Classification systems in Gestational trophoblastic neoplasia: Sentiment or evidenced based?

The classification system for Gestational trophoblastic neoplasia (GTN) has proved a controversial topic for over 100 years. Numerous systems simultaneously existed in different countries, with three main rival classifications gaining popularity, namely histological, anatomical and clinical prognostic systems.
Until 2000, prior to the combination of the FIGO and WHO classifications, there was no worldwide consensus on the optimal classification system, largely due to a lack of high quality data proving the merit of one system over another. Remarkably, a validated, prospectively tested classification system is yet to be conducted.
Over time, increasing criticisms have emerged regarding the currently adopted combined FIGO/WHO classification system, and its ability to identify patients most likely to develop primary chemotherapy resistance or disease relapse. This is particularly pertinent for patients with low-risk disease, whereby one in three patients are resistant to first line therapy, rising to four out of five women who score 5 or 6.
This review aims to examine the historical basis of the GTN classification systems and critically appraise the evidence on which they were based. This culminates in a critique of the current FIGO/WHO prognostic system and discussion surrounding clinical preference versus evidence based practice.