Invasive Lobular Carcinoma

Invasive lobular carcinoma (ILC) is the second most common invasive breast carcinoma (IBC), comprising approximately 10 % of all IBC. Classical ILC is more likely to be clinically and mammographically occult than IDC and therefore, may present at a later stage. Classical ILC is hormone receptor (HR) positive and HER2 negative. As in IDC, histologic grading of ILC should be performed. High grade ILC is uncommon and may be HR negative and HER2 positive. E-cadherin can aid in diagnosing ILC; however, aberrant staining can occur. Classical ILC exhibits behavior similar to other ER positive tumors, showing late rather than early recurrence, and better response to hormonal therapy compared to chemotherapy. ILC shows a different pattern of metastasis than IDC, involving unusual sites such as the gynecologic and gastrointestinal tracts, and peritoneum.