Invasive lobular breast cancer. Prognostic significance of histological malignancy grading.

Invasive lobular carcinoma (ILC) is the second most reported type of breast cancer in the Danish Breast Cancer Cooperative Group (DBCG). Several histological subtypes exist, with reports of different prognosis. The aim was to present the incidence of ILC in DBCG from 1977-2004, and evaluate tumours regarding diagnosis, histological subtype and grade, and relate to prognosis. Eight hundred and sixty tumours from patients with a diagnosis of ILC or ILC/non-ILC, who underwent breast cancer surgery in the period of 1990-1998, were evaluated. The impact of histological malignancy grade on disease-free survival and overall survival was analysed using a multivariate analysis adjusting for tumour size, hormone receptor status, axillary lymph node status and patient age. The incidence of pure ILC has risen from 5 to 12%, the ILC/non-ILC is constant at 2% of all reported breast cancers in DBCG. Most of the tumours were classical ILC grade II. The majority of the grade III tumours were among the non-classical subtypes, showing a statistically significant worse disease-free and overall survival compared to grade II, regardless of type. The prognosis was the same for grade I and grade II tumours. The number of positive axillary lymph nodes and hormone receptor negative tumours increased among grade III tumours. We conclude that histological malignancy grade has an independent significant impact on the prognosis of ILC, and it should be taken into consideration when planning the postoperative treatment in this group of patients.