An immature inhibin-α-expressing subpopulation of ovarian clear cell carcinoma cells is related to an unfavorable prognosis.

Inhibin-α, a member of transforming growth factor-β, is elevated in multiple tumors, but its specific roles are poorly understood. Here, we examined the feature of inhibin-α-expressing cells in ovarian tumors. Immunohistochemically, inhibin-α-expressing tumor cells were detected only in ovarian clear cell carcinoma (OCCC) among various types of ovarian tumors. By comparing the expression of inhibin-α and Ki-67, inhibin-α-expressing tumor cells were revealed to be less proliferative. When spheroids and chemoresistant cells were derived from OCCC cell lines, the expression level of inhibin-α was elevated, and that of an immature marker, aldehyde dehydrogenase, was also elevated. In consistent with this, inhibin-α expression was correlated with other immature markers, such as OCT3/4 and SOX2, and inversely correlated with proliferative marker MKI67 in public database on OCCC. Knockdown of inhibin-α in OCCC cell decreased chemoresistance. Moreover, prognostic analysis with 69 surgically resected OCCC cases revealed that the increased inhibin-α expression was an independent unfavorable prognostic factor. These findings suggested that inhibin-α-expressing subpopulation of OCCC tumor cells appeared to be less proliferative, immature, and angiogenic and to be related to acceleration of malignant progression.