Ultrastructural study of benign, low-malignant potential (LMP), and malignant ovarian tumors.

Ultrastructural characteristics of benign, low-malignant potential (LMP), and malignant ovarian tumors were investigated, considering the aspects of histologic subtypes and histologic grading. In addition, the histogenesis of ovarian cancer was histologically investigated in an attempt to elucidate whether malignant tumor was generated from benign or LMP tumor, or whether it was generated de novo from normal tissues. Although all the benign, LMP, and malignant tumors appeared to be derived from Mullerian duct in serous tumors, the origin of endometrioid or mucinous tumor could not be ultrastructurally clarified. However, there was ultrastructural similarity between benign and malignant tumors among serous, endometrioid, and mucinous tumors, and it was suggested that benign adenoma may be the developmental origin of malignant tumors regardless of the histologic subtype. In addition, the investigation of endometrioid tumors revealed that the differences of histologic grading in malignant tumors reflected the ultrastructural differences, and that G1 tumor had an ultrastructure that was more similar to that of benign and LMP tumors than to that of G2 tumor.