known as HER-2/neu) which, when amplified, is associated with poor prognosis. This gene, currently an attractive cancer-vaccine target, is abnormally expressed in 20 percent to 30 percent of breast cancers.
The researchers also evaluated tumor size, lymph-node involvement and cancer stage (how far the cancer had metastasized, or spread).
All of these markers currently are being used clinically, particularly at academic medical centers, said co-author Dr. Peggy Porter, and potentially they could be used in breast-cancer patients with a recent childbirth history to help determine the aggressiveness of treatment.
"One wouldn't want to treat these women aggressively based on the sole fact that they had a recent pregnancy," she cautioned. "But one would want to test their tumors with this panel of screening tools and treat them based on the aggressiveness of the tumor."
SOURCES:
Cancer Epidemiology, Biomarkers and Prevention, March 2002; 11:235-241
Fred Hutchinson Cancer Research Center (http://www.fhcrc.org)
