Assessment of malignancy potential in so-called interval mammary carcinomas.

Forty-two so-called interval cancers of the breast were studied. The mammograms were reviewed and the tumors were classified as 14 'unrecognized', 9 'observer error', 1 'technical error' and 18 'true' interval cancers. By using a scoring system based upon histologic differentiation, axillary nodal status, estrogen receptor level, and nuclear DNA content, eight ductal carcinomas with high malignancy potential were identified. All of these tumors belonged to the group 'true' interval cancer. The data indicate that the mammographic subgroup 'true' interval cancer identifies the highly malignant tumors. However, even this strictly selected subgroup is heterogeneous since it also includes some tumors with low malignancy potential.