ESTRO 2023 - Abstract Book

S998

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ESTRO 2023

median follow-up of 34 months, 117 (42%) patients completed the q-DASH questionnaire. The mean q-DASH score was 20.8 ranging between 8.9 and 27.6. The mean q-DASH score tended to be lower in patients treated with lumpectomy when compared to patients treated with mastectomy at 17.3 vs 19.6, p=0.08. The V30 Gy to the shoulder was statistically related to higher q-DASH scores, thus to higher shoulder morbidity, with Pearson coefficient of 0.37, p=0.042. No other statistical association was found between dosimetric parameters to the shoulder and patient reported late toxicity. Conclusion We found that 3D conformal breast cancer radiotherapy with RNI results in long-term shoulder morbidity, which was statistically related to the volume of the shoulder receiving 30 Gy. These results need to be prospectively confirmed with consistent baseline and post treatment assessment (pre and post-surgery/radiotherapy) to better understand the real impact of radiotherapy on shoulder morbidity. 1 INT IRCCS Fondazione Pascale, Radioterapy, Naples, Italy; 2 INT IRCCS Fondazione Pascale, Radiotherapy, Naples, Italy; 3 INT IRCCS Fondazione Pascale, Raditherapy, Naples, Italy Purpose or Objective Cyclin-dependent kinase (CDK) 4/6 inhibitors are utilized in the setting of advanced, hormone receptor (HR+) positive breast cancer. A potential synergy between radiation therapy (RT) and CDK4/6 inhibitors (CDKi) emerged from preclincial data. We assessed clinical outcomes of patients treated at our institution with the use of CDKi and stereotactic radiation (SRT) in the management of HR+ breast brain metastases Materials and Methods We conducted a retrospective analysis of patients who received stereotactic radiotherapy for HR+ brain metastases within 6 months of CDKi administration. The primary endpoint was neurotoxicity during or after stereotactic radiation. Secondary endpoints were local control, brain control, distant control. Results It was evaluated a total of 24 lesions treated with stereotactic radiation in 10 patients. Four patients received palbociclib (40%) and 6 patients ribociclib (60%). RT was delivered concurrently in 7 lesions (30%) and sequential in17 lesions (70%). Median follow-up following stereotactic radiation was 11 months. One lesion (4%) developed radionecrosis without clincal symptoms. None patients developed acute severe toxicity. At 6 month 80% of patients presented brain control an 90% of patients distal control. At 12 month 30% of patients presented brain and distal control. None patients developed relapse in the treatment site. Conclusion Stereotactic radiation to breast brain metastases was well tolerated alongside CDK4/6 inhibitors. Compared to historical data, brain metastases control rates are similar. Purpose or Objective Cyclin-dependent kinase (CDK)4/6 inhibitors are utilized in locally advanced or as first-line therapy for metastatic hormone receptor positive breast cancer. However, there are limited data on safety of combined radiotherapy (RT) and CDK4/ 6 inhibition. Materials and Methods We conducted a multicentric retrospective study of women with breast cancer who received palliative RT or adiuvant RT within 15 days of CDK4/6 inhibitor use. The primary endpoint was toxicity per Common Terminology Criteria for Adverse Events v5. Results Fourty-one patients received therapy with CDK inhibitor: 22 with ribocilcib (54%), 17 with palbociclib (41%) and 2 with abemaciclib (5%). These patients underwent 50 courses of radiotherapy. Among RT treatment (50) 11 patients (22%) received radiotherapy on breast/chestwall with an adjuvant intent with a median dose of 50 Gy in 25 fractions. The Median RT dose for the metastatic site was 30Gy. Treated sites included brain (n=10, 20%), spine (n=14, 28%), other bony sites (n=13, 26%) and others (n=2, 4%). Metastatic sites were treated with 3D technique in 21 cases and with SRS/SRT in the other 18 cases. RT was delivered concurrently or sequential CDK4/6 inhibitors in 28 (56%) and 22 (44%) cases respectively. One acute grade 3 hematologic toxicity occurred with interruption of CDKi before the RT course. No increased hematologic toxicity was attributable to RT with no grade 3 hematologic toxicities rates before, during, and 2 weeks after the end of RT Conclusion The use of RT within 2 weeks of CDK4/6 inhibitors had low acceptable toxicity and high efficacy, suggesting that it is safe for palliation of metastatic breast cancer. PO-1246 CDK4/6-I and SRT in the treatment of hormone receptor positive breast cancer brain metastases E. Scipilliti 1 , S. Falivene 2 , V. Borzillo 2 , R. Di Franco 3 , V. Ravo 2 , P. Muto 2 PO-1247 Safety of CDKI combined with radiotherapy in hormone receptor positive breast cancer S. Falivene 1 , E. Scipilliti 2 , P. Ferraioli 2 , V. Ravo 2 , P. Muto 2 1 INT IRCCS Fondazione Pascale, Rdiotherapy, Naples, Italy; 2 INT IRCCS Fondazione Pascale, Radiotherapy, Naples, Italy