A research team from the University of Delhi, South Campus, and Tata Memorial Hospital in Mumbai has discovered that the CDKN1B gene plays a crucial role in the resistance of hormone receptor-positive (HR+) breast cancer to standard hormone therapies. This type of breast cancer represents nearly 70% of all cases in India, yet about 40% of patients develop resistance to treatments like tamoxifen within months to a few years. The study, led by Amit Dutt and Sudeep Gupta, found that mutations or loss of the CDKN1B gene hinder the production of the p27 protein, which is essential for the effectiveness of these therapies. By analyzing 186 breast cancer patients, the researchers noted that those who developed resistance had significant alterations in the CDKN1B gene. Importantly, restoring this gene's function allowed the drug to regain its effectiveness. Additionally, they found that CDK4/6 inhibitors, such as palbociclib, remain effective even without p27. Their research suggests that combining tamoxifen with CDK4/6 inhibitors could enhance treatment outcomes. This discovery offers a new biomarker for identifying patients at risk of resistance, allowing for earlier intervention with alternative therapies, potentially improving survival rates for many women in India, where approximately 200,000 new breast cancer cases are reported annually.