A Case Report of Benign Granulosa Cells within the Fallopian Tube Mimicking Malignancy Granulosa cells are ovarian, sex-cord stromal derived cells which surround and support the developing follicle. Foci of extra-follicular granulosa cells have been rarely reported and may represent a significant diagnostic challenge and potential pitfall, especially in the setting of a previous history of malignancy. Here we present a case of benign, displaced granulosa cells within the fallopian tube mimicking malignancy. A 39 year old female with a history of pancreatic gastrinoma and node-positive lobular breast carcinoma was scheduled for total abdominal hysterectomy and bilateral salpingectomy for abnormal uterine bleeding; intraoperative discovery of bilateral ovarian cysts prompted the inclusion of a bilateral cystectomy, in addition to the planned procedure. Gross examination of the submitted specimens demonstrated only uterine leiomyomata, fragments of thickened ovarian cyst wall with a small amount of normal, attached ovary and no remarkable findings associated with the fallopian tubes. Microscopic examination confirmed the gross findings of uterine leiomyomata and ovarian corpora lutea cysts. Additionally, a small (1mm) focus of monomorphic, polygonal-shaped cells with scattered, mildly grooved nuclei and coincident glandular structures filled with eosinophilic material, suggesting Call-Exner bodies, was present within the right fallopian tubal stroma, reaching to the surface epithelium. Given these findings and the patient’s significant history of malignancy, our differential included granulosa cell tumor, metastatic lobular carcinoma of the breast, neuroendocrine tumor and displaced benign granulosa cells. Subsequent immunohistochemical staining supported a diagnosis of displaced, benign granulosa cells. The cells stained positively for inhibin and pancytokeratin (Lu-5) in a dot-like pattern, consistent with granulosa cells, while staining negative for CD56, CK7, synaptophysin and chromogranin, consistent with a diagnosis of benign, displaced granulosa cells. The finding of benign, displaced granulosa cells is a rare but potentially hazardous one, for both the pathologist, as well as the patient. Foci of extra-follicular granulosa cells have been independently reported as mimics of several malignant entities including granulosa cell tumor, ovarian serous carcinoma, small cell carcinoma and lobular breast carcinoma. In all but one of these cases the patient demonstrated a relevant clinical history of malignancy, further complicating the matter; the remaining case, although lacking a history of malignancy, was ultimately signed out as a granulosa cell tumor leading to an unnecessary bilateral oophorectomy. This unfortunate case highlights the need to correctly identify and characterize these cells. Here we have reported a case of benign, displaced granulosa cells within tubal tissue mimicking malignancy in a patient with a significant clinical history. This is one of only a handful of such cases reported in the literature, and only one of three noted to occur within the fallopian tube. Continued and increased recognition of this rare but treacherous phenomenon will help to lessen its potential deleterious impact on pathologic reporting and patient care.