Clinical Outcomes and Progression Pattern of Patients with Complete Metabolic Response by 18F-FDG PET-CT in Patients with Metastatic Colorectal Carcinoma

Abstract

PURPOSE: To characterise clinical outcomes and progression patterns in patients with metastatic colorectal cancer (mCRC) who received systemic chemotherapy and achieved complete metabolic response (CMR) on 18F-FDG PET-CT. METHOD AND MATERIALS: Retrospective review was conducted on patients with mCRC who received systemic chemotherapy and underwent serial 18F-FDG PET-CT in a tertiary referral centre. CMR was defined as all indexed lesions becoming eumetabolic or hypometabolic to liver. Patient characteristics including pre-treatment status, treatment received, time to achieve CMR, progression free (PFS) and overall survival (OS) were recorded. Comparison was also made with corresponding tumour response on contrast enhanced CT (CECT) by Response Evaluation Criteria in Solid Tumour (RECIST). RESULTS: Between 2008-2011, 356 patients with mCRC underwent treatment and 34 achieved CMR with a median 4 cycles of chemotherapy. Lymph nodes(LNs) are the commonest sites(33.5%) to achieve CMR, followed by liver(28.8%) and lung(12.7%). The median PFS and OS were 15 and 51 months from diagnosis, 10 and 40 months from CMR respectively. 21(61.8%) patients subsequently progressed. Amongst them, 3(8.82%) achieved further CMR and followed by second progression. 21(87.5%) progression cases included new location and bone was the commonest new site. 11 progression cases(45.8%) involved treated lesions and liver was the commonest for treated lesions to progress. The median time for progression was 6 months from CMR. Those with progression in treated lesions had better prognosis than those with new metastases only(median OS 36 vs 22 months, p=0.04). Complete response(CR) by RECIST on CECT was shown in 62% and the rest showed partial response(PR) only. Patients with single-site metastases were more likely to achieve CR(57% vs 14%, p=0.02). No statistical significance was found between two groups of CR and PR in patients' prognosis(p=0.07). CONCLUSION: Patients who achieved CMR have favourable clinical outcomes and LNs are the commonest sites to achieve CMR. The prognosis was independent of the RECIST on CECT. Over half patients subsequently progressed, of which bone and liver were the commonest sites of progression for new and treated lesions, respectively. CLINICAL RELEVANCE/APPLICATION: CMR on 18F-FDG PET defines a subgroup of mCRC patients with favourable prognosis. Understanding the pattern of recurrence facilitate decision making for more aggressive local treatment.