Indian Journal of Pathology and Microbiology

: 2022  |  Volume : 65  |  Issue : 3  |  Page : 637--641

Correlation of fine needle aspiration cytology and cell block study of category III, IV, and V (TBSRTC-2017) thyroid lesions with special reference to cytokeratin-19 immunohistochemical staining

Gourab Mukherjee, Sumana Biswas, Biswajit Haldar, Tanmoy Dutta 
 Department of Pathology, North Bengal Medical College and Hospital, Darjeeling, West Bengal, India

Correspondence Address:
Gourab Mukherjee
M/1, Saratpally, Dak Bunglow Road, P.O. Midnapore, West Medinipur–721 101, West Bengal


Context: Ascertaining the role of cytokeratin-19 (CK19) and its staining pattern helps to differentiate papillary carcinoma from other thyroid lesions. Aims: To correlate fine needle aspiration cytology (FNAC) and cell block study of equivocal cases (Category III, IV, and V) with the role of CK19 staining in it. Settings and Design: A hospital-based cross-sectional observational study was designed and conducted at North Bengal Medical College and Hospital, Shusrutnagar, Darjeeling. Methods and Material: The FNAC performed and reported as per TBSRTC-2017.50 cases of Category III, IV, and V was selected for cell block study and CK19 staining followed by immunohistochemical scoring. Results: Out of 50 cases, 17 were follicular neoplasm, 21 papillary carcinoma, 6 lymphocytic thyroiditis, 1 Hürthle cell adenoma, 1 medullary carcinoma, 1 lymphoma, and 3 undifferentiated carcinomas. Among cases of papillary carcinoma, 10 showed 4+ positivity, 9 showed 3+ positivity, 2 showed focal 1+ and 2+ positivity. In the case of follicular neoplasm, 1 showed 3+ positivity, 3 cases had 1+ 2+ positivity, and 13 cases revealed negative staining. Conclusion: Role of CK19 in distinguishing papillary carcinoma of thyroid from other lesions in cytologically diagnosed Category III, IV, and V (TBSRTC-2017) cases can be demonstrated.

How to cite this article:
Mukherjee G, Biswas S, Haldar B, Dutta T. Correlation of fine needle aspiration cytology and cell block study of category III, IV, and V (TBSRTC-2017) thyroid lesions with special reference to cytokeratin-19 immunohistochemical staining.Indian J Pathol Microbiol 2022;65:637-641

How to cite this URL:
Mukherjee G, Biswas S, Haldar B, Dutta T. Correlation of fine needle aspiration cytology and cell block study of category III, IV, and V (TBSRTC-2017) thyroid lesions with special reference to cytokeratin-19 immunohistochemical staining. Indian J Pathol Microbiol [serial online] 2022 [cited 2022 Dec 6 ];65:637-641
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Full Text


Thyroid swelling is an important worldwide problem with a more common prevalence in South Asia. The fine needle aspiration cytology (FNAC) introduced later for diagnosis quickly gained acceptance and soon became an important diagnostic tool due to its good patient compliance and cost-effectiveness. However, due to limitations like sample inadequacy, low cytomorphological details, and architectural overlapping, some diagnoses were left out and some were not reliable.[1],[2],[3] The cell-block technique allows for a high cellular yield that facilitates better morphological analysis. Besides, it permits performing additional studies such as histochemical staining and immunohistochemical analysis that increase diagnostic accuracy.[4] Still, inter-observer variability and the various reporting protocols of different institutes led to diagnostic bias. The National Cancer Society Conference (NCI) participants 2007 formed “The Bethesda System of Reporting Thyroid Cytopathology (TBSRTC).” This uniform system alleviates inter-observer bias by categorizing the FNAC diagnosis into six groups with associated information about risk chances of malignancy and indication for further clear management. The diagnosis of thyroid carcinomas is straightforward in most cases, but pathologists are in a dilemma about equivocal features that necessitate the distinction of benign lesions from malignant lesions. Although the diagnostic criteria for papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC) are clearly outlined in textbooks, the application of criteria is subjective and circumstantial. Inter-observer or intra-observer doubts and disagreements in the diagnosis of follicular thyroid lesions are well documented, even among expert pathologists, in the past. Cytokeratin-19 (CK19) is extensively used in the diagnosis of thyroid lesions. Many studies have reported it as a sensitive marker in differentiating benign from malignant thyroid tumors. CK19 immunostaining as an ancillary technique in the diagnosis of papillary carcinoma is well recognized in the surgical pathology literature. Thus, our study aims to compare the FNAC report with cell block report with reference to immunostained (with CK19) slide report of equivocal thyroid swellings (TBSRTC-2017, Category III, IV, and V).


