Infiltrating Lobular Carcinoma of the Breast - A Palpable Finding on a Patient with Negative Mammogram.

Introduction: Breast cancer is the most common cancer diagnosis amongst US women and has several subtypes1. Invasive lobular carcinoma of the breast is the second most common subtype of invasive breast tumors after invasive ductal carcinoma, accounting for approximately 5-15% of cases. ILC is a cancer that begins in the milk producing lobules and subsequently invades the fibrous/fatty tissue of the breast2. ILC frequently fails to form a palpable mass on physical exam and has atypical imaging findings, which makes it a diagnostic challenge3. Case Description: 89-year-old female with no family/personal history of breast cancer presented with a palpable left breast lump for undetermined period of time. Diagnostic mammogram was performed and yielded no abnormality. Ultrasound evaluation of the bilateral breasts revealed a left antiparallel hypoechoic irregular mass at 2:00 position, 12 cm from the nipple with posterior acoustic shadowing. Ultrasound-guided core biopsy was recommended and revealed ER/PR+ infiltrating lobular carcinoma. Patient underwent successful lumpectomy and received breast radiation. Discussion: ILC poses a diagnostic challenge, both clinically and radiographically. The low density of tumor cells and lack of desmoplastic stromal reaction make ILC difficult to detect on both physical exam and mammography2. In mammography, the most common manifestation is a mass with ill-defined borders followed by architectural distortion. In ultrasound, it commonly presents as an irregular mass with posterior acoustic shadowing3. Treatment involves a multidisciplinary approach including radiologic analysis, surgical consultation, and medical oncologic management. Patients will often require preoperative MRI, followed by resection and neoadjuvant chemotherapy/radiation with possible hormonal therapy4.