Stemness in high-grade serous carcinoma of tubo-ovarian origin causes multiple immunohistochemical pitfalls: a case report.

High-grade serous carcinoma (HGSC) of tubo-ovarian origin is a malignant neoplasm with heterogeneous morphology. This intratumour morphological heterogeneity comprises various architectural patterns and diverse cytological aspects, which often coexist within a single tumour.1 Although HGSC is characterised by a high mitotic rate and substantial nuclear pleomorphism, architecturally and/or cytologically diverse areas can cause diagnostic confusion.1 The current case illustrates that clear cell changes in HGSC can provoke ‘blunderbuss immunohistochemistry’,2 leading the pathologist astray and resulting into academic referral because of unexpected staining patterns. A woman in her 70s underwent a bilateral salpingo-oophorectomy because of an enlarged right ovary. This ovary contained a predominantly solid and partially cystic mass, measuring 4.5×3×2.5 cm. The left ovary and both Fallopian tubes did not show any anomalies. Peritoneal carcinomatosis was not observed. Histopathological evaluation of the left ovary and both Fallopian tubes was normal. Sampling of the unilateral right ovarian mass revealed a neoplasm with prominent cytonuclear atypia, numerous mitoses (including several atypical mitotic figures) and extensive necrosis. The tumour had a mixed solid, cribriform and glandular architecture. Because of some solid clear cell areas, immunohistochemical stainings for CD117 and placental alkaline phosphatase (PLAP) had initially been performed …