Breast Cancer

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TU_11_3427 - Palbociclib Enhances Pulmonary Fibrosis in Patients Undergoing Thoracic Radiation Therapy: A Case Series and Review of the Literature

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Palbociclib Enhances Pulmonary Fibrosis in Patients Undergoing Thoracic Radiation Therapy: A Case Series and Review of the Literature
R. Kalash1, N. A. Iarrobino1, S. Beriwal2, M. Sun3, S. M. Glaser2, and C. E. Champ1; 1Department of Radiation Oncology, Hillman Cancer Center, University of Pittsburgh School of Medicine, Pittsburgh, PA, 2UPMC Hillman Cancer Center, Pittsburgh, PA, 3Department of Medical Oncology, Hillman Cancer Center, University of Pittsburgh School of Medicine, Pittsburgh, PA

Purpose/Objective(s): Palbociclib (Ibrance), is an oral cyclin-dependent kinase (CDK) 4 and 6 inhibitor with a synergistic effect upon tumor cells alongside anti-estrogen compounds. Palbociclib and letrozole is becoming the current standard of care for metastatic estrogen receptor positive (ER+), HER2/neu negative breast cancer due to a large improvement in progression free survival in randomized trials. However, many metastatic breast cancer patients require palliative radiation therapy (RT), leading to the combination of both agents with RT and unknown potential synergistic side effects. In this study, we set out to determine the effect of concurrent palbociclib and radiation therapy on pulmonary toxicity.

Materials/Methods: The medical records and radiation treatment plans of all patients who underwent concurrent palbociclib and radiation therapy for metastatic breast cancer were reviewed from 2016-2017.

Results: Three patients received palbociclib, letrozole, and palliative RT concurrently. Two of three patients received palliative radiation therapy to the lungs, while one patient received chest wall radiation therapy. All patients experienced pronounced pulmonary fibrosis, confirmed on imaging, though radiation dose to the lung was well below typical thresholds. Furthermore, two patients who received palliative radiation therapy for lung metastasis had profound and atypical radiation pneumonitis, refractory to corticosteroid treatment. Symptoms improved after discontinuation of palbociclib.

Conclusion: We caution against the delivery of concurrent palbociclib, letrozole, and radiation therapy overlapping with the lungs. Furthermore, with the rapid introduction of new targeted agents that modulate cell cycle progression and impact radiosensitivity, care must be taken when delivered with radiation therapy. This is the first report of palbociclib, antihormonal therapy, and RT causing pronounced lung toxicity, further large cohort studies are needed to explore this relationship.

Author Disclosure: R. Kalash: None. N.A. Iarrobino: None. S. Beriwal: Consultant; Varian, XOFT. Editor; Red Journal. Editorial Board; Brachytherapy Journal. Senior Editor; iJROBP. M. Sun: None. S.M. Glaser: None. C.E. Champ: None.

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