Hepatic Imaging Response To (90)Y-Microsphere Therapy Administered For Tumor Progression During Systemic Chemotherapy In Patients With Colorectal Liver Metastases

270 Background: Hepatic tumor progression after one or more lines of 5FU-based systemic chemotherapy, with or without biologic agents, is an indication for radioembolization using 90 Y microspheres. Methods: An independent imaging review following resin-only 90 Y microsphere treated cases of mCRC from July 2002 to December 2011 at 9 US institutions was conducted. A board certified radiologist systematically reviewed hepatic Computed Tomography (CT) images (portal-venous phase) at baseline and 3 months after 90 Y treatment. Tumor response was assessed using RECIST 1.0 criteria, based on a maximum of 5 target lesions. Peri-tumoral edema and necrosis; known artifacts which can affect the interpretation of RECIST response, were documented for each lesion. Kaplan Meier analysis compared survival for responders [Partial Response (PR)] vs. non-responders [Stable Disease (SD) or Progressive Disease (PD)]. Results: A total of 184 patients were studied; male (61%) and Caucasians (61%) most common, mean age 62.5 years received a median of 2 (range 1–5) lines of chemotherapy prior to 90 Y therapy. Median tumor/liver ratio at 90 Y therapy was 15% (IQR 20%). Median 90 Y activity administered was 1.18 GBq (IQR 0.55). RECIST response at 3 months was 9.8% PR (n=18), 72.3% SD (133) and 17.9% PD (33); Disease Control Rate = 82.1%. Peri-tumoral edema was documented in 33% (n=60); necrosis in 42% (79); both in 22% (40) of cases, respectively. No significant differences in background characteristics between responders and non-responders were evident (p>0.05). RECIST response at 3 months predicted survival: PR median 13.9 months (95% CI 9.2-30.3) vs. SD 11.0 (8.9-13.5) vs. PD 6.7 (5.5-8.1) [p=0.002]. Conclusions: Radiological lesion response to 90 Y therapy at 3 months must be interpreted with caution due to the significant proportions of peri-tumoral edema and necrosis encountered. Both of these artifacts may lead to either the under estimation of PR/SD or the overestimation of PD, respectively. Given these caveats, early (3 month) hepatic radiological response to 90 Y therapy appears to predict longer term prognosis.