Approximately 30% of breast cancers are not detected at screening, but rather between two screening examinations, and are known as interval breast cancers.
Interval, breast cancers are likely to be diagnosed at later stages and are more likely to present with metastases in local lymph nodes, than patients with a diagnosis of mammographic screening detected cancers.
Interval breast cancers are more likely to be estrogen receptor negative, progesterone receptor negative, and triple negative as compared with screen detected breast cancers.
Interval, breast cancers are associated with a worse prognosis.
Patients with interval breast cancers, have a higher likelihood of having first-degree relatives with breast cancer.
Patients with interval breast cancers are also more likely than those with screened detected breast cancer to develop other tumors come indicating a genetic cause.
Higher mammographic density reduces screening sensitivities and increases the likelihood of subsequent interval breast cancer.
Factors contributing to interval cancers include: technical factors such as imaging technology and radiology interpretation, and patient specific factors, such as breast density.
Breast density reflects the relative amount of stroma and epithelial cells in contrast to fat, and dense breast areas appear white on the mammogram, the same as the tumor, making differentiation difficult.
Women with the family history of breast cancer are 1.3 times more likely to receive a diagnosis than women with screen detected cancer.
In a population based study of 527,144 women interval breast cancers were associated with in family history of breast cancer, hereditary breast and ovarian cancers, colorectal, and testicular cancers, as well as having dense breasts, hormone replacement therapy, older age at first childbirth, and higher educational level (Zhang Y).
The germline protein truncating breast cancer variants in five genes – ATM, BRCA1, BRCA2, CHEK2, and PALB2 all are strongly associated with the risk of breast cancer, and are found to be more common in patients with interval, breast cancers.