De-escalation of breast and axillary treatment in breast cancer patients

This thesis focuses on improving breast cancer treatment through response-guided therapies. While the number of breast cancer diagnoses continues to rise, survival rates have improved due to effective screening programs and systemic treatments. The prognosis of breast cancer is highly dependent on tumor stage, biological characteristics, and response to therapy. Neoadjuvant systemic therapy (NST) allows for tumor shrinkage and monitoring of treatment response, providing the opportunity for tailored treatment. The likelihood of achieving a pathological complete response (pCR) varies by subtype, with the highest rates seen in HER2+ and triple-negative (TN) breast cancer. Achieving pCR is associated with better long-term survival and lower recurrence rates and as long-term oncological outcomes improve, it is important to reconsider whether the benefits of locoregional treatment outweigh the associated side effects.
This thesis explores minimally invasive biopsies to evaluate response to NST as imaging methods like MRI and FDG-PET/CT are useful, but not accurate enough to reliably detect pCR. However, small biopsies may miss relevant residual disease, emphasizing the need for breast surgery in many patients. The thesis also examines tailored locoregional treatments, such as omitting radiotherapy in patients achieving pCR and optimizing surgery for invasive lobular carcinoma.
A major focus is on tailored axillary treatment based on NST response in clinically node positive patients. The MARI procedure, involving the removal of a pre-NST marked lymph node during surgery, enables tailored axillary treatment reducing unnecessary axillary lymph node dissections. This approach has shown excellent survival outcomes and low recurrence rates in breast cancer patients with limited and extensive nodal disease.
By investigating innovative diagnostic and treatment strategies, this thesis provides new insights into personalizing breast cancer treatment, minimizing overtreatment, and improving patients' quality of life.