Abstract A2: Clinical implications of anti-angiogenic effect of regorafenib in metastatic colorectal cancer

Abstract

Abstract Introduction: Regorafenib is an oral multikinase inhibitor, which has anti-angiogenic and anti-tumor activity by inhibition of a number of angiogenic and oncogenic kinases. It induces distinct radiological changes in metastatic colorectal cancer (mCRC), which are decrease in tumor attenuation and cavitation of lung metastasis. These changes may be a result of anti-angiogenic activity, but the clinical implications of the changes are unclear. This study was designed to analyze the radiological changes in association with treatment outcome in mCRC patients treated with regorafenib. Methods: All patients were a part of a main study entitled Identification of Predictive Biomarker of Regorafenib in Refractory Colorectal Cancer: A Prospective Explorative Study (NCT01996969). Tumor attenuation measured by Hounsfield units (HU) of contrast-enhanced computed tomography (CT) scan and cavitary changes of lung metastases were evaluated in mCRC patients (N = 80) treated with regorafenib (160mg orally once daily, on days 1-21 of a 28-day cycle). Maximum standardized uptake values (mSUV) of tumor lesions at baseline and after 2 cycles of treatment were analyzed in patients whose 18-fluoro-deoxyglucose positron emission tomography (PET)-CT images were available for analysis. Treatment outcome was evaluated according to the Response Evaluation Criteria in Solid Tumors (RECIST) 1.1. The association between radiological changes and treatment outcome was analyzed. Results: A total of 141 lesions in 72 patients were analyzed with HU measurement. After 2 cycles of regorafenib treatment, 87.5% of patients had a decrease in tumor attenuation. Median change in tumor attenuation was -23.9% (range -61.5% to 20.7%). Lesional attenuation changes were modestly associated with changes in mSUV in PET-CT scans (Pearson's r = 0.38, p<0.001). Among 53 patients with lung metastases, 17 patients (32.1%) developed cavitary changes after treatment. New cavitation was observed in 15 patients and 6 had increases in pre-existing cavity size. Neither of the radiological changes was associated with disease control rate, progression-free survival, or overall survival. At the time of progressive disease (PD) according to RECIST 1.1, tumor attenuation was lower than baseline in 86.0% (43/50) of patients and cavitary change of lung metastases persisted without refilling in 88.2% (15/17) of patients. Conclusions: Regorafenib showed prominent anti-angiogenic activity in mCRC represented by the radiological changes. Although the changes were not associated with treatment outcome, it was persistently observed at the time of PD by RECIST 1.1. The results suggest the possibility of inadequacy of current conventional response evaluation paradigm in treating mCRC patients with regorafenib. We may need to develop alternative evaluation and treatment strategies considering the anti-angiogenic activity. Citation Format: Yoojoo Lim, Sae-Won Han, Jeong Hee Yoon, Jeong Min Lee, Jung Min Lee, Jin Chul Paeng, Jae-Kyung Won, Gyeong Hoon Kang, Seung-Yong Jeong, Kyu Joo Park, Kyung-Hun Lee, Jee Hyun Kim, Tae-You Kim. Clinical implications of anti-angiogenic effect of regorafenib in metastatic colorectal cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A2.