Lung adenocarcinoma is the most common form of lung cancer with a 5-year survival rate of 15%, largely due to asymptomatic metastasis and late diagnosis. Overexpression of Polycomb group (PcG) proteins, particularly EZH2, the catalytic component of Polycomb Repressive Complex 2 (PRC2), has been associated with the pathogenesis of lung cancer, frequently showing correlation with cancer progression and poor prognosis. In this study, EZH2 levels were modulated by CRISPR/Cas9 gene editing and PRC2 activity was inhibited with EZH2 inhibitor EPZ6438 or EED inhibitor MAK683. EZH2 gene editing reduced cell proliferation, migration, invasion, and colony formation and reduced NFκ-B signaling activation, indicating an antitumoral effect in vitro. Moreover, EZH2 inhibition also increased the expression of differentiation-related genes, such as GATA5, FOXA2, and lung surfactants, indicating a pro-differentiation effect. However, EZH2-edited cells injected into an immunocompromised mouse model generated larger tumors compared to unedited cells. This was accompanied by increased expression of other PcG genes, including EZH1, CBX2, RING1, EED, and SUZ12, suggesting a compensatory interaction between PRC2 and PRC1 complexes. These findings provide significant clinical relevance, both in elucidating the mechanisms of novel molecular targets and in guiding treatment strategies for lung cancer when using epigenetic inhibitors.