A major challenge in tumor therapy is the decrease or even the halting of cell proliferation and migration of cancerous cells. In the present study, we have analyzed the impact of a pharmacological blockade of the PI3K/Akt and MAPK/ERK1/2 signaling pathways on cell migration, proliferation and cell death in three human thyroid tumor cell lines that represent the main types of malignant thyroid carcinomas (B-CPAP, follicular; Cal-62, anaplastic; FTC-133, papillary thyroid carcinoma cells) and in which these pathways are constitutively activated. In general, pharmacological perturbation of PI3/Akt (application of MK-2206) and MEK/ERK1/2 (application of PD0325901 or U0126) signaling led to a cell line and drug-specific decrease in the proliferation and migration potential of thyroid carcinoma cells, although to a varying extent. However, one exception became apparent: in Cal-62 cells inhibition of the MEK/ERK1/2 module increased the migration rate up to 50%. This effect could be prevented by a simultaneous suppression of the PI3/Akt pathway, but also by application of the multiple kinase inhibitor sorafenib, a treatment that did not change the activation state of Akt. Thus, a pharmacological perturbation of canonical signaling pathways in thyroid carcinoma may induce drug-dependent yin-yang effects that are characterized by a simultaneous suppression of one (i.e., proliferation) and the activation of another (i.e., migration) cellular process. The appearance of such phenomena should be taken into account when therapy plans are established.