Abstract No. 254 - KRAS mutant metastatic colorectal cancer;is there a role for Yttrium-90 microsphere radioembolotherapy?

Abstract

Purpose Yttrium-90 microsphere radioembolotherapy (Y90mRE) and EGFR receptor inhibitors (cetuximab, panitumumab) have been utilized predominantly in chemotherapy exposed metastatic colorectal cancer (MCRC) patients. Recent evidence supports the benefit of EGFR receptor inhibitors exclusively in non-mutant KRAS status and has divided MCRC into 2 distinct therapeutic groups; mutant and non-mutant KRAS status. The void of options for KRAS mutant MCRC has created opportunities for a myriad of alternate approaches including Y90mRE, however it is unknown if Y90mRE may exhibit a similar lack of benefit in this cohort. As chemotherapy refractory KRAS mutant MCRC forms a dominant indication of referrals for Y90mRE, we sought to negate the possibility of therapeutic futility by retrospectively analyzing the outcomes of MCRC therapy based on KRAS status at our institution. Materials and Methods Data detailing patient demographics, systemic therapy received, activity of Y90 microspheres (SIR-Spheres ® , Sirtex Medical, Australia or TheraSphere ® , Nordion, Canada) delivered, RECIST responses and TTP were noted. Results 35 patients (16 female, mdn age 63 yrs) met study criteria. All patients had received systemic chemotherapy before Y90mRE. Median activity of Y90 delivered was 40.5 mCi (range 6.7-71). KRAS status was mutated in 17 and non-mutated in 18 patients respectively. Partial responses were noted in 1 KRAS mutant and 4 KRAS non-mutants. Median TTP was 6 months for KRAS mutants and 7 months for non-mutants respectively. Conclusion MCRC KRAS mutational status did not negate responses to Y90 mRE however the magnitude of the clinical benefit in this cohort remains to be determined.