. 2017 Dec 5;28(Suppl 8):viii8–viii12. doi: 10.1093/annonc/mdx445

Table 2.

Major changes in WHO classification and supporting reasons

Major changes	Supporting reasons
Formal adoption of the two-step grading system	Supported by science
Papillary cystic BOT → SBOT/atypical proliferating tumor	Cystic serous tumor with >10% BOT is now SBOT
Papillary surface BOT → SBOT, micropapillary type, noninvasive LGSOC	High risk of peritoneal implants (27 versus 13%) for micropapillary; 50% probability LGSOC in peritoneal SBOT base
‘Grade 2’ tumors are candidates for p53 immunostaining	Likely HGSOC, support by p53 staining
Endocervical MBOT → seromucinous	Resembles SBOTs with one-third associated with endometriosis and ARID1a^mut

BOT, borderline ovarian tumor; MBOT, mucinous borderline ovarian tumor; SBOT, serous borderline ovarian tumor; HGSOC, high-grade serous ovarian carcinoma; LGSOC, low-grade serous ovarian carcinoma.