Detection of breast cancer on screening mammography allows patients to be treated with less-toxic therapy

OBJECTIVE. Therapy for breast cancer is accompanied by acute and chronic toxicity. Little research has been conducted to determine the impact of the mode of breast cancer detection on the likelihood of receiving different types of treatment. The objective of this study was to determine whether detection of breast cancer on screening mammography is associated with less-toxic therapy. MATERIALS AND METHODS. The study group for this retrospective cohort study consisted of 992 women with invasive breast cancer detected on screening mammography (n = 460) or at physical examination (n = 532) at a single institution between 1990 and 2001. To address the generalizability of study findings, we compared the characteristics of study participants with those diagnosed with breast cancer in a population-based mammography registry. RESULTS. The patients whose breast cancer was detected on screening mammography more frequently had lymph nodes free of metastases (84% vs 58%, p < 0.0001), had smaller tumors (1.5 vs 2.9 cm, p < 0.0001), were more likely to be treated with breast conservation (56% vs 32%, p < 0.0001), and were less likely to be treated with chemotherapy (28% vs 56%, p < 0.0001). In a multivariate analysis with adjustments for age and functional status, patients whose cancer was detected at physical examination were more than twice as likely to undergo mastectomy (odds ratio [OR], 2.5; 95% confidence interval [CI], 1.9-3.3) and nearly three times as likely to be treated with chemotherapy (OR, 2.9; 95% CI 2.1-3.9). For younger women (40-49 years old), the likelihood of receiving chemotherapy was more than doubled if the cancer was detected at physical examination rather than on screening mammograms (OR, 2.3; 95% CI 1.3-4.0). For older women (greater than or equal to 70 years old), patients whose cancer was detected at physical examination were five times more likely to undergo mastectomy (OR, 5.8; 95% CI, 3.2-10.5) and four times more likely to receive chemotherapy (OR, 4.6; 95% CI, 1.6-13) than the group whose tumors were detected on screening mammography. CONCLUSION. Breast cancers detected on screening mammography are smaller, are less likely to metastasize to lymph nodes, and are more likely to be treated with breast conservation and without chemotherapy. These findings provide an additional rationale for performing screening mammography, especially for women at age extremes for whom the survival benefit of screening mammography is debated.