Other studies have shown that cancers diagnosed between mammograms, known as interval cancers, tend to have a worse prognosis than those detected during routine screening. This study examined the difference between "true" interval cancers—those not detectable on the previous mammogram—and "missed" interval cancers—those not detected on the previous mammogram due to technical errors or misinterpretation.
The authors, Anna M. Chiarelli, Ph.D., of Cancer Care Ontario, and colleagues, analyzed data from the Ontario Breast Screening Program for 288 women with true interval cancers and 87 women with missed interval cancers. Both kinds of interval tumors were compared to screen-detected tumors in 450 women who were similar in terms of age, location of the screening center, and length of time since their last mammogram. Their research was supported by a grant from the Canadian Breast Cancer Research Alliance.
As expected, the true and missed interval cancers were of higher stage and grade than screen-detected cancers. However, true interval cancers were also more likely to be estrogen receptor-negative and progesterone receptor-negative; to have a high mitotic index (a measure of how rapidly the tumor cells were dividing); and to have a less common histology (type of cancer and arrangement of cells).
The authors conclude that the findings suggest "a need for further advancement in imaging technologies to detect certain types of breast carcinomas and different approaches for early detection of fast-growing tumors."