MANCHESTER, ENGLAND – Older women who are breast cancer survivors have a greater risk of developing additional primary cancers in the long term than those under 65 years of age, according to an analysis of data on more than 100,000 survivors in the United States.
Women aged 70-79 years appear to have the highest risk of developing a multiple primary malignancy (MPM), with a crude 10-year incidence of 17.8/10,000 person-years. In comparisons, the rate of risk for survivors younger than 65 was 11.7, increasing to 16.7 for those 65-69 years of age and 16.4 for those 80 years and older.
Other common cancers occurring in the breast cancer survivor population were lung and colon cancers, investigator Kerri Clough-Gorr, D.Sc., reported at the annual meeting of the International Society of Geriatric Oncology. Hematologic malignancies, melanoma, and urinary and digestive tumors were also observed.
"Relative breast cancer survival rates are quite high in the United States, at over 89% at 5 years [after a diagnosis]," said Dr. Clough-Gorr of Boston University and the Institute of Social and Preventative Medicine at the University of Bern (Switzerland).
"Importantly, the vast majority of women with breast cancer become long-term survivors, and they are at risk for developing subsequent malignancies," she added.
It is estimated that there are 2.4 million women in the United States with a history of breast cancer, and the current study aimed to look at survivors’ risk of developing multiple primary cancers over a 20-year follow-up period.
The study analyzed data from 12 SEER (Surveillance, Epidemiology, and End Results) program registry sites on 110,440 women diagnosed with a first primary breast cancer between 1986 and 1994. The women were evaluated for the development of other primary cancers or death up until 2006.
In addition to being more likely to develop another primary cancer, older women were more likely to develop it more quickly. The mean time to develop any MPM was 50 months for women 80-plus years compared with 100 months in those under 65 years. Values for women aged 65-69 and 70-79 were 85 and 72 months.
The stage of the first primary breast cancer at diagnosis did not affect the risk of subsequent MPM, nor were any sociodemographic factors or the year of diagnosis found to be of influence.
"Age was the strongest, significant predictor of multiple primary malignancy risk in this population," Dr. Clough-Gorr noted, adding that the risk was highest in women 70-79 years, with a hazard ratio of 1.48. Hazard ratios for ages 65-69 and 80-plus years were 1.41 and 1.32.
"These findings suggest there are age-related differences in [the] risk of developing an MPM after a primary breast cancer diagnosis," Ms. Clough-Gorr concluded. "In this population, there were no other MPM risk factors that were identified."
The study was supported by the National Cancer Institute. Dr. Clough-Gorr said she had no relevant financial disclosures.