Risk of Second Malignancy Increases With Time

BOSTON—In a study of 1,253 breast cancer patients treated with breast-conserving surgery and radiotherapy, the risk of a second malignancy jumped from 5% at 5 years of follow-up to 16% at 10 years. Barbara L. Fowble, MD, of Fox Chase Cancer Center, reported the results at the 42^nd Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO).

The median interval to a second cancer was 6.1 years. For the 93 women who developed second breast cancers, the median interval was 5.8 years (range, 0.3 to 15.2). For the 98 with second cancers at other sites, it was 7.2 years (range, 0.3 to 18.4). Dr. Fowble urged long-term follow-up of these women to enable early detection of second malignancies both in the breast and at other sites.

Factors associated with increased risk of second malignancy included patient age and other patient characteristics, Dr. Fowble said. No treatment-related risk factors were identified. "The majority of patients will not develop a second cancer. However, certain subgroups are at risk," she said. "Knowledge of the risk and the patterns will influence surveillance and prevention strategies."

Younger women, especially those with a family history of breast cancer, were more likely to have a second breast cancer, and their risk increased with the number of relatives affected. With three or more affected relatives, the risk was 37%. While this is similar to the risk reported for breast cancer gene mutation carriers, Dr. Fowble warned that family history should not be considered a surrogate for determining gene mutation status.

Slightly more than half of the second malignancies were in sites other than the breast, and older age was a risk factor for these cancers, as was menopausal status. Family history of breast cancer was not associated with these cancers.

The total number of women with second cancers was 182, including 9 who had both breast and non-breast cancers. The most common non-breast malignancies were skin cancers (29 patients), gynecologic cancers (19 patients), and gastrointestinal cancers (18 patients). Eight patients developed lung cancer, and three developed leukemia.

All were treated for unilateral stage I-II breast cancer at the University of Pennsylvania or Fox Chase Cancer Center from 1978 to 1994. The majority (68%) were T1, and 73% were node negative.