When Breast Cancer Hides Elsewhere: Invasive Lobular Carcinoma Presenting as Gallbladder Disease.

Invasive lobular carcinoma is a type of breast cancer that is distinctive in morphology. Due to this, invasive lobular carcinoma often proves to be difficult for clinicians to detect and treat before metastasis occurs. While invasive lobular carcinoma shares common metastasis locations with other breast cancers, such as infiltrating ductal carcinoma, invasive lobular carcinoma is notorious for presenting in abnormal sites. This report will introduce an atypical case of invasive lobular carcinoma first discovered in the gallbladder. A 58-year-old female presented to the emergency department with a one-week history of right upper quadrant pain. After an ultrasound revealed multiple stones within the gallbladder, she underwent an elective cholecystectomy. Pathology showed findings indicative of invasive lobular carcinoma of the breast. A follow-up mammogram and ultrasound showed no abnormalities of the breasts; however, a PET/CT scan revealed an area of abnormal metabolic activity in the right breast. Subsequent genetic testing unveiled a missense mutation in the CDH1 gene. We will discuss the atypical findings of this presentation of invasive lobular carcinoma, specific genetic markers associated with this type of malignancy, and the unique features of this type of cancer that render early detection difficult.