Gestational trophoblastic diseases are interrelated conditions characterized by abnormal growth of chorionic tissues with varying propensitiesfor local invasion and metastases. These diseases are characterized by altered expression of several growth regulatory factors and oncogenes. On the basis of the expression of various oncogenes and growth factors, partial mole appears to be more like normal placenta, while complete mole seems to be more like choriocarcinoma. These results may have both prognostic and therapeutic consequences and provide insight into the relationship between normal placenta and gestational trophoblastic diseases.