Letter to the Editor: “Efficacy of contrast-enhanced FDG PET/CT in patients awaiting liver transplantation with rising alpha-fetoprotein after bridge therapy of hepatocellular carcinoma”
by Sami Akbulut, Tevfik Tolga Sahin (akbulutsami@gmail.com)
Efficacy of contrast-enhanced FDG PET/CT in patients awaiting liver transplantation with rising alpha-fetoprotein after bridge therapy of hepatocellular carcinomaDear Editor,
We read with great interest the recent article published by Refaat and colleagues [1]. The authors stated that they found a significant correlation between the alpha-fetoprotein level and maximum standardised uptake value (SUVmax) ratio. We would like to express our reservations about the accuracy of this statement.
It is a statistically correct approach for the authors to use the non-parametric Spearman’s correlation coefficient (rs) to show the relationship between two continuous variables that are not normally distributed. However, it is seen that an error was made in the interpretation of the obtained result. As known, the correlation coefficient varies between -1 and 1 (-1 ≤ rs ≤1) , and the coefficient approaching 1 values in both directions indicates that the relationship is strong.
The authors stated that there was a significant and strong correlation between blood alpha-fetoprotein level and SUVmax values obtained in FDG-PET/CT (r = 0.2283; p = 0.0224). In our opinion, the comments of the authors on this subject are far from correct. The absolute value of rs, known as the correlation coefficient between 0.20-0.39, indicates that this relationship is a positive but weak-poor relationship [2, 3]. Some other authors even state that if the correlation coefficient between the two variables varies from 0.00 to 0.30, this relationship is meaningless enough to be neglected [4, 5]. A p value of < 0.05 indicates that the relationship is statistically significant, but p value does not indicate the strength of the relationship.
One of the aims of this study was to calculate the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of FDG PET / CT to predict tumor recurrence. Another aim was to show the correlation between AFP and SUVmax values in predicting recurrence.
Considering the reasons presented above, we think that the correlation arm of this study should not be taken into account and readers should read the article with this awareness.