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. 2026 Jan 26;21:9. doi: 10.1186/s13000-026-01753-3

TTF-1, CDX-2, PAX-8 and GATA-3 immunoexpression in a large serie of extrapulmonary small cell neuroendocrine carcinomas: a study of 138 cases

Klára Pavlíčková 1, Petr Waldauf 2, Pavel Dundr 3, Marián Švajdler 4, Pavel Fabian 5, Iva Staniczková Zambo 6, Miroslava Flídrová 3, Jan Laco 7, Helena Hornychová 7, Patricie Delongová 8, Jozef Škarda 8, Jan Hrudka 9, Radoslav Matěj 1,3,9,✉
PMCID: PMC12857084  PMID: 41588454

Abstract

Background

Extrapulmonary small cell neuroendocrine carcinoma (EP-SC) is a rare malignancy with a poor prognosis. In our study, one hundred and thirty-eight EP-SCNC tissue samples underwent a complex analysis.

Method

Multicentric study included 138 high-grade small cell carcinomas exhibiting neuroendocrine morphology without known pulmonary involvement. Using TMA, we studied the possible benefit of TTF-1 (DAKO, clone 8G7G3/1, dilution 1:200), CDX-2 (DAKO, ready to use kit DAK-CDX2), PAX-8 (Cell Marque, polyclonal, dilution 1:50) and GATA-3 (Cell Marque, clone L50-823, 1:200) immunohistochemical analyses for determining the primary site of EP-SCNC origin. For statistical analyses, the Kaplan-Meier, the Cox regressions analyses, the Pearson chi-square test and the Fisher’s exact test were used.

Results

The median survival of our cohort was 11.5 months. Patients younger than 70 years had significantly better overall survival (p = 0.024).

Across the full cohort, CDX-2 positivity was found in 19 tumors (13.9%), TTF-1 in 35 tumors (25.7%), PAX-8 in 63 tumors (46.3%) and GATA-3 in 8 tumors (6.5%), regardless of tumor origin. The expression of CDX-2, PAX-8 and GATA-3 did not differ significantly among different organ systems (p = 0.2; 0.3 and 0.12), respectively. The expression of TTF-1 differed significantly in tumors from various sites of origin (p = 0.009), expressed more often in breast, pancreatic, and genitourinary tumors. Interestingly, TTF-1 expression proved to have a negative prognostic impact relative to patient survival (age-adjusted Cox regression analysis, HR = 1.62, 95%CI:1.06–2.47, p = 0.021).

Conclusion

As most patients with EP-SCNC had a metastatic presentation, finding the primary tumor origin, which is important for patient prognoses, is both challenging and important at the same time. Only TTF-1 immunohistochemical analysis proved to be helpful with this task. Moreover, a diagnosis of primary lung small cell carcinoma cannot be established based on TTF-1 positivity, since only 25.7% of EP-SCNC in our study displayed TTF-1 positivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13000-026-01753-3.

Keywords: Extrapulmonary small cell neuroendocrine carcinoma, TTF-1, CDX-2, PAX-8, GATA-3

Introduction

Extrapulmonary small cell neuroendocrine carcinoma (EP-SCNC) is a rare malignancy with a poor prognosis; the average overall patient survival is less than 12 months [1, 2]. The incidence of EP-SCNC is less than 0.4% of human malignancies [2]. Recently, molecular evidence has shown that EP-SCNC can develop late in the progression of various organ-specific carcinoma types [2]. Therefore, the incidence of extrapulmonary neuroendocrine carcinoma is increasing, which may be related to expanded systemic cancer therapy for organ-specific adenocarcinomas [3].

EP-SCNC can originate from any organ system, including the genitourinary, gastrointestinal, hepatobiliary systems, the gynecologic tract, pancreas, and the head and neck region. Most patients with EP-SCNC have metastatic disease upon presentation, therefore, the search for the primary origin site of the tumor can be challenging, and some fraction of tumors have undetermined primary sites.

