E2674. Invasive Lobular Carcinoma Beyond the Breast: Patterns of Intra-Abdominal Spread and Interpretation Pitfalls
  1. Hannah Fleming; University Health Network
  2. Ciara O'Brien; University Health Network
  3. Vivianne Freitas; University Health Network
Define the incidence of Invasive Lobular Carcinoma (ILC) of the breast, discuss the pathology of ILC and how this affects the appearance of intra-abdominal metastases, outline the distribution and rate of Invasive lobular carcinoma vs Invasive ductal carcinoma metastases, demonstrate the imaging features of intra-abdominal ILC metastases, and highlight the importance of the radiologist in diagnosis, especially due to pathological pitfalls that exist in the differentiation between Signet Ring Gastric Carcinoma and Invasive Lobular Carcinoma metastases.

Educational Goals / Teaching Points
ILC is the second most common breast carcinoma (10%). Intra-abdominal metastases often occurs early in the course of the primary disease. However it can also occur years after the primary diagnosis. Intra-abdominal ILC metastases can often present as a first sign of recurrent disease. ILC is histologically distinct from Invasive Ductal Carcinoma (IDC). More frequently involves the peritoneum, Gastrointestinal, Genitourinary tracts and gynaecological organs. Higher distant metastasis rate due to loss of E - Cadherin, which affects the rate and pattern of spread, with a submucosal pattern of spread most commonly seen. Metastases can appear as a diffuse infiltrative process without a discrete tumor mass.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The key imaging findings include gastrointestinal tract (diffuse infiltration of bowel wall or stomach instead of mural masses Commonly short segment [< 10 cm] More likely multiple sites); ovary (mixed cystic and solid masses [Krukenberg Tumor]); peritoneum (numerous tiny nodules rather than large “omental caking”); retroperitoneum (numerous tiny nodules; infiltration of ureters; can cause hydronephrosis; retroperitoneal adenopathy commonly seen); and hepatobiliary (similar rate and appearance as Invasive Ductal Carcinoma. Multiple enhancing masses Indistinguishable from other metastases Infiltration of the gallbladder wall Can cause acute cholecystitis).

Intra-abdominal metastases from ILC of the breast is critical for the radiologist to recognise because differentiation from site specific primary tumours guides appropriate immunohistochemical staining which is crucial to treatment planning; radiologists can suggest a primary breast malignancy in patients with distant metastases at initial presentation or if this is the first sign of recurrent disease, as can often happen years after the primary diagnosis of breast carcinoma; and pathological pitfalls exist, as it can be histologically identical to signet-ring cell gastric carcinoma. Therefore, vitally important that a suspicion of metastatic Invasive Lobular Carcinoma must be conveyed to pathologist by the interpreting radiologist.