Long non-coding RNA (lncRNA)-maternally expressed gene 3 (MEG3) and microRNA-21 (miR-21) have been widely recognized as tumor suppressor and promoter. The competing endogenous RNA (ceRNA) hypothesis provides a new strategy for studying the interaction of RNAs. In recent years, studies have shown that MEG3 can play an important role in the occurrence, development, proliferation, metastasis, drug resistance and prognosis of breast cancer, cervical cancer, gastric cancer, lung cancer, leukemia and other malignant tumors as the ceRNA of miR-21.