CDX-2, TTF-1, PAX-8 and GATA-3

Organ-specific antigens CDX-2, TTF-1, PAX-8 and GATA-3 are routinely used to find the primary sites of metastatic adenocarcinomas. CDX-2 (caudal-related homeobox 2) is essential for intestinal cell fate specification during embryonic development. Its expression begins in the duodenum, gradually increasing through the small intestine, peaking at the ileocecal region, and then declining in the distal colon [4]. TTF-1 (thyroid-transcription factor 1) participates in the differentiation, development, and functional maintenance of the lungs, thyroid gland, and brain structures of diencephalic origin [5]. It is expressed mainly in Clara cells, type II pneumonocytes, thyroid follicular cells, the pituitary gland, and the hypothalamus [6]. PAX-8 is a transcription factor involved in the organogenesis of the thyroid gland, kidneys, and the Müllerian system. PAX-8 is therefore expressed in the thyroid and parathyroid glands, the kidneys, thymus, and female and male genital tracts [7, 8]. GATA-3 is a transcription factor important in the differentiation of breast epithelia, urothelia, and subsets of T lymphocytes [9].

This study aims to clarify the expression of organ-specific antigens CDX-2, TTF-1, PAX-8 and GATA-3 in a large cohort of EP-SCNC with various primary sites.

Materials and methods

Sample selection

This multicenter study analyzed 138 diagnosed cases of extrapulmonary small cell neuroendocrine carcinoma (EP-SCNC) over 24 years (1999–2023). It included high-grade small cell carcinomas exhibiting neuroendocrine morphology, characterized by scant cytoplasm, finely granular chromatin lacking nucleoli, brisk mitotic activity, frequent apoptotic bodies, and necrosis, but without known pulmonary involvement. Inclusion was independent of neuroendocrine marker expression, though all cases underwent marker analysis. Specimens were sourced from the archives of participating pathology departments.

Formalin-fixed, paraffin-embedded (FFPE) tissue samples from biopsies and surgical resections were collected for analysis. Two pathologists (R.M. and K.P.) examined hematoxylin and eosin-stained slides, selecting representative regions from FFPE blocks for tissue microarray (TMA) construction.

Various clinical data were collected, including sex, age at diagnosis, and primary origin of the tumor. Overall survival (OS), the time between the initial diagnosis and death, was taken from records kept by the Institute of Health Information and Statistics of the Czech Republic. None of the patients received prior oncological therapy before biopsy/surgery.

Immunohistochemical analysis

Immunohistochemistry was performed on tissue microarrays (TMAs) using 4 μm-thick FFPE tissue sections. Regions predominantly infiltrated by viable small cell carcinoma cells were identified and used for TMAs construction. Two tissue cores (each 2.0 mm in diameter) were taken from the original bioptic tissue block using a TMA Master tissue microarray instrument (3DHISTECH Ltd., Budapest, Hungary). Using TMA, immunohistochemistry (IHC) was performed using organ-specific transcription factors CDX-2 (DAKO, ready to use kit DAK-CDX2), TTF-1 (DAKO, clone 8G7G3/1, dilution 1:200), PAX-8 (Cell Marque, polyclonal, dilution 1:50) and GATA-3 (Cell Marque, clone L50-823, 1:200). In instances where suitable section in TMA was unavailable for immunohistochemistry, analyses were repeated using material from the original blocks.

Statistical analysis

All analyses were performed using R version 4.5.0 and RStudio [10]; survival analyses were carried out using the survival package 3.8-3.8, survminer 0.5.0 [11], and adjustedCurves 0.11.2 [12]. Continuous data are expressed as means and standard deviations or medians with 25th and 75th percentiles (or interquartile range, IQR), depending on the normality of the distribution. Binary and categorical data are expressed as counts and percentages.

For OS analysis, a Kaplan-Meier analysis was performed with 95% confidence intervals (95% CIs) calculated using the log-log method and p-values from the log-rank test. Univariate and age-adjusted Cox regressions were also performed for age and tumor location, expressed as unadjusted and age-adjusted hazard ratios (HR) with 95% CI. For OS analysis, patients were censored at five years.

