The pathology of breast cancer detected by mass population screening.

Breast cancer was detected in 156 of 17,526 asymptomatic women, (8.9/1000), aged 45-64 years, screened by mammography, thermography, and physical examination, Twenty-six percent of 149 pathologically reviewed cases metastasized to axillary nodes. Thirty-six percent of tumors were in situ, minimally invasive, or low grade tubular carcinomas, none of which metastasized. Increased rates of detection were shown for intraductal and tubular types. Frankly invasive ductal and lobular carcinomas had a mean diameter of 2.3 cm., 46% of which had axillary lymph node metastases. Seventy-percent of these were to only one to three nodes, however. Multicentricity with intraductal and lobular carcinoma in situ was frequently observed. Metastatic potential was related to tumor size, degree of stromal invasion, lymphatic permeation, and histologic grade. Few histological parameters other than size could be considered favorable. Forty-two percent of tumors were not palpable, the majority being in situ, minimally invasive, and tubular types. Only five nonpalpable invasive carcinomas metastasized. While the initial results of mass screening appear favorable, prolonged follow-up is needed to determine its impact on the population at risk.