Use of Concurrent Systemic Therapies with Adjuvant Intensity Modulated Proton Beam Therapy (IMPT) in Women with high-risk, locally advanced breast cancers
Faculty and Abstracts
Purpose: Several publications have indicated an increase in skin toxicity with the use of IMPT compared to photon therapy for the treatment of breast cancer. This has led to a general hesitancy to consider concurrent systemic therapy due to concerns for even greater skin toxicities that could have a negative impact on patient outcomes and quality of life. At XXXX we have routinely considered concurrent systemic therapy with IMPT due to our experience in utilizing concurrent therapy with photons. Here we present our initial experience in the use of concurrent systemic therapies with IMPT.
Methodology: Under IRB approval, we retrospectively reviewed 453 definitively treated breast cancer patients from 2016 – 2023 using IMPT as part of their cancer care. This analysis includes patients receiving concurrent systemic therapy (excluding hormonal therapy blockade only) with at least 1 year of follow up. Patients were treated with surgery and systemic therapies as per standards of care. Radiation therapy was administered using pencil beam scanning IMPT with daily image guidance and patients were prescribed a minimum of 50 Gy up to 70.2 Gy for gross residual disease. Acute toxicities were graded by CTCAE v4.03 criteria. Descriptive statistics were used to evaluate a variety of parameters including toxicity analysis and treatment breaks.
Results: 79 patients received concurrent systemic therapy during this time period with a median follow up of 30.5 months. Average patient age was 53 (range: 28-77). 19 patients received re-irradiation; 11 patients were treated for recurrent breast disease. 24 patients were triple negative and 53 were her2 positive by IHC or FISH. 53 patients received concurrent her2 directed therapy including trastuzumab alone, trastuzumab/pertuzumab, pertuzumab/trastuzumab/hyaluronidase-zzxf (Phesgo) and TDM-1. 19 patients received concurrent capcitabine, four patients received concurrent pembrolizumab and three patients received a concurrent CDK4/6 kinase inhibitor. 8 patients (10%) required a recommended or self-directed treatment break due to side effects with an average break of 4.6 days. Acute toxicities were reported on a weekly basis during treatment. There were 137 grade 1 toxicities including radiation dermatitis, anorexia, breast pain, hyperpigmentation, weight loss, fibrosis and GI related (nausea/esophagitis/dysphagia); 51 grade 2 toxicities (46 radiation dermatitis/hyperpigmentation and 4 breast pain) and 4 grade 3 toxicities (3 radiation dermatitis and 1 breast pain).
Conclusions: In this high risk group of patients, concurrent systemic therapy while receiving IMPT to the chest/breast and/or draining lymph nodes was well tolerated with a low incidence of treatment breaks. For patients in whom concurrent systemic therapy is indicated, receipt of IMPT should not be a barrier to this therapy. Patients should continue to undergo close monitoring during receipt of treatment with engagement of the multi-disciplinary team, however this approach appears safe and can be considered in the appropriate patient population.