The Pearson chi-square test and Fisher’s exact test were used as appropriate to assess associations between categorized variables. Categorized parameters included primary tumor location and age (≤ 70).

Samples were considered CDX-2, TTF-1, PAX-8 and GATA-3 positive if at least 5% of cells displayed moderate to strong nuclear staining, as summarized in detail elsewhere [13].

P values < 0.05 were considered statistically significant.

Results

Clinical description of the cohort

Of the 138 Caucasian patients included in the analysis, 86 were males (62.3%) and 52 were females (37.7%), with a mean age of 67.0 years (ranged 38.2–94.1 years) at the time of diagnosis. Median survival was 11.5 months (95% CI 8.3–14.5 months), and five-year survival was 16.2%.

The primary EP-SCNC tumor location was the genitourinary (male genital and urinary) tract in 71 patients (51.4%), gastrointestinal tract (esophagus, stomach, and intestine) in 20 patients (14.5%), gynecological tract in 16 patients (11.6%), pancreas in 5 patients (3.6%), head and neck in 8 patients (4.4%), breast in 5 patients (3.6%), hepatobiliary system in 3 patients (2.2%), and the skin in 1 patient (0.7%). There were 9 (6.5%) EP-SCNCs with unknown primary sites. In all analyzed cases, a primary pulmonary origin was excluded based on clinical documentation. All specimens were from tumor resections/biopsies (95 biopsies and 43 resections) of primary tumors, apart from the 9 EP-SCNCs with unknown primary sites.

The patient’s age proved to be an independent prognostic marker (Kaplan-Meier survival analysis comparing patients by age: Patients under 70 years showed a median survival of 12.3 months (95% CI: 9.6–28.2) versus 7.6 months (95% CI: 4.9–13.7) for patients over 70 years (p = 0.024).

Immunohistochemical analysis

Among the entire cohort, irrespective of tumor origin, 19 (13.9%) tumors were CDX-2 positive, 35 (25.7%) tumors were TTF-1 positive, 63 (46.3%) tumors were PAX-8 positive and 8 (6.5%) tumors were GATA-3 positive (Fig. 1). The expressions of CDX-2, TTF-1, PAX-8 and GATA-3 with respect to tumor origin are shown in detail in Fig. 2. Expression of CDX-2, TTF-1, PAX-8 and GATA-3 in different organs is shown in Supplementary Material 1.

Fig. 1.

Fig. 1

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EP-SCNC of colon exhibiting nuclear CDX-2 positivity, with positivity of colon crypts (crypts of Lieberkühn) serving as an internal control, 200×, (A). EP-SCNC with nuclear PAX-8 positivity, 200×, (B). EP-SCNC exhibiting strong nuclear TTF-1 positivity, 200×, (C). EP-SCNC of urinary bladder exhibiting strong nuclear GATA-3 positivity, 200x, (D)

Fig. 2.

Fig. 2

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Distribution of TTF-1 (blue), CDX-2 (red), PAX-8 (green) and GATA-3 (purple) in EP-SCNCs with respect to tumor origin

The expression of CDX-2, PAX-8 and GATA-3 did not differ significantly among different organ systems (p = 0.2; 0.3 and 0.12, respectively). At the same time, CDX-2, PAX-8 and GATA-3 expression did not have an impact on patient survival (p = 0.85; 0.84 and 0.49, respectively). Regarding CDX-2, there were 8 (11.1%) positive genitourinary tumors, 6 (30.0%) positive gastrointestinal tumors, 1 (6.3%) positive gynecological tumor, and 2 (33.3%) positive pancreatic tumors. In PAX-8, there were 34 (46.6%) positive genitourinary tumors, 10 (62.5) positive gynecological tumors, 5 (25.0%) positive gastrointestinal tumors, 5 (62.5%) positive head and neck tumors, 2 (40.0%) positive breast tumors, 2 (66.7%) positive tumors of hepatobiliary origin, and 1 (20.0%) positive pancreatic tumor. In GATA-3, there was 1 positive skin tumor (100%), 1 positive breast tumor (20%) and 6 positive genitourinary tumors (9.2%).

