In 556 patients undergoing surgery for ovarian cancers the frequency o
f endometriosis ranged from 3.6% to 5.6% in serous, mucinous, and misc
ellaneous neoplasms versus 26.3%, 21.1%, and 22.2%, respectively, in e
ndometrioid, clear cell, and mixed subtypes; the differences were stat
istically significant (chi2 heterogeneity 50.0, p < 0.001) and consist
ent in strata of age, parity, menopausal status, and disease stage.