Date of Award
Medical Doctor (MD)
Francis Y. Lee
Background: Pathological fractures of the femoral shaft are devastating complications of metastatic breast cancer that afflict a myriad of women worldwide. Those affected suffer from debilitating pain, loss of function, and diminished quality of life. Intramedullary nailing with locking screw fixation provides the foundation of femoral fracture repair. However, cancer-induced changes within the local osseous environment drastically impair normal bone healing, leading to nonunion, reduced quality of life, and delays in medical oncologic care. At this time, comparatively little is known about the underlying mechanisms involved in impaired pathological fracture healing. A more thorough understanding of the influence breast cancer metastases have on fracture repair is crucial to improving patient outcomes.Purpose: To develop a murine model mimicking the callus microenvironment present within femoral pathological fractures secondary to breast cancer, to characterize pathological fracture healing, and to establish a targeted therapy that promotes healing of pathological fractures through inhibition of the deleterious effects of metastatic disease. Methods: Femoral midshaft osteotomies were induced in either BALB/cJ or BALB/c nude mice. After internal fixation with a non-locking intramedullary nail, mice were inoculated with breast cancer cell lines, including 4T1, MDA231, HCT1806, and MCF7 (5 x 105 cells). After surgery, mice were monitored throughout the postoperative period and sacrificed at intervals ranging from 4- to 49-days post-surgery. Radiography, x-ray microtomography, histology, immunohistochemistry, and transcriptomic analyses were employed to characterize the osseous microenvironment present throughout different stages of pathological fracture healing. The effects of suppression of MEK/ERK signaling were evaluated using genetic knockouts and pharmacologic supplementation with the MEK inhibitor, trametinib (1 mg/kg). Results: We first devised and optimized a murine xenograft model mimicking the callus microenvironment present in a breast cancer-induced pathological fracture of the femoral shaft. Mice bearing breast cancer xenograft exhibited diminished fracture healing universally compared to mice undergoing fracture healing under normal conditions. Transcriptomic analyses revealed that metastases induce a pro-inflammatory microenvironment and alter the balance between bone deposition and resorption. Suppression of MEK/ERK improved osseous healing, delayed tumor progression, and restored normal transcription patterns. Conclusion: Our study provides the first attempt to define the molecular mechanisms through which breast cancer disrupts healing of pathological fractures in vivo. We created a novel technique whereby the influence of local metastases on fracture healing may be observed. Our results illustrate that a localized inflammatory state contributes to impaired fracture healing and that suppression of the MEK/ERK axis may improve fracture healing and reduced tumor burden. Together, these results may contribute to improved outcomes and clinical prognosis for those afflicted with metastatic breast cancer.
Dussik, Christopher, "Fracture Callus Evaluation In The Setting Of Breast Cancer Metastasis And Rescue Of Healing Via Inhibition Of Erk1/2" (2022). Yale Medicine Thesis Digital Library. 4066.