Quantitative PET factors predictive of the response to therapy in solid tumors: which is the best?

(99m)Tc-Annexin A5 quantification of apoptotic tumor response: a systematic review and meta-analysis of clinical imaging trials

PURPOSE

(99m)Tc-Annexin A5 has been used as a molecular imaging probe for the visualization, characterization and measurement of apoptosis. In an effort to define the quantitative (99m)Tc-annexin A5 uptake criteria that best predict tumor response to treatment, we performed a systematic review and meta-analysis of the results of all clinical imaging trials found in the literature or publicly available databases.

METHODS

Included in this review were 17 clinical trials investigating quantitative (99m)Tc-annexin A5 (qAnx5) imaging using different parameters in cancer patients before and after the first course of chemotherapy and/or radiation therapy. Qualitative assessment of the clinical studies for diagnostic accuracy was performed using the QUADAS-2 criteria. Of these studies, five prospective single-center clinical trials (92 patients in total) were included in the meta-analysis after exclusion of one multicenter clinical trial due to heterogeneity. Pooled positive predictive values (PPV) and pooled negative predictive values (NPV) (with 95% CI) were calculated using Meta-Disc software version 1.4.

RESULTS

Absolute quantification and/or relative quantification of (99m)Tc-annexin A5 uptake were performed at baseline and after the start of treatment. Various quantitative parameters have been used for the calculation of (99m)Tc-annexin A5 tumor uptake and delta (Δ) tumor changes post-treatment compared to baseline including: tumor-to-background ratio (TBR), ΔTBR, tumor-to-noise ratio, relative tumor ratio (TR), ΔTR, standardized tumor uptake ratio (STU), ΔSTU, maximum count per pixel within the tumor volume (Cmax), Cmax%, absolute ΔU and percentage (ΔU%), maximum ΔU counts, semiquantitative visual scoring, percent injected dose (%ID) and %ID/cm(3). Clinical trials investigating qAnx5 imaging have included patients with lung cancer, lymphoma, breast cancer, head and neck cancer and other less common tumor types. In two phase I/II single-center clinical trials, an increase of ≥25% in uptake following treatment was considered a significant threshold for an apoptotic tumor response (partial response, complete response). In three other phase I/II clinical trials, increases of ≥28%, ≥42% and ≥47% in uptake following treatment were found to be the mean cut-off levels in responders. In a phase II/III multicenter clinical trial, an increase of ≥23% in uptake following treatment was found to be the minimum cut-off level for a tumor response. In one clinical trial, no significant difference in (99m)Tc-annexin A5 uptake in terms of %ID was found in healthy tissues after chemotherapy compared to baseline. In two other clinical trials, intraobserver and interobserver measurements of (99m)Tc-annexin A5 tumor uptake were found to be reproducible (mean difference <5%, kappa =  0.90 and 0.82, respectively) and to be highly correlated with treatment outcome (Spearman r = 0.99, p < 0.0001). The meta-analysis demonstrated a pooled positive PPV of 100% (95% CI 92 - 100%) and a pooled NPV of 70% (95% CI 55 - 82%) for prediction of a tumor response after the first course of chemotherapy and/or radiotherapy in terms of ΔU%. In a symmetric sROC analysis, the AUC was 0.919 and the Q* index was 85.21 %.

CONCLUSION

Quantitative (99m)Tc-annexin A5 imaging has been investigated in clinical trials for the assessment of apoptotic tumor responses. This meta-analysis showed a high pooled PPV and a moderate pooled NPV with ΔU cut-off values ranging between 20% and 30%. Standardization of quantification and harmonization of results are required for high-quality clinical research. A standardized uptake value score (SUV, ΔSUV) using quantitative SPECT/CT imaging may be a promising approach to the simple, reproducible and semiquantitative assessment of apoptotic tumor changes.

Large cell neuroendocrine carcinoma of the lung: CT and FDG PET findings

PURPOSE

To evaluate the CT and (18)fluorine FDG PET findings of large cell neuroendocrine carcinomas (LCNECs) of the lung and to evaluate whether CT and FDG PET findings can help predict the clinical outcome.

MATERIAL AND METHODS

Thirty-one patients (Male:Female=29:2; mean age, 69 years) who underwent surgical resection of an LCNEC of the lung were included in this retrospective study. The tumours were assessed with respect to morphologic characteristics and the maximum standardised uptake value (SUVmax) on pre-operative CT and FDG PET. For patients undergoing curative resection (n=26), disease-free survival was evaluated using the Kaplan-Meier test. The prognostic significance was assessed using a multivariate Cox proportional hazards regression analysis.

RESULTS

The mean tumour diameter was 3.8 ± 2.1cm. Eight tumours (25.8%) were located centrally in the lung, and 23 (74.2%) were located peripherally. The margins were lobulated in 29 patients (93.5%) and well defined in 20 (64.5%). The mean SUVmax was 9.0 ± 3.8. The five-year disease-free survival rate was 46.3%. The shorter disease-free survival was related to the TNM stage greater than stage I, no lobulated margin of a tumour, a SUVmax >12.9 of a tumour, a long diameter >5.6 cm of a tumour, or female gender (P=0.115, P=0.134, P=0.056, P=0.168, P=0.113, respectively). The multivariate analysis indicated that a long diameter >5.6 cm (hazard ratio, 9.265; 90% confidence interval (CI), 1.996-42.992; P=0.017), female gender (hazard ratio, 5.579; 90% CI, 1.398-22.264; P=0.041), no lobulated margin (hazard ratio, 9.955; 90% CI, 1.433-69.136; P=0.051), and SUVmax >12.9 (hazard ratio, 4.062; 90% CI, 1.235-13.368; P=0.053) were independent predictors of shorter disease-free survival.

CONCLUSIONS

LCNECs of the lung more commonly occurred peripherally and exhibited well-defined and lobulated margins on CT. The mean SUVmax was consistent with malignant tumours. Female gender, a larger tumour diameter, no lobulated margin, and higher SUVmax were poor prognostic factors.