Deregulation of the cyclin D‐CDK4/6‐INK4‐RB pathway leading to uncontrolled cell proliferation, is frequently observed in breast cancer. Currently, three selective CDK4/6 inhibitors have been FDA approved: palbociclib, ribociclib and abemaciclib. Despite promising clinical outcomes, intrinsic or acquired resistance to CDK4/6 inhibitors has limited the success of these treatments; therefore, the development of various strategies to overcome this resistance is of great importance. We highlight the various mechanisms that are directly or indirectly responsible for resistance to CDK4/6 inhibitors, categorizing them into two broad groups; cell cycle‐specific mechanisms and cell cycle‐nonspecific mechanisms. Elucidation of the diverse mechanisms through which resistance to CDK4/6 inhibitors occurs, may aid in the design of novel therapeutic strategies to improve patient outcomes. This review summarizes the currently available knowledge regarding mechanisms of resistance to CDK4/6 inhibitors, and possible therapeutic strategies that may overcome this resistance as well.

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Immune checkpoint blockade is promising for treating non-small-cell lung cancer (NSCLC). We used multipanel markers to predict the response to immune checkpoint inhibitors (ICIs) by characterizing gene expression signatures or individual genes in patients who showed durable clinical benefit to ICIs. Twenty-one patients with NSCLC treated with single-agent anti-programmed cell death protein (PD)-1 antibody were analyzed and their clinicopathological characteristics and response to ICIs were characterized. Nine (43%) showed a durable clinical benefit (DCB), while the remaining 12 (57%) patients showed non-durable benefit (NDB). The M1 and peripheral T cell signatures showed the best performance for discriminating DCB from NDB (sensitivity, specificity, accuracy = 0.89, 1.0, 0.95, respectively). Progression-free survival (PFS) was significantly longer in patients with high M1 signature or high peripheral T cell signature scores. CD137 and PSMB9 mRNA expression was higher in the DCB group than in the NDB group. Patients with high PSMB9 expression showed longer PFS. M1 signature, peripheral T cell signature and high mRNA expression level of CD137 and PSMB9 showed better predictive performance than known biomarkers, such as PD-L1 immunohistochemistry, tumor mutation burden, or tumor-infiltrating lymphocytes.