The present study's objectives included the following: correlate cytological findings with cell block histopathological finding, study the staining pattern of CK19 in all equivocal (Category III, IV and V, TBSRTC-2017) cases and assess the role of CK19 immunohistochemical staining to confirm the cytologically diagnosed papillary carcinoma.

Review of literature

The study by Dr. Zarika Ahmed, Dr. Pranita Medhi, Dr Debojit Das published in the Journal of Evolution of Medical and Dental Sciences (2015, Vol. 4, Issue 76, September 21) shows that cell block preparations are superior in getting cytomorphological details of thyroid lesions than the conventional FNAC.[5]

The study published by Dr. Vimal Bhandari, Dr. Yogesh Yadav, Dr. Geetika Khanna, Dr. Mrinalini Sharma, Dr. Mohit Singh, and Dr. Rajni (“Efficacy of Cytokeratin 19 Expression on Fine Needle Aspiration Cell Blocks in Pre-operative Diagnosis of Malignant Thyroid Neoplasms) found a high positive predictive value for CK19 staining in diagnosing papillary carcinoma of thyroid.[6]

 Materials and Methods

Study Design: Hospital-based observational study with a cross-sectional design.

Study Setting: A tertiary care hospital in North Bengal.

Place of Study: Department of Pathology, Department of General Surgery, Department of General Medicine, and Department of Radiology at North Bengal Medical College and Hospital, Shusrutnagar, Darjeeling.

Period of Study: April 2019 to March 2020.

Ethical Clearance: Ethical clearance was obtained from the Institutional Ethics Committee of the North Bengal Medical College and Hospital, Shusrutnagar, Darjeeling.

Study Population: Patients with thyroid swelling attending the Department of Pathology, Department of General Surgery, Department of General Medicine, and Department of Radiology.

Sample Size: As this is a hospital-based study, a total of 50 patients referred to the Department of Pathology for FNAC of thyroid swelling and fulfilling the inclusion criteria and then cytologically diagnosed for TBSRTC Category III, IV, and V cases were recruited for the study.

Inclusion Criteria: All clinically and radiographically diagnosed cases of thyroid swelling, referred to the Department of Pathology for FNAC, irrespective of age and sex, were included.

Exclusion Criteria: Patients not giving consent and patients having severe illness and patients taking cytotoxic drugs were excluded from the study.

Study technique:

The study sample included those patients attending the General Surgery OPD, General Medicine OPD, and the Radiology department with clinically diagnosed thyroid swelling.Study subjects were selected as per inclusion and exclusion criteria.Patients were informed about the study in detail and their written consent was obtained. After the recruitment process was completed, the study proforma was finalized.Material was aspirated from thyroid swelling with or without USG guidance. For ultrasonography guidance, a Cameco syringe pistol fitted with 10 cc syringe was used.Air-dried and alcohol-fixed smears were prepared from aspirated material.FNAC smears were stained with Leishman-Giemsa and Haematoxylin and Eosin stain.Reporting of FNAC slides for cytological diagnosis as per TBSRTC-2017.Cases with cytological diagnosis of TBSRTC (2017) Category III, IV, and V were selected for cell block preparation.Cell blocks were prepared from aspirates of 2nd pass by plasma thrombin clot method. After thorough processing, paraffin sections were stained by Haematoxylin and Eosin stain.Diagnosis of cell blocks.Further histopathological follow-up.Immunohistochemical staining was done by labelled Horse Radish Peroxidase polymer technique. CK19 was used on the cell blocks and the findings were noted.Definitive diagnosis/final diagnosis.

