Regional differences in breast cancer survival are correlated with differences in differentiation and rate of proliferation

Abstract

Patients with invasive ductal breast cancer and with 5 to 12 years of follow-up, identified from two pathology laboratories serving hospitals in two distinct but fairly close regions, were studied for differences in length of survival. In the years when the cases were diagnosed, population screening was not performed, adjuvant systemic therapy was not administered, and surgical treatment and irradiation protocols were similar in the hospitals served by the two laboratories. There was a significant difference in length of survival between the two regional groups (N1 = 160, N2 = 111; P = .006). Survival rate at 10 years in the two regions was 48% and 69%. Distribution of age, tumor size, and lymph node status (as negative or positive as well as number of positive nodes) were similar, but quantitative and qualitative microscopic features differed. Patients from the region in which the prognosis was less favorable had the higher median values for the mitotic activity index (14 v 4; P < .0001) and for nuclear area (59.2 v 38.2; P < .0001). Nuclear and histologic grade distributions were also different between the regions. Logistic regression analysis confirmed that the regional survival differences are correlated with the microscopic features, even after adjustment for age, tumor size, and lymph node status. Comparison of breast cancers from the periods 1970 to 1974 and 1988 to 1989 in one of the two regions revealed that the clinical and microscopic proliferation features were similar over time. These results, apart from indicating regional variation in breast cancer survival rate correlated to differences in the microscopic characteristics of the disease between regions, provide additional support to previous reports that qualitative and, especially, quantitative microscopic differentiation and proliferation features have significant bearing on the prognosis of breast cancer patients.