The diffuse type of invasive lobular carcinoma of the breast: morphology and prognosis

Invasive lobular carcinoma (ILC) of the breast represents a heterogeneous group of tumors, which can be classified according to the histological growth pattern into classic ILC and its variants and according to the cytomorphological characteristics into pleomorphic and non-pleomorphic subgroups. The most established morphological prognostic factors in ILC are the lymph-node status, the tumor size and the presence or absence of pleomorphic cytological features. In the present study, we analyzed the distribution of the lesions in 130 consecutive cases of ILC documented on large histological sections and followed up to, on average, 78 months (range 4-131 months). We found that 39% of the cases were unifocal, 12% multifocal, 28% diffuse and 19% combined (where the term combined represents those cases containing minor areas of diffuse growth of the tumor cells). In three cases, the distribution of the lesions could not be assessed. The diffuse cases were associated with a higher cancer-related death rate (25%) than the average (12%), the unifocal, the multifocal and the combined tumors (6-8%). The diffuse growth pattern represented a significant negative prognostic factor in relation to overall survival, but not in relation to disease-free survival. The only further negative prognostic factors found in this study were: more than three positive lymph nodes, tumor size larger than or equal to 40 mm and presence of pleomorphic cytological features. We propose to delineate the diffuse group of the ILCs as a separate diagnostic category with distinct morphological and radiological features and with unfavorable prognosis.