Objective: To establish the role of Placental Site Trophoblastic Tumour (PSTT) and so called Epitheloid Trophoblastic Tumour (ETT) among malignant trophoblastic tumours (MTT). Design of the study: Retrospective analysis. Setting: Trophoblastic Disease Centre (TDC-CZ) in the Czech Rep., Institute of Mother and Child Care (UPMD), Prague 4. Methods: Clinical pathologic analysis of 367 malignant trophoblastic tumours (MTT) was perfor- med during the years 1955 to 2000. All cases were diagnosed, evaluated and treated in the TDC- CZ in the Czech Rep. Results: Based on the comparison of development stages of orthologic trophoblast 5 types of MTT were introduced: 1. typical „classical“ choriocarcinoma (CH), so called No Special Type (CH- NST), 2. CH-syntiotrophoblastic (CH-SYN), 3. CH-cytotrophoblastic (CH-CYT), 4. CH-dissociated (CH-DIS), 5. Ch-undifferentiated (CH-UND). Malignant types of PSTT are morphologically identical with CH-CYT and CH-DIS, ETT correlates with CH-UND. The occurrence of all types of CH is presented in relation to different treatment strategy in three periods of time: 1. period (1955-1963) without chemotherapy (CHT), 2. period (1964-1980) undifferentiated CHT, 3. period (1981-2000) differentiated chemotherapy - treatment protocols. During the whole period CH-NST was detected 294x, and represented 80,1% of all MTT. CH-SYN was diagnosed 14x i.e. 3,8%, CH-CYT in 12 cases, i.e. 3,3%, CH-DIS in 22 cases, i.e. 6% and CH-UND was diagnosed 25x, i.e. 6,8%. During all three periods the number of MTT was nearly the same but the mortality has changed dramatically. In the first period mortality presented 94,5% in all types, in the second period mortality dropped to 43,6% and in the third period to 5,8%. Significant differences in mortality were due to histological type. In CH-NST mortality represented only 3,2% and in highly differenti- ated type CH-SYN it was 0%. On the other hand mortality in poorly differentiated types repre- sented in CH-CYT 40%, in CH-UND 18,1%, in CH-DIS 11,1%. Lethality of PSTT comprises the mortality of CH-CYT and CH-DIS together and in the first period represented 100%, in the second period it dropper to 53,8% and in the third period to 21,4%. Mortality on ETT correlating to CH-UND comprised in the first period 100%, in the second period 44,4% and in the third period 18,1%.-due to aggressive polychemotherapy and early surgical intervention. Conclusion: Presented morphologic characteristic makes routine bioptic diagnosis of malignant types of PSTT and ETT possible as well as their differentiation from benign trophoblastic lesion. These tumours - PSTT and ETT-belong to poorly differentiated MTT.

        Key words: Placental Site Trophoblastic Tumour, Epitheloid Trophoblastic Tumour, mortality on