A mathematical model is developed to obtain prospective estimates of average tumor sizes a n d the expected proportion of positive regional lymph node cases for periodic breast cancer examination programs. Semiannual, annual, and biannual programs, with or without mammography, a r e evaluated and compared with results from the National Breast Project. Calculations indicate that a semiannual clinical-mammographic program can be expected to result in about 37% fewer positive node cases than those observed i n the National Breast Project and substantially smaller 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%. Calcnlations also indicate the important role of diligent patient self-examination i n such programs, especially for the detection of fast-growing tumors.Cancer 38:265-272, 1976.
NNUAL EXAMINATION PROGRAMS FOR EARLYA breast cancer detection have been reported to yield favorable survival statistics at the Cancer Detection Center of the University of Minnesota7 and the Health Insurance Plan of Greater New York.17tZ0 Semiannual examination schedules have been suggested for earlier cancer detection in the hope that they may result in more favorable survival statistics.4 However, except tor tlie mammography program conducted by G~rshon-Cohen,~ the semiannual examination idea does not seem to have been evaluated experimentally.I n previous papers,lO,ll we developed a mathematical model that could be used to characterize any examination schedule in terms of the expected delay between the first point at which a tumor could be detected, if an examination happened to be performed at that time, and the point at which it is actually found. T h e purpose of this paper is to extend that model by using the length of the expected detection delay associated with a given periodic examination program to estimate a) tlie average tumor size of those women in the program who get breast cancer, 11) the proportion of those patients with axillary node metastases, and c) the expected "lead time" gained by early cancer detection in program patients over those reported on in the National Breast Project. T h e methodology can be used to obtain estimates of these factors for any given examination schedule. We shall use it to obtain such estimates for seniiannual, annual, and biannual programs, itssuming both physical and mammograpliic examination motlali ties.
