Background and methods: We examined the effect of adjuvant systemic therapy on survival after breast cancer among the residents of the Canadian province of British Columbia. Data on survival were collected for all women in whom breast cancer was diagnosed in British Columbia during each of three calendar years chosen to represent different province-wide treatment recommendations: 1974, when no adjuvant systemic therapy was recommended; 1980, when adjuvant chemotherapy was recommended only for premenopausal women with node-positive disease; and 1984, when adjuvant chemotherapy was also recommended for premenopausal women with node-negative disease and lymphatic, vascular, or neural invasion and tamoxifen was recommended for postmenopausal women with involved lymph nodes or lymphatic, vascular, or neural invasion unless their tumors were negative for estrogen receptors.
Results: For women less than 50 years of age, disease-specific survival at seven years (i.e., with censoring of data on women who died from causes other than breast cancer) improved from 65.2 to 76.3 percent between 1974 and 1984 (P = 0.008), and overall survival improved from 64.8 to 74.6 percent (P = 0.02). For women from 50 through 89 years of age, disease-specific survival at seven years improved from 62.5 to 70.4 percent between 1980 and 1984 (P = 0.001), and overall survival improved from 53.9 to 58.3 percent (P = 0.05). The timing of the improvements in survival correlated with the introduction of adjuvant systemic therapy in each group.
Conclusions: Survival among women with breast cancer improved significantly in a geographically defined population during the period when adjuvant systemic therapy became widely used.