ARCHITECTURAL PATTERN OF THE NORMAL AND CANCEROUS BREAST UNDER THE INFLUENCE OF PARITY

Epidemiological and clinical observations indicate that breast cancer incidence is greater in nulliparous women, whereas early parity confers protection. Since the initiation of breast cancer is related to the degree of development of the organ, this study was designed with the purpose of determining what basic differences exist between the parous and the nulliparous women's breast, and whether these differences correlated with the presence or absence of malignancies. For this purpose, the architecture of the mammary gland of parous and nulliparous women with breast cancer was compared with that of women free of mammary pathology. The women ranged in an age from 20 to 63 years. Normal whole breasts obtained at autopsy or cancer-bearing breasts surgically removed by modified radical mastectomy were studied in whole mount preparations in which the number and relative proportion of normal structures, i.e., lobules type 1, 2, and 3 (Lob 1, 2, and 3), were determined. In the breast of nulliparous women, the predominant structure present was the Lob 1; the presence of cancer did not modify the basic architectural pattern of the breast, which contained a higher proportion of Lob 1 as well. In parous women free of cancer, the breast contained a greater percentage of Lob 3 and a moderately increased number of Lob 2, with a concomitant reduction in Lob 1. Parous women with breast cancer, on the other hand, exhibited a different architecture in the mammary gland, which had a greater percentage of Lob 1 and a lower of Lob 3 than the noncancerous group, approaching the percentages found in nulliparous women. The overall number of structures was lower in the nulliparous and parous women with cancer than in their corresponding controls. The analysis of breast architecture according to the four different quadrants of the breast revealed that Lob 1 in nulliparous and Lob 2 and 3 in parous women with or without breast cancer were present in similar proportions in all the quadrants. It was concluded that no significant differences in architecture existed between the cancerous and noncancerous nulliparous breasts, whereas the breast of parous women with cancer was less developed and similar to the breast of nulliparous women, an observation that suggests that pregnancy in these women did not succeed in inducing the same degree of differentiation achieved by the breast of parous women free of malignancies. Determination of whether these differences in breast development are causally related to the initiation of cancer requires further investigation.