Nongynecologic metastases to fallopian tube mucosa: a potential mimic of tubal high-grade serous carcinoma and benign tubal mucinous metaplasia or nonmucinous hyperplasia.

Mucosal alterations of the fallopian tube are generally thought to represent alterations of the native tubal mucosal epithelium, whether benign or malignant. The current paradigm implicating the fallopian tube fimbriae as the origin of most pelvic high-grade serous carcinomas (HGSCs) is based on the premise that HGSC growing within the tubal mucosa originated there. This has fueled proposals to redefine classification rules for assigning the primary site of origin on the basis of the presence or absence of HGSC in the tubal mucosa. The corollary is that it is unlikely for metastatic carcinoma to grow within fallopian tube mucosa. Evidence to support or refute this corollary is minimal, in part because the fallopian tubes historically have been ignored. This study reports the pattern and topography of 100 nongynecologic cancers that metastasized to the fallopian tubes. Most tumors were adenocarcinoma (87%), and the remainder included lymphomas, neuroendocrine tumors, and mesotheliomas. The most common primary origins of tumor were the colon (35%) and breast (15%). Gross evidence of a tubal nodule or mass was only seen in 35% of cases. Ovarian metastases were present in 95% of cases, although 23% did not exhibit gross evidence of metastasis. Tumor involved the fimbriae in 49% of cases, including 10% of cases in which the tumor was restricted to the fimbriae without involving the nonfimbriated portion of the tube. The anatomic distribution of metastases included the tubal mucosa (29%), submucosa (43%), muscularis (54%), serosa (76%), lymphovascular spaces (38%), intraluminal space (16%), and mesonephric remnants (39%). The most common architectural pattern of mucosal growth was a flat layer (22/29 cases), followed by varying degrees of stratification, tufting, and papillary growth. High-grade atypia was present in 18/29 cases of mucosal growth, resulting in patterns that resembled primary tubal HGSC. Accompanying growth in the tubal submucosa frequently produced a pseudoinvasive pattern mimicking invasive tubal HGSC. Immunohistochemical expression of p53 by 8/18 high-grade mucosal metastases further contributed to the resemblance to primary tubal HGSC. Bland cytology was present in 11/29 cases of mucosal growth, some of which also exhibited mucinous features, resulting in patterns that resembled either tubal mucinous metaplasia or nonmucinous tubal hyperplasia. Although uncommon, it is possible for metastases of nongynecologic cancers to grow within the mucosa of the fallopian tube and create a potential diagnostic pitfall. Intramucosal growth of a tumor in the fallopian tube is not pathognomonic of a primary tubal origin of the tumor. These findings may carry implications for proposed criteria using the status of the fallopian tube mucosa to assign primary origin of a gynecologic cancer.