The natural history of breast carcinoma - What have we learned from screening?

BACKGROUND; The availability of breast carcinoma data from trials of mammog raphic screening provides an opportunity to study the natural history of br east carcinoma. METHODS. The Swedish Two-County study is a randomized, controlled trial of mammographic screening for breast carcinoma in which 77,080 women were rand omized to receive an invitation to mammographic screening and 55,985 were r andomized to receive no invitation. During the trial, a total of 2468 breas t carcinoma cases were diagnosed. The authors examined the effect of screen ing on the pathologic attributes of the tumors diagnosed, mortality and sur vival from breast carcinoma, and the consequences of arresting tumor develo pment by screening. RESULTS. Screening reduces mortality from breast carcinoma largely through its effect in detecting tumors at a smaller size, decreasing the probabilit y of lymph node metastases, and reducing the opportunity for worsening of t he grade of malignancy of the tumor. CONCLUSIONS. Breast carcinoma is not a systemic disease at its inception, b ut is a progressive disease and its development can be arrested by screenin g. The point at which the tumor's progression is arrested is crucial. Detec tion of small (<15 mm) and lymph node negative invasive tumors will save li ves and confer an opportunity for less radical treatment. Tumor progression in the preclinical phase occurs more rapidly in women age <50 years, sugge sting the need for a shorter screening interval for this group. (C) 1999 Am erican Cancer Society.