Surgical resection is a widely accepted procedure for patients with lung metastases. When analyzing survival data, patients with single metastasis and a disease-free interval (DFI) more than 2 years had the best survival. However, there are currently no biological predicting factors that can affect prognosis. Molecular imaging employing 18F-FDG-PET/CT enables in-vivo visualization, characterization and measurement of biological process in tumor at the molecular and cellular level. In this scenario, the aim of our study was to evaluate the prognostic value of 18F-PET/CT SUVmax in patients with colorectal lung metastasis submitted to surgical resection and to in-vivo identify patients with more aggressive metastatic tumor phenotype.
We identified 42 consecutive patients with colorectal lung metastases submitted to surgical resection who had undergone preoperative 18F-PET/TC in our Nuclear Medicine Department from 2004 to 2012. A total of 52 lesions were removed. We reviewed all 42 scans and we calculated SUVmax of each pulmonary lesion. In those patients who had more than one lesion, we considered the highest SUVmax of all nodules. In all patients we retrospectively analyzed age, sex, 18F-PET/CT SUVmax of lesions, DFI, preoperative serum CEA level, number and size of resected metastases, type of surgical intervention, and the presence of lymph nodes metastasis, in order to identify factors affecting the long-term prognosis.
Our cohort was composed of 12 women and 30 men, aged 40-79 years (mean 65). 18F-FDG PET/CT SUVmax was 7.13±5.1 (range 1-22, median 5.35). DFI was 30 months (range 3-78). Preoperative CEA level > 5 ng/dL occurred in 14/24 cases. Type of surgery was wedge resection and lobectomy in 40 and 10 cases, respectively. Size of lesion ranged 1-5 cm (mean 2.4). Mediastinal lymph nodes were sampled in 28 patients, with detection of metastases in 10/28. Five-year disease free survival (DFS) and 5-year disease-correlated survival (DCS) were 48% and 55% respectively. According to univariate analysis, factors favorably affecting prognosis were single metastasis, DFI>24 months, the absence of mediastinal lymph node metastases and SUVmax<5.35. According to multivariate analysis, independent prognostic factors were single metastasis, DFI>24 months and SUVmax<5.35. Patients with DFI>24 months showed 5-year DFS of 65% and 5-year DCS of 68%. Patients with SUVmax<5.35 showed 5-year DFS of 65% and 5-year CDS of 70%. Kaplan-Meier plot demonstrated a significant lower 5-years DFS in patients with preoperative 18F-FDG PET/CT SUVmax>5.35 (Log-rank test P=0.018). Patients with single metastasis (n=10), DFI>24 months and SUVmax<5.35 (n=15), showed 5-year DFS of 72%.
According to our results, preoperative value of SUVmax<5.35 in patients with colorectal lung metastases represent a significant factor affecting a favorable long-term prognosis, beside DFI>24 months and the presence of a single metastasis. Higher glycolytic activity detected by 18F-FDG PET/CT in-vivo identify those patients with more aggressive metastatic tumor phenotypes.

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