Factors Increasing Risk of Death from Breast Cancer Identified  


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Several studies presented at the Annual Meeting of the American Association for Cancer Research in Washington, DC, focused on factors associated with breast cancer mortality. One study found that older women with longer intervals between mammograms had a higher likelihood of dying of breast cancer. A second study had a somewhat surprising finding—that the BRCA1 mutation, but not BRCA2, was associated with a worse prognosis. A third study found that black women had the poorest prognosis regardless of breast cancer subtype.

Older Women and Mammogram Interval

An analysis of data from 9,929 women diagnosed with breast cancer in the Women’s Health Initiative during a 12.2-year follow-up found a significant association between mammogram interval and breast cancer mortality, especially in elderly women.1

“We found that for all women with breast cancer, including those aged 75 and older, a longer interval between the last mammogram and the date of breast cancer diagnosis was associated with a greater chance of dying of breast cancer,” said lead author Michael S. Simon, MD, MPH, Barbara Ann Karmanos Breast Cancer Institute in Detroit.

An interval of 5 years or more between the last mammogram and diagnosis of breast cancer was associated with advanced disease in 23%, compared with 20% of women with a shorter interval of 6 months to 1 year (P < .05). This difference is statistically significant and could affect large numbers of women, Dr. Simon said.

In an adjusted analysis, women with an interval of 5 years or more between mammogram and diagnosis or who never had a mammogram had a 1.7 times greater risk of breast cancer death compared with women who had an interval of 6 months to 1 year between mammogram and diagnosis (P for trend = .0008). Women aged 75 or older at diagnosis with an interval of 5 years or more between mammogram and diagnosis or who never had a mammogram had a three times greater risk of breast cancer death compared with women who had the shorter interval (P for trend = .0001). This relationship was not seen among younger women.

According to Dr. Simon, these findings suggest that regular mammography should be continued for older women every 1 or 2 years.

BRCA1 vs BRCA2 Mutations

A large retrospective study of 5,518 women diagnosed with breast cancer before age 50 at any of 10 clinics in the Netherlands between 1970 and 2002 found a 1.5 times greater risk of 5-year recurrence in women who carried the BRCA1 mutation (2.6% of the population) compared with noncarriers and a 1.2 times greater risk of 15-year death compared with noncarriers.2

“These data are from one of the largest, least-biased BRCA1- and BRCA2-genotyped breast cancer cohorts,” said lead author Marjanka M. K. Schmidt, PhD, Netherlands Cancer Institute in Amsterdam.

The proportion of estrogen receptor–positive tumors was similar between patients who were noncarriers and those with a BRCA2 mutation (86% and 81%, respectively), but only 29% of patients with a BRCA1 mutation had estrogen receptor–positive tumors.

A more refined analysis of the data is now underway—to look at other tumor characteristics, including tumor grade, tumor type, and immunhistochemical markers— with the goal of developing a predictive model, Dr. Schmidt said.

Black Women with Breast Cancer

When data were stratified by subtype and adjusted for breast cancer stage and treatment, black women appeared to have worse survival across cancer subtypes compared with other racial and ethnic groups in a prospective cohort of 1,688 breast cancer survivors enrolled in the Life After Cancer Epidemiology and Pathways study.3

“These data suggest that the difference in survival between black women and other racial/ethnic groups cannot be explained entirely by variable subtype diagnosis,” stated lead author
Candyce Kroenke, MPH, ScD, Kaiser Permanente Division of Research in Oakland, California.

At 6.3 years of follow-up, 499 deaths were reported. Of these, 268 were due to breast cancer. Black women were almost twice as likely to experience breast cancer–related death compared with white women. Black women were less likely to be diagnosed with either luminal A or luminal B subtypes than white women, but were more likely to be diagnosed triple-negative breast cancer, which is the most difficult-to-treat subtype, while luminal A is considered to have the best prognosis, she said.

Study findings included the following:

  • Black women with any subtype were more likely to die of breast cancer than white women diagnosed with the same subtype.
  • Black women with luminal A breast cancer were 2.3 times more likely to die than white women.
  • Black women with luminal B subtype were 2.6 times more likely to die than white women.
  • Black women with basal-like subtype were 1.3 times more likely to die than white women.
  • Among women with HER2-positive breast cancer, black women were 2.4 times more likely to die than white women.

Dr. Kroenke said that other studies have shown that black women are more likely to die of breast cancer than white women, but the reasons for the mortality gap remain a mystery, since the excess mortality is seen across different subtypes of breast cancer. More research is needed to explore this issue, she said. ■

Disclosure: Drs. Simon, Schmidt, and Kroenke reported no potential conflicts of interest.

References

1. Simon MS, Wasserstein-Smoller S, Thompson CA, et al: Mammography interval and breast cancer mortality in the Women’s Health Initiative. AACR Annual Meeting. Abstract 157. Presented April 7, 2013.

2. Schmidt MMK, van den Broek A, Tollenaar RAM, et al: Breast cancer survival of BRCA1/2 carriers compared to non-BRCA1/2 carriers in a large breast cancer cohort. AACR Annual Meeting. Abstract 1338. Presented April 8, 2013.

3. Kroenke C, Kwan M, Bernard P, et al: Race and breast cancer prognosis by PAM50 subtype in the LACE and Pathways studies. AACR Annual Meeting. Abstract 131. Presented April 7, 2013.



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