Omission of histologic grading from clinical decision making may result inoveruse of adjuvant therapies in breast cancer: Results from a nationwide study

Purpose: To investigate the influence of routinely performed histologic gra ding on breast cancer outcome prediction and patient selection for adjuvant therapy. Patients and Methods: The analysis is based on a cohort of 2,842 women diag nosed with breast cancer and comprising 91% of all breast cancers diagnosed in five defined geographical regions in Finland in 1991 through 1992. Data on clinicopathologic factors and follow-up were collected from hospital ca se records and national registries. Histologic grade assessed at diagnosis and other clinicopathologic data were available for 1,554 operable unilater al invasive carcinomas. The relative value of grade with respect to competi ng prognostic factors was estimated with the Cox proportional hazards model and logistic regression. Interactions and nonlinearity of factors were acc ounted for by using an artificial neural network. Results: Histologic grade was correlated strongly with survival in the enti re series and in all subgroups studied. Women with well-differentiated node -negative cancer had a 97% 5-year distant disease-free survival rate as com pared with 78% for women with poorly differentiated cancer. Grade was an in dependent prognostic factor in multivariate models and increased the predic tive accuracy of a neural network model. Inclusion of grade data in a Cox m ultivariate model based on tumor size and hormone receptor status in node-n egative cancer increased the proportion of patients with 5% or less risk fo r distant recurrence at 5 years from 15% to 54%. Conclusion: Even when assessed by pathologists who have no special training in breast cancer pathology, histologic grade has substantial and independe nt prognostic value in breast cancer. Omission of grading from clinical dec ision making may result in considerable overuse of adjuvant therapies. J Cl in Oncol 19:28-36. (C) 2001 by American Society of Clinical Oncology.