The chorioallantoic membrane (CAM) model, generated during avian development, can be used in cancer research as an alternative in vivo model to perform tumorigenesis in ovo due to advantages such as simplicity, low cost, rapid growth, and being naturally immunodeficient. The aim of this systematic review has been to compile and analyze all studies that use the CAM assay as a tumor induction model. For that, a systematic search was carried out in four different databases: PubMed, Scopus, Cochrane, and WOS. After eliminating duplicates and following the established inclusion and exclusion criteria, a total of 74 articles were included. Of these, 62% use the in ovo technique, 13% use the ex ovo technique, 9% study the formation of metastasis, and 16% induce tumors from patient biopsies. Regarding the methodology followed, the main species used is chicken (95%), although some studies use quail eggs (4%), and one article uses ostrich eggs. Therefore, the CAM assay is a revolutionary technique that allows a simple and effective way to induce tumors, test the effectiveness of treatments, carry out metastasis studies, perform biopsy grafts of patients, and carry out personalized medicine. However, unification of the methodology used is necessary.

Background: Lung cancer is a leading cause of cancer-related deaths worldwide. Its high incidence and poor prognosis demonstrate the need to investigate new therapies. The PI3K/AKT pathway is activated in carcinogenic processes such as invasion, proliferation, and drug resistance. MiR-21 is a microRNA overexpressed in numerous types of cancer and which activates PI3K/AKT pathway by down-regulating its main targets, PTEN and PDCD4. CRISPR is a revolutionary gene-editing technology that allows genes to be deleted. The aim of this study was to use CRISPR/Cas9 technology as an option to reduce carcinogenic and drug resistance processes by eliminating miR-21. Methods: CRISPR/Cas9 was used to knock out miR-21 (miR-21 KO) in A549 lung cancer cells and thus reverse the carcinogenic processes activated by miR-21 overexpression. Furthermore, the effect of miR-21 KO on drug resistance was studied, choosing the main chemotherapeutic agents used for the treatment of lung cancer: gemcitabine, carboplatin, paclitaxel, and oxaliplatin. Results: miR-21 KO A549 cells exhibited a reduction in proliferation, migration, and colony formation compared to A549 cells. In contrast, the expression of PTEN and PDCD4 increased in miR-21 KO A549 cells. Furthermore, miR-21 KO A549 cells showed a decrease in the IC₅₀ of the drugs used for the treatment of lung cancer: gemcitabine, carboplatin, paclitaxel, and oxaliplatin. Conclusions: Based on these results, miR-21 knock-out using CRISPR/Cas could be a promising strategy for the treatment of lung cancer.