A Case Report of a Breast Cancer Patient Developing Pneumonitis as a Result of Abemaciclib Therapy

Abstract

Introduction: Breast cancer is the most common cancer affecting women in the United States, and the prognosis is good, with a 5-year survival rate of 91.2%. Advancements in treatment options using molecular profiling have allowed therapies to be more personalized and have improved patient outcomes. Of the many specific therapy agents, cyclin-dependent kinase (CDK) 4/6 inhibitors, such as abemaciclib, are commonly used. Case: We present a case of a 74-year-old female with a history of HR+ breast cancer who has been on abemaciclib for over two and a half years and developed pneumonitis. Discussion: Pneumonitis, as a direct result of abemaciclib or other CDK 4/6 inhibitors, is a rare side effect with an unknown mechanism of action. The Federal Drug Administration (FDA) has warned about the potential for this severe and potentially fatal inflammation of the lungs when using these agents. No studies have investigated additional risk factors in developing this side effect. However, reviewing other case reports supports that patients typically develop this side effect within the first three years of treatment initiation. The mechanism of manifesting this side effect has not been explored. However, it has been proposed that it is related to over activation of the immune system. Treatment includes clinical observation for asymptomatic and glucocorticoids for symptomatic patients. Conclusion: This case highlights the complexities of breast cancer therapies and the rare side effects of pneumonitis with CDK 4/6 inhibition from drugs like abemaciclib. More research should be conducted to better understand and prevent the manifestation of this potentially fatal side effect.