Nowadays, molecular research is essential for the better understanding of tumor cells’ pathophysiology. The increasing number of neoplasms is taken under ‘the molecular magnifying glass’; therefore, it is possible to discover the complex relationships between cytophysiology and tumor cells. Signal transducer and activator of transcription 3 (STAT3) belongs to the family of latent cytoplasmic transcription factors called STATs, which comprises seven members: STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B, and STAT6. Those proteins play important role in cytokine-activated gene expression by transducing signals from the cell membrane to the nucleus. Abnormal prolonged activation results in tumorigenesis, metastasis, cell proliferation, invasion, migration, and angiogenesis. Inhibition of this transcription factor inhibits the previously mentioned effects in cancer cells, whereas normal cells are not affected. Hence, STAT3 might be a viable target for cancer therapy.