Genetic Staging of Breast Cancers for Adjuvant Therapy. The overall objectives of this study are to elucidate the genetic processes that underlie the growth and clinical progression of human breast cancers, in order to provide a sound biological basis for the selection of patients with early clinical disease who are at high risk for recurrence, and who might benefit from adjuvant therapy. We will examine the interrelationship between HER-2/neu and H-ras amplification/overexpression, and the relationship between oncogene overexpression and flow cytometric aneuploidy. Our specific aims are: 1) to compare the sensitivity of detection of HER-2/neu and H-ras overexpression in early breast cancer by flow cytometry and by conventional molecular genetic techniques; 2) to determine if the number of genetic abnormalities, or their cellular distribution (multiple oncogenes expressed in the same cells or in different cells) are of biological and clinical importance, 3) to examine the degree of oncogene overexpression per cell in relation to tumor aggressiveness, and to determine if high levels of HER-2/neu and H-ras overexpression are due to, increased oncogene-bearing chromosome copy numbers per cell, and 4) to determine if oncogene overexpression occurs preferentially in aneuploid cells by means of multiparameter flow cytometry. The application of conventional molecular genetic techniques, multiparameter flow cytometry, and chromosome-specific probe studies to cells from the same tumors should provide a comprehensive view of the genetic evolutionary changes in breast cancer. A provisional staging system is proposed, .that is based on the degree of genetic evolution found in the primary tumor. The clinical validity of this staging system, and, in particular, its usefulness in identifying those patients with ostensibly early clinical disease who are most likely to benefit from adjuvant therapy will be assessed in relation to clinical tumor aggressiveness, as determined by long-term clinical followup studies.