Immunohistochemical scoring:


Data Collection: All relevant data were collected using semi-structured, pretested questionnaire and study proforma.

Statistical Analysis: Collected data were entered in Microsoft Excel data sheet. Data were organized and presented using principles of descriptive statistics. Outcome variables were tested applying appropriate statistical methods and the SPSS software [Table 1], [Table 2], [Table 3] and [Figure 1], [Figure 2], [Figure 3].{Table 1}{Table 2}{Table 3}{Figure 1}{Figure 2}{Figure 3}


Considering histopathological diagnosis as the gold standard,

Sensitivity, specificity, positive predictive value, and negative predictive value of cell block were 84.2, 71.4%, 62.5%, and 89.4%, respectively.

Applying the Chi-square test, we found that the P < 0.005 for all the lesions, which means the test is statistically significant.

Diagnostic accuracy of CK19 (considering CK19 3 + value cutoff): 92%.


This study demonstrates the occurrence of equivocal lesions of thyroid (TBSRTC Category III, IV, and V) in patients attending a tertiary care center of North Bengal and the correlation of their diagnosis in FNAC and cell block with the use of CK19 in the immunohistochemistry for assessment of staining pattern in these lesions with diagnostic role in papillary carcinoma. Among the 50 selected cases, cytologically 20 were diagnosed as atypia of undetermined significance/follicular lesion of undetermined significance (TBSRTC Category III; 40%), 15 were follicular neoplasm/suspicious for follicular neoplasm (TBSRTC Category IV; 30%), and 15 were suspicious for malignancy (TBSRTC Category V; 30%). Among the 15 cases suspicious for malignancy, 10 were suspicious for PTC, 3 were suspicious for malignancy NOS (not otherwise specified), 1 was suspicious for medullary carcinoma, and 1 was suspicious for lymphoma.

These 50 cases when subjected to cell block study, cytologically diagnosed AUS/FLUS (Atypia of Undetermined Significance (AUS)/Follicular Lesion of Undetermined Significance, TBSRTC, Category III) cases revealed 6 cases of lymphocytic thyroiditis, 7 cases of follicular neoplasm, and 7 cases of papillary carcinoma, whereas in the case of cytologically diagnosed FN/SFN (Follicular neoplasm/Suspicious for follicular neoplasm, TBSRTC, Category IV) cases, 12 cases of follicular neoplasm, 1 case of Hürthle cell adenoma, and 2 cases of papillary carcinoma were found. For cytologically diagnosed TBSRTC Category V cases, 10 cases were diagnosed as papillary carcinoma, only 1 case revealed to be medullary carcinoma thyroid, 3 cases came out to be undifferentiated carcinoma, and only 1 case was diagnosed as lymphoma of thyroid. In our present study, the sensitivity and specificity measured were 84.2% and 71.4%, respectively. Similar findings were reported in a study by Parate N Sanjay et al.[7] in 2019, where the sensitivity of cell block was 90.91%.

The histopathological study revealed 25 cases of papillary carcinoma, 1 medullary carcinoma, 3 undifferentiated carcinomas, 1 lymphoma, 6 lymphocytic thyroiditis, 6 nodular goiter, 4 NIFTP (noninvasive follicular thyroid neoplasm with papillary-like nuclear features), 3 follicular adenoma, and 1 Hürthle cell adenoma.

