Abstract P2-10-33: Mitotic Component of Grade Can Distinguish Breast Cancer Patients at Greatest Risk of Local Relapse

Abstract

Abstract Background: With the recent recognition of many different molecular subtypes of breast cancer a desire to more specifically categorize tumors to allow tailoring of treatment to individual patients has developed. This has largely involved the development of molecular tests rather than the re-examination of current pathologic criteria. We wanted to evaluate standard pathologic features to determine their ability to predict for local recurrence. Materials and Methods: Slides were retrieved for review from 280 of 769 women who had participated in a trial of tamoxifen with or without breast irradiation between December 1992 and June 2000 and for whom outcome data up to 18 years was available. All women were 50 years of age or older at the time of enrollment and had T1 or T2 node negative breast cancer. The cases for which slides were obtained were representative of the whole group. The slides were reviewed by two breast pathologists (SJD and NAM). Several features were evaluated; modified Nottingham histologic grade and its components- degree of tubule formation, nuclear pleomorphism and mitotic count. Mitotic component of grade was calibrated to the microscopic field size used. The presence of lymphatic/vascular space invasion was also scored. A statistical analysis was performed to relate these pathologic features to local recurrence at up to 18 years. Results: The strongest predictor of local recurrence was the mitotic component of the Nottingham histologic grade with 5.7% for mitotic score 1/3 (n = 200), 19.6% for mitotic score 2/3 (n = 37) and 19.8% for mitotic score 3/3 (n = 43)(Gray's p-value = 0.0021). Overall grade was also able to predict for local recurrence with 2.6% for Grade 1 (n = 49), 10.6% for Grade 2 (n = 162) and 17.9% for Grade 3 (n = 71)(Gray's p-value=0.026). However, neither architecture (0% vs. 9.5% vs. 9.8%, Gray's p-value=0.74) nor degree of nuclear pleomorphism (0% vs. 7.9% vs. 11.5%, Gray's p-value=0.37), the other components of histologic grade, showed a statistically significant difference for recurrence. The presence or absence of endothelial lined space invasion was also found to be not statistically different (9.3% vs. 13%, Gray's p-value=0.55). Conclusion: Within this cohort of tamoxifen treated T1 and T2 breast cancer patients 50 years of age or older, mitotic index could stratify women into groups with high and low risk of recurrence. If validated this may be a useful way of allocating patients to different treatment groups. Additional validation studies are planned on similar groups of patients. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-10-33.