Abstract Introduction The evolution of breast cancer treatment has seen a paradigm shift with the incorporation of CDK4/6 inhibitors leading to significantly improved outcomes in both the metastatic and high-risk adjuvant settings. However, their efficacy is tempered by the risk of off-target toxicities, including the potentially severe and rare complication of drug-induced pneumonitis or Interstitial Lung Disease (ILD), necessitating heightened clinical surveillance. This report details a catastrophic clinical course of presumed Abemaciclib-induced pneumonitis, emphasizing the rapid progression and high mortality risk. Case Report A 57-year-old female with a history of ER+/PR-/HER2- invasive ductal carcinoma status post bilateral mastectomy, was undergoing a two-year regimen of adjuvant Abemaciclib and an aromatase inhibitor. She presented acutely with a one-week history of rapidly worsening dyspnea and a dry, intractable cough. She exhibited acute hypoxic respiratory failure, requiring immediate high-flow nasal cannula support. Initial management involved empirical broad-spectrum antibiotics, antifungal agents, and high-dose intravenous corticosteroids. Crucially, Abemaciclib was immediately held due to strong suspicion of drug-induced lung injury (DILI). Radiographic studies revealed concerning progression: A CT chest two months prior had documented subtle ground-glass opacities (GGOs) and reticular interstitial changes, confirmed by lung biopsy as interstitial fibrosis and bronchiolar metaplasia (negative for malignancy). A repeat CT thorax performed just prior to admission showed marked progression with extensive bilateral consolidation (Image-left)). Despite aggressive supportive care, her respiratory status deteriorated precipitously, requiring mechanical ventilation within 24 hours. A comprehensive workup, including bronchoalveolar lavage (BAL) and respiratory viral panel failed to isolate any infectious or neoplastic etiology, strongly supporting the diagnosis of DILI. The infiltrates proved refractory to maximal ventilatory and medical support (Image-left). Given the irreversible, fulminant course of presumed Abemaciclib-induced ILD, the family opted to withdraw life support, and the patient expired on day 5 of hospitalization. Discussion This case reveals a critical need for enhanced clinical practice. This tragic, fulminant course from subclinical interstitial changes to fatal acute respiratory distress within days serves as a stark warning about Abemaciclib-associated pneumonitis. Clinicians must recognize that despite its rarity, this complication carries a high mortality risk, necessitating a low threshold for intervention; specifically, any new or worsening respiratory symptom in a patient on Abemaciclib demands immediate drug cessation, rapid exclusion of infectious etiologies, and the prompt initiation of high-dose systemic glucocorticoids. Furthermore, the existence of subtle, pre-existing radiographic findings emphasizes the vital importance of proactive, longitudinal pulmonary surveillance. This abstract is funded by: None
Guiseppi et al. (Fri,) studied this question.