Cytokeratins are intermediate filament proteins responsible for the structural integrity of epithelial cells. CK19 is a type I keratin encoded by the KRT19 gene. It has been proposed as an immunohistochemical marker to distinguish PTC from other tumors with follicular pattern and with benign lesions. Several studies have reported the diffuse positive reactivity for CK19 in PTCs. Liberman et al.[8] reported uniform reactivity for CK19 in 100% of papillary tumors. In their study, 9 out of the 10 follicular adenomas stained were weakly positive. In another study, 16 out of 18 cases of PTCs showed moderate to strong staining with CK19 and almost all non-neoplastic lesions stained negative. Cheung et al.[9] also reported diffuse CK19 staining in 80% of usual variants of papillary carcinoma. With majority of the studies affirming the role of CK19 immunoreactivity for diagnosis of papillary carcinoma thyroid, the practical usefulness of CK19 for differential diagnosis of various benign and malignant thyroid lesions remains an inadequately explored area. Zhu et al.[10] also concluded that CK19 was useful not only for the differentiation of benign and malignant papillary structure but also for the differential diagnosis of PTC and FTC. They observed that CK19 expression was diffuse and strong in the papillary structure of PTC, but weak and focal in the papilla of tissue with benign disease. And also, the expression of CK19 in follicular PTC was significantly higher than in FTC.[11],[12]

In our study, cell block with immunohistochemical study with CK19 revealed 17 cases of follicular neoplasm (34%), 21 papillary carcinoma (comprising most of the cases at 42%), 6 lymphocytic thyroiditis (12%), 1 Hürthle cell adenoma (2%), 1 medullary carcinoma (2%), 1 lymphoma (2%), and 3 undifferentiated carcinomas (6%). In our study, CK19 staining gave strong positive-4+ in 10 cases (20%), diffuse positive-3+ in 10 cases (20%), focal positive 1+, 2+ in 5 cases (10%), and negative staining 0+, in 25 cases (total 50%). Among the cases of papillary carcinoma, 10 showed 4+ positivity, 9 showed 3+ positivity, and 2 showed focal 1+, 2+ positivity. In the case of follicular neoplasm, 1 case showed 3+ positivity, 3 had 1+ 2+ positivity, and 13 revealed negative staining. In the total 6 cases of lymphocytic thyroiditis, 3 undifferentiated carcinomas, 1 medullary carcinoma, 1 Hürthle cell adenoma, and 1 lymphoma showed negative staining. In the histopathological study, 13 cases of PTC showed 4+ positivity, 10 cases 3+ nd 2 cases 2+, 1+ positivity, while all other lesions showed negative staining. This is similar to the findings reported in Wa Kamal Wan Sahira et al.'s 2019[13] study, where 87.5% of papillary carcinoma cases showed strong positivity with CK19. A 2018 study by Margari Niki et al. reported a 100% positive expression rate of CK19 for papillary carcinoma in cell block material. CK19 had the highest positive expression in PTCs. Its overexpression is related to malignancy. Furthermore, it seems to be the most sensitive marker in the discrimination of PTC from benign lesions. The specificity of CK19 expression ranges from 75% to 97% for papillary carcinoma. The cases of medullary carcinoma and undifferentiated carcinoma were found to be negatively stained in this study.[14]


FNAC was inconclusive in the case of intermediate lesions of thyroid (TBSRTC Categories III, IV, and V), as all the lesions were equivocal. Thus, histopathological correlation is required to achieve a final diagnosis for which purpose the cell block study can be regarded as an appropriate adjunct. However, in our study, the cell block could not differentiate a case of follicular neoplasm into follicular adenoma or follicular carcinoma. CK19 could be used effectively to distinguish papillary carcinoma of thyroid from other benign thyroid lesions. CK19 staining pattern provided further information regarding the nature of lesions, as only papillary carcinoma showed both strong positivity (4+) and diffuse positivity (3+), whereas other papillary lesions showed weak positivity. Hence, CK19 could be used as a useful marker in distinguishing papillary carcinoma of thyroid from other lesions in a cytologically diagnosed equivocal lesion of thyroid (TBSRTC Categories III, IV, and V) and help us in diagnosis, prognosis, and treatment.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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