Primary Rectal Adenocarcinoma Metastasizing to Bilateral Breasts – a Rare Case Demonstrated by 18 F-FDG PET/CT

Abstract

A 22-year-old female presented with multiple painless bilateral breast masses for the past 2 months. On further questioning, she had hematochezia and constipation for three months. On digital rectal examination, thickening of rectal mucosa at 5 cm from the anal verge was found. On physical examination, multiple firm, non-tender, nodular lesions were found in bilateral breasts. Contrast-enhanced computed tomography (CECT) sagittal, coronal and axial images of the abdomen showed mass-like circumferential wall thickening in the rectum extending to the recto-sigmoid junction, which was suggestive of a primary malignant lesion (Fig. 1a-d, arrows). Sigmoidoscopy showed circumferential growth involving the rectum up to the rectosigmoid junction. Histopathology from the rectal lesion revealed signet ring cell adenocarcinoma. Mammography was performed and the differential diagnoses were primary breast malignancy, bilateral fibroadenoma and metastatic breast disease. 18 F-FDG PET/CT was done to determine the extent of the disease. Maximum intensity projection images of FDG PET showed linear diffuse increased FDG uptake involving the rectal region (Fig. 2a, arrow head), multiple areas of increased FDG uptake in the bilateral breast region (Fig. 2a, arrows), and patchy focal areas of increased FDG uptake in multiple dorso-lumbar vertebrae, multiple bilateral ribs, bilateral scapulae, the humerus, the pelvic bones, the left femur proximal shaft and in the left paravertebral region. Sagittal sections of fused 18 F-FDG PET/CT images (Fig. 2b) show subtle lytic changes with increased FDG uptake in multiple cervico-dorsal and lumbar vertebrae and the sternum, and Fig. 2c (arrow) shows circumferential thickening of the rectum with increased FDG uptake. Axial sections of fused PET/CT images (Figs. 2d, e) show multiple FDG-avid soft tissue density lesions involving bilateral breast parenchyma. 18 F-FDG PET/CT findings were suggestive of an active primary malignant disease involving the rectum with a metastatic disease involving extensive skeletal sites, bilateral breasts and retroperitoneal lymph nodes.A biopsy taken of bilateral breast masses showed a malignant tumor comprising of neoplastic cells in sheets with intracellular mucin and eccentrically pushed pleomorphic nuclei (signet ring cells) along with pools of extracellular mucin in hematoxylin and eosin-stained sections (Figs. 3a, b; 40X) which was consistent with metastatic signet ring cell adenocarcinoma to both breasts.Metastatic breast disease from extramammary primaries is uncommon and it constitutes 0.5 -6 % of all breast malignancies [1,2]. Melanomas, lymphomas, leukemias, and sarcomas are the most common malignancies causing breast metastases. Infrequently, carcinomas of the lung, stomach, ovary, liver, tonsil, pleura, pancreas, cervix, perineum, endometrium, bladder, carcinoid tumors, and renal cell carcinomas can cause metastatic breast disease [3][4][5][6]. Bilateral breast metastases are very rare and are reported in few cases of ovarian carcinoma [6]. Rectal aden...