ESTRO 2024 - Abstract Book

S633

Clinical - Breast

ESTRO 2024

secondary lung lesions, hepatic and brain. Thirty-two (67%) patients had CDK4i-related grade 1 hematological toxicity before RTE. During RTE, hematological toxicity was manifested in 3 cases (6.25%) (1 patient with grade 3 toxicity). Regarding non-hematological toxicity, during RTE, 4 patients (8.33%) manifested grade 2 radiodermatitis (2nd week) and 2 patients (4.17%) developed grade 3 radiodermatitis for which RTE and CDK4/6i (Abemaciclib) treatments were interrupted. After RTE, 4 patients (8.33%) and 3 patients (6.25%), respective had grade 2 neutropenia and respective grade 3 neutropenia following pleural and sternum secondary lesions. Regarding non hematological toxicity, 2 patients (4.17%) developed grade 3 enteritis at 1 or 2 weeks after pelvic bones metastases’ irradiation (in field toxicity). Evaluating the dose at bowel bag, the value (29.5Gy) falls well below the normal bowel radiation tolerance dose (45-50 Gy). One patient had 4 grade leukopenia and 4 grade thrombocytopenia at 1 week after RTE ending for pelvic bones for which the CDK4/6i dosage decreasing was needed. The results are difficult to interpret, in clinical practice, due to the different RTE fractionation schedules and various time points of CDK4/6i. The dosimetric parameters analyzed were maximum dose of bowel bag, the percentage of bowel bag volume receiving ≥ 35Gy (V35) and the bowel bag volume receiving 45Gy (V45). Given the variations in the fractionation schemes, the prescribed physical dose was converted into a biologically effective dose (BED) and an equivalent dose of 2 Gy per fraction (EQD2). The moderate or greater enterocolitis group was non-significantly associated with higher bowel bag EQD2.

Conclusion:

Radiotherapy was well tolerated for most patients treated with CDK4/6. High-grade hematological toxicities are common but rarely influence the treatment course. Radiotherapy seems not to bring additionally myelosuppression for treatment. However, the toxicities are higher in sequential vs. concomitant treatments.

Keywords: radiotherapy, CDK4/6i, toxicities

References:

Franco, R.; Cao, J.Q.; Yassa, M.; Hijal, T. Safety of CDK4/6 Inhibitors Combined with Radiotherapy in Patients with Metastatic Breast Cancer: A Review of the Literature. Curr. Oncol. 2023, 30, 5485 – 5496. https://doi.org/ 10.3390/curroncol30060415.

2236

Digital Poster

Locoregional Recurrence in Adenoid Cystic Carcinoma of Breast: A Retrospective, Multicenter Study

Sang Min Lee 1 , Bum-Sup Jang 1 , Won Park 2 , Yong Bae Kim 3 , Jin Ho Song 4 , Jin Hee Kim 5 , Tae Hyun Kim 6 , In Ah Kim 7 , Jong Hoon Lee 8 , Sung-Ja Ahn 9 , Kyubo Kim 10 , Ah Ram Chang 11 , Jeanny Kwon 12 , Hae Jin Park 13 , Kyung Hwan Shin 1 1 Seoul National University Hospital, Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea, Republic of. 2 Samsung Medical Center, Sungkyunkwan University School of Medicine, Radiation Oncology, Seoul, Korea, Republic of. 3 Yonsei Cancer Center, Yonsei University College of Medicine, Radiation Oncology, Seoul, Korea, Republic of. 4 Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Radiation Oncology, Seoul, Korea, Republic of. 5 Dongsan Medical Center, Keimyung University School of Medicine, Radiation Oncology,