Concerning TTF-1 immunohistochemistry, 25 (34.7%) genitourinary tumors displayed TTF-1 positivity, from other locations, there were 4 (20.0%) TTF-1 positive gastrointestinal tumors, 3 (60.0%) TTF-1 positive breast tumors, 2 (40.0%) TTF-1 positive pancreatic tumors, and 1 (12.5%) TTF-1 positive head and neck tumors. Therefore, the expression of TTF-1 differed in tumors of various sites of origin (p = 0.009). Moreover, TTF-1 expression proved to have a prognostic impact on patient survival, as shown by age-adjusted Cox regression analysis (HR = 1.62, 95% CI: 1.06–2.47, p = 0.021) and Kaplan-Meier analysis (p = 0.024; Fig. 3).

Fig. 3.

Fig. 3

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Kaplan-Meier curve documenting significantly longer OS in those with TTF-1 positive tumors

Discussion

Our study examined a cohort of 138 extrapulmonary small-cell neuroendocrine carcinomas with respect to organ-specific antigens CDX-2, TTF-1, PAX-8 and GATA-3. An extensive immunohistochemical and molecular analysis of the cohort is summarized in detail elsewhere [14].

The use of immunohistochemistry in typing tumors of uncertain primary origin is routine in surgical pathology in metastatic disease. Accurate tumor classification is crucial for advancing targeted antitumor therapies. Various recommendations and algorithms for antibody panels have been proposed [15, 16], particularly considering the limited tissue available in small biopsy samples, where preservation for molecular examination is crucial. A panel of antibodies is recommended, since the use of a single antibody alone may lead to misleading results [17, 18]. TTF-1, CDX-2, PAX-8 and GATA-3 are the most frequently used antibodies for differential diagnostics [19–21] of adenocarcinomas with an unknown primary origin.

Extrapulmonary small cell carcinomas are extremely rare tumors. Like small cell lung carcinomas, patients with this condition often present with extensive, disseminated disease. However, the primary sites of origin of EP-SCNCs have proved to be an independent prognostic variable in several large cohort studies [1, 22, 23]. This was also supported by our study, where primary tumor sites were an age-independent prognostic marker (p < 0.0001); digestive tract EP-SCNCs displayed decreased survival compared to those originating in genitourinary organs. Moreover, in our previous study of 181 EP-SCNCs, we separately analyzed tumors with genitourinary origin (genitourinary tract and gynecological tract tumors; n = 105) and tumors of the digestive system (gastrointestinal tract, pancreas, and hepatobiliary system; n = 49); patients with genitourinary SCNCs had significantly longer survival than those with digestive system SCNCs (HR = 1.73, 95% CI: 1.19–2.52, p = 0.004) [14].

Since few studies have explored this topic, we investigated the utility of TTF-1, CDX-2, PAX-8 and GATA-3 in differentiating EP-SCNCs based on their primary sites, area. Kaufman et al.²² identified TTF-1 expression in 80% of EP-SCNCs, supporting its potential diagnostic role. According to ESMO guidelines¹⁴, CDX-2 positivity is indicative of a neuroendocrine tumor originating in the gastrointestinal tract or pancreas. However, our findings challenge this assumption, since only 30% of gastrointestinal tumors and 33.3% of pancreatic tumors exhibited CDX-2 positivity, while 11.1% of genitourinary tumors and 6.3% of gynecological tumors also demonstrated CDX-2 expression.

Consistent with the role of PAX-8 as a transcription factor involved in the organogenesis of the thyroid gland, kidney, and Müllerian system, 62.5% of gynecological tumors, 62.5% of head and neck tumors, and 46.6% of genitourinary tumors showed PAX-8 positivity. On the other hand, PAX-8 positivity was also observed in 66.7% of tumors of hepatobiliary origin, 40% of breast tumors, 25% of gastrointestinal tumors, and 20% of pancreatic tumors.

