Cancer is a disease with the highest mortality and morbidity rate worldwide. First-line drugs induce several side effects that drastically reduce the quality of life of people with this disease. Finding molecules to prevent it or generate less aggressiveness or no side effects is significant to counteract this problem. Therefore, this work searched for bioactive compounds of marine macroalgae as an alternative treatment. An 80% ethanol extract of driedCaulerpa sertularioides(CSE) was analyzed by HPLS-MS to identify the chemical components. CSE was utilized through a comparative 2D versus 3D culture model. Cisplatin (Cis) was used as a standard drug. The effects on cell viability, apoptosis, cell cycle, and tumor invasion were evaluated. The IC50of CSE for the 2D model was 80.28 μg/mL versus 530 μg/mL for the 3D model after 24 h of treatment exposure. These results confirmed that the 3D model is more resistant to treatments and complex than the 2D model. CSE generated a loss of mitochondrial membrane potential, induced apoptosis by extrinsic and intrinsic pathways, upregulated caspases-3 and -7, and significantly decreased tumor invasion of a 3D SKLU-1 lung adenocarcinoma cell line. CSE generates biochemical and morphological changes in the plasma membrane and causes cell cycle arrest at the S and G2/M phases. These findings conclude thatC. sertularioidesis a potential candidate for alternative treatment against lung cancer. This work reinforced the use of complex models for drug screening and suggested using CSE’s primary component, caulerpin, to determine its effect and mechanism of action on SKLU-1 in the future. A multi-approach with molecular and histological analysis and combination with first-line drugs must be included.