Prospective evaluation of periodic breast examination programs.

A mathematical model is developed to obtain prospective estimates of average tumor sizes and the expected proportion of positive regional lymph node cases for periodic breast cancer examination programs. Semiannual, annual, and biannual programs, with or without mammography, are evaluated and compared with results from the National Breast Poject. Calculations indicate that a semiannual clinical-mammographic program can be expected to result in about 37% fewer positive node cases than those observed in the National Breast Project and substantially small tumors. The expected reduction in positive node cases from a similar annual program is about 30%, and from a biannual program, even without mammography, about 20%. Calculations also indicate the important role of diligent patient self-examination in such programs, especially for the detection of fast-growing tumors.