Müllerian-type high-grade serous carcinoma presenting exclusively with pleural lesions and no detectable abdominopelvic primary tumor: a case report

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Müllerian-type high-grade serous carcinoma (HGSC) most commonly originates from the fallopian tube, ovary, or peritoneum and usually presents with abdominopelvic disease. Thoracic presentation without a detectable abdominopelvic primary tumor is extremely rare and poses a diagnostic challenge. We report the case of a 60-year-old woman who was referred to our hospital after pleural thickening was detected during a routine medical checkup. Chest computed tomography (CT) revealed left pleural thickening with mild pleural effusion. Thoracoscopic pleural biopsy was performed. Histopathological examination demonstrated spindle-shaped cells with mild nuclear atypia, with scattered calcifications and osteocyte-like elements. Immunohistochemical staining showed positivity for PAX8, WT-1, AE1/AE3, CK7, p16, and p53, and negativity for calretinin, D2-40, TTF-1, and Napsin A, supporting a Müllerian-type HGSC. Diagnostic/staging laparoscopy with bilateral salpingo-oophorectomy revealed no macroscopic tumor or disseminated lesions. Both ovaries and fallopian tubes were carefully examined pathologically, with the fallopian tubes examined using the SEE-FIM protocol. No malignant lesion or serous tubal intraepithelial carcinoma (STIC) was identified. Peritoneal washing cytology was negative. p53 and Ki-67 immunohistochemistry of the tubo-ovarian specimens was not performed. The absence of a detectable abdominopelvic primary tumor after radiological, laparoscopic, and pathological evaluation suggests an extremely rare thoracic presentation of Müllerian-type HGSC. Both ovaries and fallopian tubes were carefully examined pathologically, including examination of the fallopian tubes using the SEE-FIM protocol, and no malignant lesion or STIC was identified. Nevertheless, an occult microscopic Müllerian primary cannot be completely excluded, particularly because p53 and Ki-67 immunohistochemistry of the tubo-ovarian specimens was not performed. Primary pleural Müllerian carcinoma, EOPPC, and Müllerian-type HGSC of undetermined primary origin therefore remain possible classifications. Müllerian-type HGSC should be considered in the differential diagnosis of pleural tumors in women, even when no abdominopelvic primary tumor is identified. Comprehensive radiological, laparoscopic, and pathological evaluation is important for determining the most appropriate classification. In the absence of an identified primary site, classification should remain cautious, and EOPPC should be regarded as a possible interpretation rather than a definitive diagnosis.