In the current issue of the Journal, Alawadhi et al. shared their review of the accuracy
of fine-needle aspiration (FNA) cytology for detecting cancer in resected thyroid
nodules at a referral center, namely, The Cleveland Clinic Abu Dhabi.[[1]] The article renewed the increased interest over the past few years in the epidemiology
and clinical management of thyroid cancer in the Arabian Gulf and more specifically
in the United Arab Emirates (UAE).
The advent of thyroid US in general and its wider availability in the recently developed
countries of the region have increased the incidental discovery of thyroid nodules
and hence the incidence of thyroid cancer in the region. The accumulated prevalence
of thyroid cancer among thyroid nodules has varied from 5% to 14% with peculiar peak
incidence occurring before the age of 45 years was observed by several groups.[[2]],[[3]],[[4]] The average age in this study was 41, and the median age was 40 years making it
a decade earlier than what is seen in the USA and Western countries in general. However,
the most commonly encountered type of thyroid cancer remains papillary, followed by
follicular thyroid cancer with a female-to-male ratio, swirling around a ratio of
4.9:1.
Considering that 82.1% of the subjects in this study were UAE nationals, it would
have been valuable if the authors referred to recently published local or regional
studies comprising subjects of similar or closer population background. Unfortunately,
they chose to make comparisons with data from an Egyptian study that included subjects
of minimal similarity to their study population. A meta-analysis of all published
data from the Gulf and neighboring regions is called for to explore differences and
similarities and may shed more lights on any peculiarities of the region.
FNA of the thyroid has been adopted worldwide as an efficient and reliable means for
the evaluation of thyroid nodules with a diagnostic sensitivity of 89%–98% and a specificity
of 92% and false-negative results not exceeding 10%.[[4]] In fact, locally reported false-negative rates of FNA did not exceed 6% even after
1-year follow-up.[[5]] This contrasts remarkably with the results described in the current paper.[[1]] Reporting a sensitivity as low as 52%, a negative predictive value of 64%, a high
false rate of 48%, and an accuracy of around 72% need more explanation. Such rates
would be explained by either poor sampling or interpretation or to thyroid nodule
size exceeding 4 cm where the false-negative rate would have been expected to be high.[[6]] Unfortunately, no tumor size data were reported, and negative and positive predictive
values were calculated with no preliminary knowledge of thyroid cancer prevalence
in the UAE.
Bethesda classification adopted in this study is accepted worldwide as being a reliable
method to classify and stratify thyroid nodules.[[7]] Of note, several publications from the gulf region have lately focused on the group
of indeterminate thyroid nodules (Atypia of unknown significance [AUS] and follicular
neoplasm of unknown significance) with rates of cancer varying between 20% and 45%.[[8]] This contrasts with the higher figures observed in this study (38.1% and 69.1%
for AUS and follicular neoplasm, respectively). This could be partly due to referral
bias, lack of histology review to discern the group of NIFTP, expertise variability
in cytology, and/or statistical bias. For instance, organizing cytology results as
either benign or malignant but lumping in this group benign, AUS, follicular neoplasm
subgroups is inappropriate. Also, classify histology results as either nonneoplastic
or neoplastic (suspicious for malignancy and malignant) is confusing and inappropriate.
In fact, when we did reclassify the cytology results as either benign (Bethesda 2)
or malignant (Bethesda 4 and 5) while excluding the indeterminate group, the statistical
figures changed to FNA sensitivity of 80% (vs. 50.1%); reducing the high false-negative
rate to 20% instead of 48.9% while maintaining a specificity of 90%.
Finally, the high rate of thyroid cancer stated in this study could be attributed
to either a preselection of high-risk thyroid tumors been referred to a tertiary hospital
or to incidentally discovered micropapillary thyroid cancers unrelated to the biopsied
tumors.
Overall, it is an interesting study reflecting on a local experience with unexpectedly
debatable results. Further systematic reviews and narrations of all the published
data from the region are called for to present a balanced overview of the condition
and its management.
Authors' contribution
Equal.
Compliance with ethical principles
No ethical approval is required.
