Mixed epithelial-stromal tumor (MEST) of seminal vesicle: a proposal for unified nomenclature.

In contrast to the common tumors of the prostate, seminal vesicle demonstrates low potential for neoplastic proliferation. Of the rare primary seminal vesicle tumors, adenocarcinoma is the most common, but there are also rare seminal vesicle neoplasms which demonstrate epithelial and stromal components. These neoplasms have been described in the literature under various names, including "epithelial-stromal tumor," "cystic epithelial-stromal tumor," "cystadenoma," "cystomyoma," "mesenchymoma," "Müllerian adenosarcoma-like tumor," "phyllodes tumor," and "cystosarcoma phyllodes." The spectrum of reported mixed epithelial-stromal tumors (MEST) of seminal vesicle encompasses low, intermediate and high-grade tumors, but the precise distinction and nomenclature for these tumors remain unsettled. We propose a common nomenclature for these tumors, based on the review of published cases and 2 index cases from our practice, which represent the low-grade category. The first patient was 46 years old and presented with seminal vesicle neoplasm detected on routine rectal examination. The neoplasm measured 4 cm in greatest dimension, and completely replaced the left seminal vesicle. The tumor was circumscribed and consisted of multiple cysts separated by spindle-cell stroma. The second patient was a 60-year-old man, who had an incidental seminal vesicle neoplasm, which was discovered when he underwent a radical prostatectomy for a prostatic adenocarcinoma, (Gleason score 3+4, stage 3a). Both neoplasms contained hypercellular stroma, which was composed of uniform spindle cells, arranged in fascicles and interspersed between the glands. Both tumors lacked worrisome morphology, such as infiltrative borders, cell atypia, increased mitotic activity, hemorrhage, and necrosis. The stromal cells were reactive for estrogen and progesterone receptors, and desmin. The cysts and dilated glands were lined by epithelial cells, which were positive for cytokeratin 7 and were negative for prostate-specific antigen and prostate-specific acid phosphatase. The first patient underwent prostatectomy and was alive and without evidence of disease recurrence or progression after 11 years of follow-up. Similarly, the second patient had no evidence of disease recurrence or progression after 8 months of follow-up. We propose that term seminal vesicle "mixed epithelial-stromal tumor" be used to designate the tumors of the seminal vesicle containing epithelial and stromal components, with a distinction of grade based on the histologic features and the biological behavior. Histologic features to be evaluated for grade separation include stromal atypia, mitotic activity, nuclear pleomorphism, and tumor necrosis. Designations "low-grade MEST," "intermediate-grade MEST (uncertain malignant potential)," and "high-grade MEST" of seminal vesicle can be applied to these tumors to better characterize and study them in the future.