Sensitivity and specificity are 2 basic features of a diagnostic experiment. Sensitivity refers to the proportion of positive cases detected by diagnostic tests in the group of cases diagnosed using standard diagnostic methods, in which a higher sensitivity indicates a lower rate of missed diagnosis. Specificity refers to the proportion of negative results detected by diagnostic tests in a control group diagnosed as disease-free by standard diagnostic methods, in which a higher specificity indicates a lower rate of misdiagnosis. In this study, PET/CT was less sensitive to preoperative evaluation of lymph node metastases. In patients without preoperative neoadjuvant treatment, the pooled sensitivity (95% CI) in per-patient and per-station analyses were 0.54 (0.42–0.65) and 0.63 (0.38–0.83), respectively. In patients with esophageal squamous cell carcinoma, the pooled sensitivity in per-patient analysis was 0.57 (0.46–0.68). This difference may be related to micrometastasis in distant lymph nodes. Studies have shown that most distal metastatic lymph nodes have diameters < 6 mm, while the PET/CT diagnostic criteria are ≥ 1 cm in diameter, thus resulting in a lower diagnostic sensitivity.
The positive and negative likelihood ratios are more clinically significant compared to sensitivity and specificity. The likelihood ratio reflects the credibility of the diagnosis: the higher the positive likelihood ratio, the more likely it is to be a true positive finding when the test result is positive; similarly, the lower the negative likelihood ratio, the more likely it is to be a true negative finding when the test result is negative. It is generally accepted clinically that a positive likelihood ratio greater than 10 or a negative likelihood ratio less than 0.1 indicate a significantly increased possibility of diagnosis or exclusion. In this study, regardless of pathological type or if limited to squamous cell carcinoma patients, without preoperative neoadjuvant treatment, the positive likelihood ratios based on per-patient analysis were lower, at 2.9 (1.8, 4.8) and 2.5 (1.4,4.3), respectively. Per-station analysis resulted in a positive likelihood ratio of 16.4 (12.1, 22.3) and a negative likelihood ratio of only 0.39 (0.21, 0.73). These data indicate that PET/CT is less accurate for assessing lymph node metastases.
Therefore, the prediction of the prognosis in patients with EC should consider the state of pathological LN metastases rather than residual primary tumors. Additionally, because the size of the lymph nodes after neoadjuvant therapy is not always related to the treatment response, PET/CT as an indicator of biological activity is conducive to the detection of lymph node status, especially after preoperative treatment. The present study analyzed the accuracy of PET/CT evaluation of lymph node metastasis in EC following neoadjuvant therapy, showing pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic ratios (95% CI) of 0.53 (0.35–0.70), 0.96 (0.86–0.99), 13.0 (4.8–34.8), and 0.49 (0.35–0.69), respectively. These values are similar to those of patients undergoing direct surgery, suggesting that neoadjuvant therapy has little effect on the ability of PET/CT to predict lymph node status.
The present study also showed that PET-CT has high specificity but a relatively low sensitivity for the detection of lymph node status. This finding allows doctors to better understand and implement PET-CT in clinical practice. The high specificity of PET-CT for the detection of lymph node status can be used to confirm that lymph nodes are not metastasized. Surgery for EC is generally performed in 3 fields but is not suitable for every patient. For example, although the importance of para-recurrent laryngeal nerve lymphadenectomy (RLNL) has gradually become a consensus, it can cause serious complications such as hoarseness and choking after drinking water, which can seriously affect postoperative recovery and may be life-threatening. In these particular circumstances, PET-CT can be used to exclude patients without lymph nodes metastasis for lymph node dissection during radical surgery for EC, thereby reducing the scope of surgical cleaning, shortening the operation time, and reducing the harm of surgery.
The limitation of our meta-analysis was there were relatively few studies on the accuracy of PET/CT evaluation of lymph node metastasis of EC after neoadjuvant therapy compared to the number of studies that did not include neoadjuvant therapy, which may have affected the comparisons between these studies.
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