Primary small cell carcinoma of the ovary is a very rare and highly malignant tumor often associated with hypercalcemia, first reported by Dickersin in 1982, and only 36 cases were reported in the world literature from 1982 to 1991 according to Taraszewi et al. The histogenesis of the few small cell carcinomas of the ovary reported in China is still a mystery because of the relatively small tumor cells and the ultrastructural epithelial nature (pontine granule-like junction of the basement membrane). Therefore, the name of this non-specific small cell carcinoma is tentative, and the exact histological nomenclature needs to be further discussed by pathologists. Clinical manifestations 1. Hypercalcemia: All 11 patients collected by Diekersin et al. in 1982 had hypercalcemia, and about 2/3 of the later reported cases had combined hypercalcemia [serum calcium values 2.94-4.49 mmol/L (11.8-18.0 mg/dl)]. Serum phosphorus values can be normal or below normal. Blood calcium and phosphorus values return to normal within a short period of time after tumor resection and become abnormal again with tumor recurrence and metastasis. Serum parathyroid hormone (PTH) values are normal. Serum calcium and phosphorus can be used as a reliable indicator to monitor tumor activity. 2. Symptoms and signs: Common symptoms and signs include abdominal distension, abdominal pain, lower abdominal mass, ascites, etc., which are not specific. The vast majority of tumors occur in the unilateral ovary, and the incidence of both sides is almost equal (Kathleen, 1988). The peritoneum is the best site for metastasis, and there can be pelvic and abdominal lymph node metastasis and distant metastasis such as liver, lung and pleura. In some tumors, fibers are shown to surround larger nests of cells, while in others, fibers are shown to reach between tumor cells and irregularly and incompletely surround individual cells. Aguirre et al. had 6, 12 and 15 positive for 3 cytokeratins (AE-1/AE-3902CAM 5.2), 5 positive for epithelial tumor-associated antigen (EMA) and 8 positive for vimentin in 15 cases. Neurospecific enolase (NSE) was positive in 10 cases. These immunohistochemical results failed to reveal the tissue origin of small cell carcinoma, and there were no specific findings. 2. Other adjuvant examinations: electron microscopy: the diameter of small tumor cells ranged from 6.3 to 15.0m [mean (10.9±1.8)m] some large tumor cells were 12.5 to 23.8m [mean (15.5±3.5)m] in diameter. The cell clusters had interrupted basal lamina at the periphery and desmosomelike junction between the cells. The nuclei were relatively large with abundant euchromatin and a few scattered patches of heterochromatin. The most diagnostic feature is the abundance of pools and vesicles formed by the expansion of the rough endoplasmic reticulum, which is filled with fine particles of light to moderate electron density. most of the RER pools or vesicles are 0.4-2.4 m in diameter, and a few are up to 10-12 m in diameter. the nuclei are distorted and displaced by them. In tumors with or without hypercalcemia, RER pools and capsules do not differ morphologically or quantitatively, and this feature is often clearly discernible in common specimens embedded in formalin-ethanol (formalin)-fixed paraffin. Other cell plasma components include abundant polyribosomes, mitochondria, and small amounts of Golgi complexes. Some cells are rich in lipid droplets, lysosomes, etc. Some cells have a small amount of microvilli on the free surface (Mcmahon, 1988) Individual tumors have a small amount of neuroendocrine-like dense granules (Fortune, 1986) In some larger cells, there are more free ribosomes, RER capsules, and no components different from small cells are identified. III. Diagnosis Young women with unilateral adnexal masses combined with hypercalcemia, if no hypercalcemia or no hypercalcemia is found then it is difficult to get a definite diagnosis before surgery. This tumor should be highly suspected except for parathyroid bone disorders and ovarian anaplastic cell tumors, although a few ovarian plasmacytic papillary cystic adenocarcinoma and malignant lipoblastoma may also be combined with hypercalcemia, but at an older age. Differential diagnosis: Granulosa cell tumor, metastatic small cell carcinoma and malignant lymphoma are easily confused with this tumor histologically. 1. Granulosa cell tumor: The tumor cells are larger than this tumor, with nuclear grooves and obvious fibroma-like and follicular membrane tumor-like components. In the comparison of immunohistochemical staining of granulosa cell tumor and this tumor by Aguirre, EMA was negative in the former and positive in the latter; vementin was positive in the former and positive in the latter, and the rate of positive in the latter was 1/2. The unique RER macrocapsules in the ultrastructure of this tumor also help to differentiate them. 2. Metastatic small cell carcinoma: The histology of small cell carcinoma of the cervix and endometrium is the same as that of small cell carcinoma of the lung (oat cell carcinoma) with the presence of silver-loving granules in the cell plasma under light microscopy and cytoplasmic protrusions and dense granules with membranes (neuroendocrine granules) in the ultrastructure under electron microscopy, which are called neuroendocrine tumors (APUD) tumors) (Ibrahim 1984; Kunlar, 1984; Young1985; Gersell, 1988). In contrast, in primary ovarian small cell carcinoma, no features of neuroendocrine tumors were found, except for a few dense granules in individual tumors. 3. Malignant lymphoma: immunohistochemical staining for specific antibodies to lymphocyte markers and electron microscopic observation are different from this tumor. V. Prognosis The disease is highly malignant and has an extremely poor prognosis. Although 2/3 of patients are in clinical stage I at the time of initial surgery, their disease progresses rapidly Taraszewski (1991) reported that the average survival time after surgery was only 18 months; Young reported that the average 5-year survival rate was only 10%, and even for stage Ia patients, it was only 30% Seedman (1995) reported that 20 cases of small cell carcinoma of the ovary survived for 2 years Tewari et al. (1997) reported a case of stage IIIc ovarian small cell carcinoma who survived tumor-free for 5 years after surgery and combination chemotherapy with cisplatin; Powell et al. (1998) also reported a 21-year-old patient with stage IIIc ovarian small cell carcinoma who underwent adnexal resection and tumor reduction with preservation of the uterus and the opposite side of the ovary. The patient survived tumor-free for more than 2 years after aggressive combination chemotherapy.