Several parallels may be drawn between pregnancy and cancer. In the course of embryo implantation, trophoblast cells are able to proliferate and invade into maternal tissues, while a complex interaction with the maternal immune system ensures immune tolerance. Similarly, many tumors are able to grow invasively and mask themselves from the immune system. Many of the underlying mechanisms governing embryo implantation and tumor progression seem to lie in close proximity. Among them, the JAK/STAT pathway has been implicated in the transduction of a multitude of signals governing cell differentiation, proliferation, migration and apoptosis. Leukemia Inhibitory Factor (LIF) is a cytokine maximally expressed at the time of implantation that signals through the JAK/STAT pathway. Although its roles have not been completely understood, LIF is assumed to facilitate embryo implantation and regulate tumor invasion through the activity of STAT3. In this sense, this work intended to better clarify the role of LIF and the JAK/STAT pathway in choriocarcinoma cell lines, which are considered models for studying trophoblast physiology. Different choriocarcinoma cell lines have been treated with LIF and IL-6 to investigate the association of these cytokines with the phosphorylation of STAT3. Furthermore, the constitutive expression and phosphorylation of three Janus kinases (JAKs) have been analyzed by means of Western blot. The expression of JAKs has been also verified in human placental tissues by immunocytochemistry. Aiming to silence the expression of JAK1 in choriocarcinoma cell lines, different transfection reagents and siRNA concentrations have been tested for RNA interference. Knock-down efficiency has been evaluated by Western blot. Finally, a set of functional tests has been performed to evaluate if LIF treatment and/or kinase silencing might modify cell behavior. In this sense, flow cytometry has been used to quantify cell proliferation, migration and invasion rates.