The histogenesis of extragonadal YST remains speculative and controversial. There are four potential mechanisms by which a germ cell neoplasm can arise in the endometrium. The first is the aberrant migration of primordial germ cells in a lateral direction during embryogenesis, which can remain in the basal layer of the endometrium for many years. The second potential mechanism is metastasis from occult ovarian YST. Residual fetal tissues remaining in the uterus because of an incomplete abortion and somatic cells that have undergone aberrant differentiation by which YST originates in unusual sites are the other two potential mechanisms.
We summarized 30 primary endometrial YSTs: the present case and 29 cases from the literature. Patients with pure YSTs were younger than those with a concomitant somatic tumor. Therefore, pure endometrial YST and endometrial YST with somatic tumors may have had different histogeneses. Pure endometrial YSTs may originate from pluripotent germ cells, while endometrial YSTs with somatic tumors may arise from malignant pluripotent somatic stem cells or possibly via “retrodifferentiation”, by which a differentiated cell transforms into a more primitive form. Reports of ovarian YST arising from an endometrioid carcinoma support this hypothesis[8–10]. YSTs of the female genital tract in older adults are commonly derived from somatic epithelial neoplasms.
AFP, a special tumor marker elevated in the vast majority of patients with tumors containing a YST component, is essential for the diagnosis and monitoring of progressiveness. In the overwhelming most endometrial YSTs, AFP is used as a significant follow-up indicator, but only a few patients had normal serum AFP levels .
Since primary endometrial YST is rare, pathologists who lack experience and are not familiar with the morphology of YST may make an incorrect diagnosis, especially in biopsy specimens. Moreover, its immunohistochemical profile overlaps between that of YST and carcinoma. AE1/AE3 is positive in both carcinoma and YST, as observed in the current case, and is not a good marker for differential diagnosis. Both HNF-1β and PAX8 can be positive in YST and thus result in an incorrect diagnosis of clear cell carcinoma. However, both marker commonly are patchy positive in YSTs rather than diffuse positive in clear cell carcinoma. SALL4, as a sensitive marker for germ cell tumors, is a useful marker for diagnosis when combined with GPC-3 and AFP. Hence, a panel of markers is necessary for the diagnosis of YST at rare sites.
Given the rarity of primary endometrial YSTs, there is no consensus on the treatment of this extremely rare tumor. Surgery combined with adjuvant chemotherapy is the main treatment. However, the specific resection range remains controversial, and whether ovaries are preserved still needs further study. Among the 30 patients described herein, unilateral ovary reservation was reported in only one patient, and bilateral ovary reservation was reported in 2 patients,. Rossi described a 30-year-old woman with stage II primary endometrial YST treated with simple total hysterectomy, preserving the bilateral ovary. The patient remained free of disease for more than 6 years after completion of the therapy. Tao reported a similar case, a 27-year-old woman with stage IA disease who remained free of disease for 14 months after surgery. Wang described a 29-year-old woman with stage II disease who preserved her right adnexa to maintain endocrine function and was alive without recurrence for 39 months. This fact revealed the possibility of treating a young patient with early-stage primary YST of the endometrium with surgery to conserve the ovary. The surgeons effectively retained the patient’s ovarian endocrine function and improved her quality of life.
For germ cell tumors, including ovarian YST, the BEP regimen results in high cure rates, even for advanced-stage tumors. However, the outcome for EGYST, especially in endometrial tissue, is less certain. In the literature series, 5/16 (31.3%) patients with pure YST died of disease (range 2 to 24 mo; median, 8 mo), in which 4 of 5 patients were FIGO stage IV, 1 received a regimen of vincristine, vinblastine and cyclophosphamide, 1 (6.2%) was alive with disease (follow-up, 8 mo), and 10/16 (62.5%) had no evidence of disease (range 6 to 72 mo; median follow-up 19 mo). Of the patients in whom an associated somatic tumor was reported, 3/10 (30%) died of their disease, 5/10 (50%) were alive with disease, and only 2/10 (20%) had no evidence of disease. There are too few cases to determine whether the poor prognosis is related to a somatic origin or to the fact that 6/8 (75%) of those who died of disease had FIGO stage III or IV at presentation. These findings suggest that tumor staging and somatic components are 2 important factors that influence the prognosis of patients with endometrial YST, and patients with YST of somatic origin may have a poor prognosis.