Invasive lobular carcinoma (ILC) comprises approximately 5-15% of breast cancers and appears to have a distinct biology. As it is less common than invasive ductal carcinoma, few studies of large size have addressed the value of assessment of histologic grade in ILC.
Methods: This study is based on a large and well-characterised consecutive series of breast cancer (4,987 cases), from a single institution, with a long-term follow-up to assess the prognostic value of routine assessment of histologic grade in ILC. Histologic grade and other clinicopathological data were available in 517 pure ILC cases. A panel of biomarkers was also available for 215 cases.
Results: The majority of ILC was of classical and mixed lobular variants (89%). Most ILC cases were moderately differentiated (grade 2) tumours (76%), while a small proportion of tumours were either grade 1 or 3 tumours (12% each). There were positive associations between histologic grade and other clinicopathological variables of poor prognosis such as larger size, positive lymph node, vascular invasion, oestrogen receptor and androgen receptor negativity and p53 positivity. Multivariate analyses showed that histologic grade is an independent predictor of shorter breast cancer specific survival and disease free interval.
Conclusion: Histologic grade of ILC, as assessed by the Nottingham grading system, provides a strong predictor of outcome in patients with invasive lobular carcinoma of the breast and should be provided routinely in pathology reports.