Interval breast cancers more likely to be aggressive

Interval breast cancers-those found within 24 months after a negative screening mammogram or identified retrospectively on a mammogram-are more likely to have high-risk characteristics linked to aggressive behavior and poor prognosis than cancers detected at the time of a screening mammogram, according to a Canadian study. These features include higher stage and grade, larger size, and lack of estrogen and progesterone receptors.

Researchers compared tumor characteristics in women 50 years of age and older screened in the Ontario (Canada) Breast Screening Program between 1994 and 2002. Eighty-seven women had interval cancers overlooked on mammography, 288 women had true interval cancers (ie, not detectable on mammography), and 450 women had cancers that were found on mammography.

True interval cancers were almost 4 times as likely as screen-detected cancers to be larger than 2 cm in diameter, more than 4 times as likely to be stage III or IV as stage I, more than 3 times as likely to be poorly differentiated, approximately 3 times as likely to be growing quickly, and about twice as likely to be estrogen receptor-negative and progesterone receptor-negative. Missed interval cancers also were more likely than screen-detected cancers to be large and poorly differentiated and to have invaded the lymph nodes.

“The findings suggest a need for more sensitive screening modalities to detect true interval breast cancers and different approaches for early detection of fast-growing tumors,” the authors write.

Both true and missed interval cancers were higher stage and grade than screen-detected tumors; however, true interval cancers were more likely to have additional characteristics suggesting an adverse prognosis, such as estrogen and progesterone receptor negativity.

The study was published online May 3 in the Journal of the National Cancer Institute.