Supplementary Material for: Inflammatory breast cancer and transient complete radiographic response to chemoimmunotherapy: A Case Report

Introduction
Inflammatory breast cancer is a rare and aggressive subtype, with high breast cancer mortality. Compared to non-inflammatory breast cancer, even after treatment and response to standard of care breast cancer chemotherapy, it has a high propensity for lymph node involvement, high rates of distant metastasis, and shorter survival.
The immune checkpoint inhibitor, Pembrolizumab in combination with chemotherapy is now approved for early triple negative breast cancer and for advanced disease if positive for the programmed cell death ligand 1 protein (PD-L1).
The response and survival of metastatic inflammatory triple negative breast cancer (TNBC) to immunotherapy is largely unreported and we present a case of a young woman with metastatic triple negative inflammatory breast cancer, treated with pembrolizumab, carboplatin, and paclitaxel.

Case Presentation
A 46-year-old female presented with de novo metastatic inflammatory triple negative breast cancer with metastasis to lymph nodes, lung, and bones. She was treated with pembrolizumab, carboplatin, and paclitaxel leading to rapid and complete radiographic response. The response was however short lived, and the patient presented with diffuse disease progression in the lungs with pleural effusions, causing death from respiratory distress.

Conclusion
Treatment for metastatic triple negative inflammatory breast cancer mirrors treatment of metastatic TNBC. In PD-L1 positive disease, treatment with chemotherapy and pembrolizumab is first line and in this case led to robust but short-lived response. Inflammatory breast cancer remains a poorly understood breast cancer subtype, and even in the presence of good treatment response, prognosis and survival remain poor. Further studies are warranted to better understand and treat the disease.