In the stratified analysis by histological type, HER2 expression was associated with worse OS of unclassified ovarian cancer (n = 30, HR = 1.55, 95% CI = 1.29 to 1.88, H2 = 1.7; I2 = 63.7%, 95%CI = 46% to 75%), while HER2 expression implied no significant association in serous ovarian cancer (n = 4, HR = 1.65, 95% CI = 0.83 to 3.27, H2 = 2; I2 = 76%, 95%CI = 34% to 91%) (Fig 3). Here, ERBB2 is linked to ovarian serous adenocarcinoma.