Identification of intranuclear inclusions is useful for the cytological diagnosis of ovarian clear cell carcinoma

Objective The aim of this study was to clarify the diagnostic significance of the presence of intranuclear inclusions in clear cell carcinoma (CCC). Materials and Methods We analyzed 98 imprint specimens and 53 ascites specimens from 98 ovarian carcinoma cases [28 CCCs, 37 serous carcinomas (SCs), 22 endometrioid carcinomas (ECs), and 11 mucinous carcinomas (MCs)]. We examined (1) frequency of intranuclear inclusion-positive cases of each ovarian carcinoma subtype, using imprint specimens, (2) frequency of intranuclear inclusion-positive cells of each ovarian carcinoma subtype, using imprint specimens, (3) frequency of intranuclear inclusion-positive cases of each ovarian carcinoma subtype, using ascites specimens, and (4) sensitivity and specificity of the presence of intranuclear inclusions for the cytological diagnosis of CCC. Results (1) The frequency of intranuclear inclusion-positive cases in CCC (96.4%) was significantly higher than in SC (13.5%), EC (13.6%), and MC (18.2%) (P < 0.001). Two or more intranuclear inclusions in a single nucleus were observed only in CCC. (2) The frequency of intranuclear inclusion-positive cells in CCC (median, 0.41%) was significantly higher than in non-CCC subtypes (0.010%) (P < 0.001). (3) Using ascites specimens, the frequency of intranuclear inclusion-positive cases in CCC (78.6%) was significantly higher than in SC (10.3%), EC (0%), and MC (0%) (P < 0.001). (4) The sensitivity of intranuclear inclusions was 96.4%, and the specificity was 85.7%. Conclusions The identification of intranuclear inclusions, in particular a high frequency and multiple intranuclear inclusions in a single nucleus, is useful for the cytological diagnosis of CCC. Furthermore, these results may be applicable to ascites cytology.