Several factors contribute to the importance of GAS5 in breast cancer research: (i) GAS5 downregulation is associated with an unfavorable clinical outcome of BC patients; (ii) altered GAS5 levels have been detected following anti-cancer therapies, including chemotherapy and radiotherapy; and (iii) GAS5 plays a role in sensitizing cancer cells to different types of treatment, promoting apoptosis, and in inhibiting the proliferation of cancer cells. This evidence concerns the gene GAS5 and cancer.