CONCURRENT USE OF ABEMACICLIB AND RADIOTHERAPY IN METASTATIC BREAST CANCER PATIENTS: A SINGLE CENTRE EXPERIENCE.

INTRODUCTION: There is little evidence regarding the safety and efficacy of the combination of abemaciclib plus radiotherapy (RT). The majority of studies investigated the combination of RT with Palbociclib or Ribociclib reporting that hematological toxicity is common. Given the unique toxicity profile of Abemaciclib with greater gastrointestinal toxicity compared to hematological toxicity, we wanted to evaluate the toxicity of the combination with RT in metastatic breast cancer (BC) patients. METHODS: Patients with histologically proven metastatic or locally advanced BC treated with RT and concurrent Abemaciclib were selected. Toxicity was assessed according to the NCI-CTCAE V4.0. RESULTS: 32 metastatic sites were treated in nineteen patients and analyzed. All patients received Abemaciclib during the RT course. 68% of patients received a full dose of Abemaciclib during RT. 71.9% of patients received a palliative intent (median dose= 30Gy, range= 8-30Gy), 26.3% were treated to 9 oligo-metastatic or oligo-progressive sites of disease with stereotactic body radiotherapy (SBRT) (median dose = 30Gy, range 21-30Gy given in 3-5 fractions Overall the rate of G3 toxicity was 15.7%. The rate of G3 hematological toxicity was 10.6 % (2/19 patients, one G3 neutropenia and one G3 anemia). No patient presented diarrhea, including those treated to RT sites close to the bowel. One patient developed G3 skin toxicity. Pain significantly improved after RT (mean value NRS pre-RT=3.9, SD=3.07; mean value NRS after-RT=0.9, SD= 0.46; p=<0.0001) Conclusion: Abemaciclib and Concomitant RT seem well tolerated showing acceptable toxicity.

Breast Volume Is a Predictor of Higher Heart Dose in Whole-Breast Supine Free-Breathing Volumetric-Modulated Arc Therapy Planning.

In breast cancer volumetric-modulated arc therapy (VMAT) planning, the rotation of the gantry around the target implies a greater dose spreading to the whole heart, compared to tangential-field standard treatment. A consecutive cohort of 121 breast cancer patients treated with the VMAT technique was investigated. The correlation of breast volume, heart volume and lung volume with mean heart dose (mHD) and mean and maximum LAD dose (mLAD dose, MLAD dose) was tested, and a subsequent a linear regression analysis was carried out. VMAT treatment plans from 56 left breast cancer and 65 right breast cancer patients were analyzed. For right-sided patients, breast volume was significantly correlated with mHD, mLAD and MLAD dose, while for left-sided patients, breast volume was significantly correlated with mHD and mLAD, while heart volume and lung volume were correlated with mHD, mLAD and MLAD dose. Breast volume was the only predictor of increased heart and LAD dose (p ≤ 0.001) for right-sided patients. In left-sided patients, heart and lung were also predictors of increased mHD (p = 0.005, p ≤ 0.001) and mean LAD dose (p = 0.009, p ≤ 0.001). In this study, we observed an increase in heart and LAD doses in larger-breasted patients treated with VMAT planning. In right-sided patients, breast volume was shown to be the only predictor of increased heart dose and LAD dose.

BOMB trial: First results of stereotactic radiotherapy to primary breast tumor in metastatic breast cancer patients.

Aim: A prospective dose escalation trial was developed to evaluate the maximum tolerated dose of stereotactic body radiotherapy (SABRT) to primary breast cancer in stage IV disease. The aim of the present report was to describe safety and outcome of the first dose level cohort of patients. Material and methods: Patients with histologically confirmed diagnosis of invasive breast carcinoma (biological immuno-histochemical profile: luminal and/or HER2 positive) and distant metastatic disease not progressing after 6 months of systemic therapy with a tumor CT or 5FDG-PET detectable were deemed eligible. The starting dose was 40 Gy in 5 fractions (level 1) because this dose proved to be safe in previous dose-escalation trial on adjuvant stereotactic body radiotherapy. The maximum dose level was chosen as 45 Gy in 5 fractions. Dose limiting toxicity was any grade 3 or worse toxicity according to CTCAE v.4. Time-to-event Keyboard (TITE-Keyboard) design (Lin and Yuan, Biostatistics 2019) was used to find the maximum tolerated dose (MTD). MTD was the dose of radiotherapy associated with a ≤ 20% rate pre-specified treatment-related dose-limiting toxicity (DLT). Results: To date 10 patients have been treated at the starting dose level. Median age was 80 years (range 50-89). 7 patients had a luminal disease, while 3 patients had an HER2 positive disease. No patient suspended ongoing systemic treatment. No protocol defined DLTs were observed. Grade 2 skin toxicity occurred in 4 patients with diseases located close to or involving the skin. Median follow-up was 13 months and all 10 patients were evaluable for response: 5 achieved a complete response, 3 achieved a partial response and 2 showed a stable disease, all with a clinical benefit (resolution of skin retraction, bleeding and pain). The mean reduction in the sum of the largest diameters of target lesions was of 61.4% (DS=17.0%). Conclusions: SABR to primary breast cancer seems feasible and is associated with symptoms reduction. Continued accrual to this study is needed to confirm the safety and assess the MTD. Clinical trial registration: ClinicalTrials.gov, identifier NCT05229575.