Interval breast cancers are not biologically distinct--just more difficult to diagnose

Breast cancer diagnosed within 1 year of a negative annual screening examination is called interval breast cancer (IBC) and is considered to be a more virulent subtype of disease.

We reviewed clinical data on 24 women who were diagnosed as having IBC while participating in the Breast Cancer Detection Demonstration Project at Ellis Fischel Cancer Hospital and the Women's Cancer Control Program screening project in Columbia, Missouri, between 1974 and 1992. We reinterpreted mammograms from the visit prior to the diagnosis of IBC for possible misdiagnosis, changes suggestive of malignancy, and Wolfe's patterns. Archival paraffin blocks from 19 patients were used to determine qualitative expression of tumor markers.

Observed 5-, 8-, and 10-year survival rates were identical to published data for patients with non-IBC. Seventy-four percent of the mammograms evidenced dysplastic Wolfe's patterns (P2 and DY), and one patient was found retrospectively to have shown evidence of cancer which was missed. Compared to breast cancers in general, fewer IBC tumors expressed tumor markers associated with poor prognosis.

Survival rates and tumor marker expressions in this retrospective cohort suggest that IBC tumors are not more biologically aggressive than noninterval tumors. They are more difficult to diagnose both by physical examination and mammography.