Metastasis to the breast from extramammary malignancies is rare. Nevertheless, its recognition is important because the prognosis and treatment differ from that of primary breast cancer. We report a unique case of primary peritoneal serous carcinoma that initially presented as inflammatory breast cancer. The patient received neoadjuvant chemotherapy for breast cancer and subsequently underwent bilateral total mastectomy and bilateral sentinel lymph node biopsy. She was found to have extensive intralymphatic carcinoma in both breasts, with only focal minimal breast parenchymal involvement, and residual metastatic carcinoma in bilateral sentinel lymph nodes. Further work-up revealed pelvic ascites and omental nodularities. The patient underwent laparoscopic bilateral salpingo-oophorectomy, which revealed high-grade serous carcinoma involving both ovaries and fallopian tubes. Molecular testing of tumor from the ovary and axillary lymph node showed an identical pattern of allelic loss, confirming a common origin for both tumors. To our knowledge, this is the first reported case of an extramammary primary malignancy that not only presented as inflammatory breast cancer but also was diagnosed and initially treated as such.