Does routine grading of invasive lobular cancer of the breast have the same prognostic significance as for ductal cancers?

Aim: The routine tumour grading of invasive ductal carcinoma of the breast has been shown to be a robust determinant of outcome but pathologists have been reluctant to grade lobular cancers. The aim of this study was to determine the prognostic significance of the routine reporting of lobular grade. Methods: All patients with invasive lobular carcinoma (ILC) treated between 1981 and 1996 were reviewed. Patients with ILC which had been graded were included in the study. These cases were matched with two control patients with invasive ductal carcinoma (IDC) who were operated on in the same year and were closest to the patients in age. Recurrence-free survival was compared with grade for ILC cases and IDC controls using life-table analysis. Similar comparisons were made with the Nottingham Prognostic Index (NPI) between the different prognostic groups. Results: Of 139 cases with ILC, 33 were excluded from the study because 24 were ungraded, five had advanced disease and four had mixed tumours. The mean length of follow-up for ILC cases was 75 months vs 70 months for IDC controls. Recurrence rates for grade I were 10% ILC vs 24% IDC, for grade II 32% vs 32% and for grade III 33% vs 49%. The reported grades for ILC and IDC both showed the expected trend for an increased recurrence rate with more severe tumour grade, but this was only significant for IDC grade II vs grade III (P<0.02) on life-table analysis; only 6% of lobular cancers were reported as grade III. However, there was significant separation of the survival curves when NPI was compared for both lobular and ductal cancers. Conclusion: The routine reporting of tumour grade for ILC did not show significant difference in outcome between grade I and grade II, and very few tumours were rated grade III. The validity of grading lobular cancer of the breast requires further evaluation.