Abstract
Metastatic adenocarcinoma to the breast from an extramammary site is extremely rare. In the literature, the most current estimate is that extramammary metastases account for only 0.43% of all breast malignancies and that, of these extramammary sites, colon cancer metastases form a very small subset. Most commonly seen metastasis in breast is from a contralateral breast carcinoma, followed by metastasis from hematopoietic neoplasms, malignant melanoma, sarcoma, lung, prostate, and ovary and gastric neoplasms. Here we present two rare cases, in which colonic adenocarcinomas were found to metastasize to the breast. In both cases, core biopsies were obtained from the suspicious areas identified on mammogram. Histopathology revealed neoplastic proliferation of atypical glandular components within benign breast parenchyma which were morphologically consistent with metastatic adenocarcinoma. By immunohistochemical staining, it was confirmed that the neoplastic components were immunoreactive to colonic markers and nonreactive to breast markers, thus further supporting the morphologic findings. It is extremely important to make this distinction between primary breast cancer and a metastatic process, in order to provide the most effective and appropriate treatment for the patient and to avoid any harmful or unnecessary surgical procedures.
Highlights
Colorectal cancer is the third most common type of cancer globally, and most frequently it spreads to the regional lymph nodes, liver, lungs, and bone, in descending order [1]
It is very rare to find metastasis of colonic adenocarcinoma to the breast and, they often may be confused with primary neoplasms of the breast [2]
Anti-cytokeratin 7 (CK 7) and anti-cytokeratin 20 (CK 20) antibodies have been used to differentiate between cancers of a primary or metastatic source [2]
Summary
Colorectal cancer is the third most common type of cancer globally, and most frequently it spreads to the regional lymph nodes, liver, lungs, and bone, in descending order [1]. It is very rare to find metastasis of colonic adenocarcinoma to the breast and, they often may be confused with primary neoplasms of the breast [2]. The first described case of colon cancer metastasizing to the breast was reported in 1974 by McIntosh and, since that time, there are only a few reported cases in the literature [4]. It is necessary to identify the source of the tumor accurately, in order to determine the most appropriate line of treatment for the patient and, to avoid any unnecessary radical surgery [5, 6]. We have described two cases of adenocarcinoma of colorectal origin that spread to the unilateral breast with distinguishing histologic and immunohistochemical features between primary breast malignancies and metastatic adenocarcinoma of colorectal origin
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