TTF-1 positivity was detected in 60% of breast tumors, 40% of pancreatic tumors, 34.7% of genitourinary tumors, 20% of gastrointestinal tumors, and 12.5% of head and neck tumors, making it the only immunohistochemical marker in our study to reach statistical significance. However, despite its statistical relevance, its practical utility in accurately determining the primary site of EP-SCNC remains limited in routine clinical practice.

However, importantly, TTF-1 positivity is not exclusive to lung tumors. A vast majority of small cell lung carcinomas exhibit TTF-1 positivity [24]; however, TTF-1 positivity in small cell neuroendocrine tumors should not be considered definitive evidence of a lung primary origin, since nearly 26% of the EP-SCNCs in our study were TTF-1 positive.

In a study of Briski et al. [25], clone of TTF-1 antibody proved to play an important role in EP-SCNC staining. 83% EP-SCNC were positive for clone SPT24 (Novocastra), whereas 48% EP-SCNC were positive for 8G7G3/1 (DAKO). The differences in staining between 8G7G3/1 and SPT24 in the nonpulmonary cohort were statistically significant (P < 0.0001). The difference of the clones 8G7G3/1 and SPT24 is discussed in a study of metastatic adenocarcinomas in lungs, where the SPT24 clone seemed to be more sensitive, but less specific for TTF-1 protein [26].

The biological role of TTF-1 in tumorigenesis remains to be clarified, since few studies explored this topic. In a manuscript of Iso H. et al., TTF-1-negative NSCLC exhibited distinct biological characteristics, such as a higher prevalence of certain genetic mutations (e.g., STK11, KEAP1) and an immunosuppressive tumor microenvironment. According to authors, these factors might contribute to the observed resistance to therapies and poorer prognoses of patients with TTF-1-negative NSCLC in their study [27]. 4 and 3 tumors had STK11 and KEAP1 mutation in our study and all of them were TTF-1 negative at the same time [14].

Interestingly, in a study of Iida Y. et al., TTF-1-negative SCLC were different in aspects of neuroendocrine differentiation (negativity of synaptophysin and chromogranin, lower expression of ASCL1) compared to TTF-1-positive SCLC [28]. Concerning EP-SCNC, ASCL1 negative tumors are known to constitute a larger proportion than in SCLC [14].

TTF-1 positivity proved to have a negative prognostic value in our study, which can be partly supported by the above-mentioned study of Iso H. et al. [27]. However, this finding is in contrast with results of a robust meta-analysis conducted by Wang Y. et al., who studied 11 manuscripts comprising 1,786 SCLC patients, where TTF-1 expression indicated improved overall survival (OS) (HR = 0.56, 95% CI: 0.45–0.70; P < 0.001) and progression-free survival (PFS) (HR = 0.41, 95% CI: 0.28–0.62; P < 0.001) [5]. Moreover, TTF-1 positivity proved to have a positive prognostic impact in a meta-analysis performed by Qian H.H. et al., who studied 17 manuscripts comprising 2,235 patients with non-small cell lung carcinoma; TTF-1 overexpression had a favorable impact on survival (HR = 0.49, 95% CI: 0.42–0.55) [29].

Conclusion

Although EP-SCNC has been repeatedly shown to be a heterogeneous disease that is partially responsive to platinum-based chemotherapy, no consensus exists on the optimal second-line therapy in cases of progression [3, 30]. To advance therapeutic strategies requires a deeper understanding of molecular and immune characteristics. However, our study of TTF-1, CDX-2, PAX-8 and GATA-3 immunohistochemistry did not prove to be useful in identifying the primary site of EP-SCNC origin and, in our opinion, should be interpreted with caution. Importantly, TTF-1 positivity should not be regarded as definitive evidence of pulmonary origin in small cell carcinoma. In EP-SCNC, patient age and primary tumor site remain the most robust prognostic indicators, and, notably, TTF-1 expression was identified as an independent adverse prognostic factor in our cohort.

