Rare Presentation of Metastatic Breast Cancer Involving the Peritoneal Cavity: Two Cases Arising From Stage 0/1 Disease

Ductal cell carcinoma in situ (DCIS) is a noninvasive stage 0 breast cancer that arises from an abnormal proliferation of ductal epithelial cells. If untreated, it can progress to invasive ductal carcinoma (IDC), the most common form of breast cancer. A minority of women with early-stage breast cancer may experience recurrent advanced cancer, which can progress to metastatic disease, commonly in the bone, liver, lung, and brain. Improved surveillance and raised awareness over the last three decades have resulted in an increased incidence of disease; however, early detection and treatment of DCIS and IDC have a favorable prognosis. We present two cases of well-treated early-stage breast cancer with late recurrence of distal metastasis involving the peritoneal cavity and liver, with ascites as a primary presentation. In Case one, Stage 1 IDC was detected on a routine mammogram and was well-treated with lumpectomy and sentinel lymph node biopsies, chemotherapy, and radiation, with repeat mammograms negative for any evidence of recurrence. One year following treatment, the patient presented with dull epigastric pain and ascites positive for malignancy, with primary breast origin. In Case two, the patient presented to the emergency department with right upper quadrant pain and abdominal distension. A CT scan identified multiple liver lesions, and a biopsy revealed primary breast origin. A subsequent mammography detected DCIS in the right breast. One month later, the patient presented with abdominal and pelvic ascites and rapid decline of mental status before treatment was initiated. These cases underscore the importance of educating patients on self-examinations and yearly mammograms. Additionally, it is essential to educate providers on risk factors of metastatic disease and their possible presentations, including metastasis into the peritoneal cavity, to ensure optimal clinical outcomes.