The surface epithelium of the ovary, which is considered as the source of common epithelial tumors of the ovary, can differentiate into squamous cells. Primary squamous cell carcinoma (SCC) of the ovary can occur as an endometriosis, teratoma, or Brenner’s tumor [2, 3]. However, we found no evidence of these.
A typical area of OSC was confirmed, as demonstrated by its solid growth morphology, marked pleomorphism, and prominent nucleoli with numerous mitotic figures. However, the ovarian tumor described here bore some resemblance to SCC in terms of its morphological character. Thus, we used several immunohistochemical markers, such as PAX8, p16, p53, WT1, ER, p63, and CK5/6, to make a distinction between the primary OSC and ovarian metastatic SCC.
The IHC p53/p16 index was a good marker for high-grade OSC, which are defined as tumours with diffuse p53 expression or complete absence of p53 expression (null type) associated with diffuse p16 expression . Notably, p16 overexpression is more frequently found in serous carcinomas . p53, a tumour suppressor gene, is typically overexpressed in OSC and is regarded as a useful marker of such carcinomas [4, 6]. TP53 gene mutations are present in nearly 100% of high-grade OSCs . WT1 has been proved to play an important role in the normal development of the kidneys and gonads and more usually found in OSC. It’s location in the female genital tract is usually used to distinguish SOC from other tumour types . In the female genital tract, WT1 expression is usually used to distinguish OSCs from other ovarian tumour types [4, 7]. ER reactivity was demonstrated in almost all the OSC, but most of SCCs were negative for ER [8, 9]. Moreover, expression of PAX-8 confirmed that the tumour originates from female genital tract, such as the ovaries, uterus, and fallopian tubes . p63 and CK5/6 are typically expressed in human squamous epithelium and SCC, but not OSC .
PAX8, p53 (mutations), WT1, and p16 were positive in most ovarian tumor cells described herein, which is a typical feature of OSC. Interestingly, the tumor cells with severe nuclear pleomorphism and eosinophilic cytoplasm also showed intense cytoplasmic CK5/6 expression and strong nuclear p63 staining. Such a finding of immunohistochemical staining is sufficient to constitute evidence of both patterns of OSC and SCC. Interestingly, the Ki67 index significantly decreased in the squamous differentiation area, which indicate a decreased activity.
We reviewed the current English literature and found only 3 similar cases [1, 2]. The clinical and pathological features were summarized in Table 1. Ulbright et al.  first described two cases of OSC with squamous differentiation that were confirmed by the immunohistochemical markers 35βH11 and 34βE12, and by electron microscopy. Squamous carcinoma arising in association with an OSC was recently reported in a 72-year-old woman . Histological and immunochemical studies have confirmed distinct areas of OSC and SCC, and several small foci of the tumor showing transitional features between serous and squamous differentiation may also be seen. Interestingly, OSC with extensive squamous differentiation occupied the main part of the tumor in our case, arguing for a metaplastic origin of one component from a subset of the original neoplasm. Given the serous morphology and immunohistochemical profile of regions, coupled with no evidence of endometriosis, teratoma, or Brenner’s tumor, we confirmed that the present case provides evidence of a high-grade OSC differentiating into an aggressive SCC.