Limitations

The TMA approach, despite its widespread use in research, carries a risk of under- or overestimation of immunohistochemical scoring and may be a limitation due to tumor heterogeneity.

Although our cohort of 138 patients with EP-SCNC is one of the largest in literature, the number of patients in each tumor group is limited, which may constrain the statistical interpretation of results.

Supplementary Information

13000_2026_1753_MOESM1_ESM.xlsx (19.4KB, xlsx)

Supplementary Material 1: Detailed distribution of TTF-1, CDX-2, PAX-8 and GATA-3 expressions in different organs and organ systems.

Acknowledgements

We would like to express our special thanks to Mr. Thomas Secrest, MSc, for language editing services and Alena Poláková, MSc, for her excellent technical assistance.

Abbreviations

EP

SCNC–Extrapulmonary Small Cell Neuroendocrine Carcinoma

TTF-1

1–Thyroid Transcription Factor 1

CDX-2

2–Caudal–related Homeobox 2

PAX-8

8–Paired Box Gene 8

GATA-3

3–GATA–binding protein 3

IHC

Immunohistochemistry

OS

Overall Survival

FFPE

Formalin–Fixed Paraffin–Embedded

TMA

Tissue Microarray

NGS

Next–Generation Sequencing

HR

Hazard Ratio

CI

Confidence Interval

NSCLC

Non–Small Cell Lung Carcinoma

SCLC

Small Cell Lung Carcinoma

PFS

Progression–Free Survival

ASCL1

Achaete–Scute Family Transcription Factor 1

Authors’ contributions

K.P. created the patients´ cohort, performed immunohistochemistry, and prepared the manuscript; R. Matěj designed the study, reviewed the paper, and performed the immunohistochemical analysis; P. Dundr and J. Hrudka reviewed the paper; P.W. was responsible for statistical analysis; J.L., M.Š., P.F., I.S.Z., M.F., H.H. and J.Š. contributed to patient cohort creation.All authors read and approved the paper.

Funding statement

This work was supported by the Ministry of Health of the Czech Republic (project Conceptual Development of Research Organization, General University Hospital, Prague (VFN, 00064165) and Thomayer University Hospital (FTN, 00064190)), the Agency for Health Research of the Czech Republic (project NU22-03-00130), by the European Regional Development Fund (BBMRI_CZ LM2023033), and by the Charles University (projects UNCE 24/MED/018 and Cooperatio Medical Diagnostics and Basic Medical Sciences).

Data availability

All data generated or analyzed during this study are included in the published article and its supplementary information files.

Declarations

Ethics approval consent to participate

This study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of the Institute for Clinical and Experimental Medicine and Thomayer University Hospital No G-21-39.

Consent for publication

All authors read and approved the paper for publication.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

