The impact of complete metabolic response in the treatment of metastatic colorectal cancer

Abstract

AIM: Molecular imaging with 18F-FDG PET scan is increasingly used for monitoring of treatment response in metastatic colorectal cancer. While there is no widely accepted standard for defining partial response, metabolic complete response (mCR) appears as a more reproducible endpoint.We performed a retrospective study to evaluate the impact of mCR on both treatment outcomes and treatment plan. METHODS: Patients who were referred to our department for further management of colorectal cancer from Jan 2008 to Dec 2011 were retrospectively reviewed. They were included for subsequent analysis if [1] achieved mCR on 18F-FDG PET scan during first-line therapy, [2] serial PET scans (>= 2) available for demonstration of change in 18F-FDG avidity. The primary endpoint was progression-free survival (PFS). Secondary endpoint were overall survival (OS), time-to-mCR (TTm) and impact ofmCR on subsequent treatment plan. RESULTS: Among the 1007 patients referred to us, 356 patients (35%) received systemic therapy for metastatic disease and 202 of them (20%) had PET scan done during the course of systemic therapy. Forty-three patients achieved mCR and 37 of them fulfilled all the criteria for subsequent analysis. mCR was achieved after a median of 4 cycles of systemic therapy (Range 3-12 cycles) after a median TTm of 14weeks (95% CI 12.5-15.5). Subsequent treatment was not altered in 21 patients (56.7%) who had planned drug holiday after six months of therapy. Six and ten of the remaining patients received maintenance therapy and consolidation treatment (resection or radiotherapy), respectively. After a median follow up time of 33 months, the median PFS and OS was 14.4 months (95% CI 10.3 to 18.6) and 47.1 months (95% CI 36.8 to 57.4), respectively. Normal initial CEA (<5ng/ml) was significant predictor of prolonged PFS on both univariate and multivariate analysis (p = 0.05; HR 3.49, 95% CI 1.45–8.37). Liver-onlymetastasis, Kras mutation status, use of any target therapy or coexisting radiological complete response were not significant predictor of survival in patients who achieved mCR. CONCLUSIONS: Favorable outcomes were observed in patients who achieved mCR on 18F-FDG PET scan. Its current impact on treatment decision remains elusive and further studies warranted.