  • 1.Dasari A, Mehta K, Byers LA, Sorbye H, Yao JC. Comparative study of lung and extrapulmonary poorly differentiated neuroendocrine carcinomas: A SEER database analysis of 162,983 cases. Cancer. 2018;124(4):807–15. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Frazier SR, Kaplan PA, Loy TS. The pathology of extrapulmonary small cell carcinoma. Semin Oncol. 2007;34(1):30–8. [DOI] [PubMed] [Google Scholar]
  • 3.Stelwagen J, de Vries EGE, Walenkamp AME. Current treatment strategies and future directions for extrapulmonary neuroendocrine carcinomas: A review. JAMA Oncol. 2021;7(5):759–70. [DOI] [PubMed] [Google Scholar]
  • 4.Badia-Ramentol J, Gimeno-Valiente F, Durendez E, Martinez-Ciarpaglini C, Linares J, Iglesias M, Cervantes A, Calon A, Tarazona N. The prognostic potential of CDX2 in colorectal cancer: harmonizing biology and clinical practice. Cancer Treat Rev. 2023;121:102643. [DOI] [PubMed] [Google Scholar]
  • 5.Wang Y, Wu Y, Li J, Li J, Che G. Clinicopathological and prognostic significance of thyroid transcription factor-1 expression in small cell lung cancer: A systemic review and meta-analysis. Pathol Res Pract. 2019;215(12):152706. [DOI] [PubMed] [Google Scholar]
  • 6.Guan L, Zhao X, Tang L, Chen J, Zhao J, Guo M, Chen C, Zhou Y, Xu L. Thyroid transcription Factor-1: Structure, Expression, function and its relationship with disease. Biomed Res Int. 2021;2021:9957209. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Zhou Q, Li H, Cheng Y, Ma X, Tang S, Tang C. Pax-8: molecular biology, pathophysiology, and potential pathogenesis. BioFactors. 2024;50(3):408–21. [DOI] [PubMed] [Google Scholar]
  • 8.Ordonez NG. Value of PAX 8 immunostaining in tumor diagnosis: a review and update. Adv Anat Pathol. 2012;19(3):140–51. [DOI] [PubMed] [Google Scholar]
  • 9.Miettinen M, McCue PA, Sarlomo-Rikala M, Rys J, Czapiewski P, Wazny K, Langfort R, Waloszczyk P, Biernat W, Lasota J, Wang Z. GATA3: a multispecific but potentially useful marker in surgical pathology: a systematic analysis of 2500 epithelial and nonepithelial tumors. Am J Surg Pathol. 2014;38(1):13–22. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Posit team. RStudio: Integrated Development Environment for R. Posit Software, PBC, Boston. MA. 2026. http://www.posit.co/.
  • 11.Therneau T (2026). A Package for Survival Analysis in R. R package version 3.7-0
  • 12.Denz R, Klaaßen-Mielke R, Timmesfeld N. A comparison of different methods to adjust survival curves for confounders. Stat Med. 2023;42(10):1461–79. 10.1002/sim.9681. [DOI] [PubMed]
  • 13.Koo J, Mertens RB, Mirocha JM, Wang HL, Dhall D. Value of islet 1 and PAX8 in identifying metastatic neuroendocrine tumors of pancreatic origin. Mod Pathol. 2012;25(6):893–901. [DOI] [PubMed] [Google Scholar]
  • 14.Pavlickova K, Hojny J, Waldauf P, Svajdler M, Dundr P, Fabian P, Krkavcova E, Dvorak J, Michalkova R, Zambo IS, Hajkova N, Flidrova M, Laco J, Hornychova H, Delongova P, Skarda J, Hrudka J. Matej, molecular and immunohistochemical classification of extrapulmonary small cell neuroendocrine carcinomas: A study of 181 cases. Lab Invest. 2025;105(4):104093. [DOI] [PubMed] [Google Scholar]
  • 15.Conner JR, Hornick JL. Metastatic carcinoma of unknown primary: diagnostic approach using immunohistochemistry. Adv Anat Pathol. 2015;22(3):149–67. [DOI] [PubMed] [Google Scholar]
  • 16.Kramer A, Bochtler T, Pauli C, Baciarello G, Delorme S, Hemminki K, Mileshkin L, Moch H, Oien K, Olivier T, Patrikidou A, Wasan H, Zarkavelis G, Pentheroudakis G, Fizazi K. E.G.C.E.a. clinicalguidelines@esmo.org, cancer of unknown primary: ESMO clinical practice guideline for diagnosis, treatment and follow-up. Ann Oncol. 2023;34(3):228–46. [DOI] [PubMed] [Google Scholar]
  • 17.Choi SM, Furth EE, Zhang PJ. Unexpected TTF-1 positivity in a subset of gastric adenocarcinomas. Appl Immunohistochem Mol Morphol. 2016;24(8):603–7. [DOI] [PubMed] [Google Scholar]
  • 18.Surrey LF, Frank R, Zhang PJ, Furth EE. TTF-1 and Napsin-A are expressed in a subset of cholangiocarcinomas arising from the gallbladder and hepatic ducts: continued caveats for utilization of immunohistochemistry panels. Am J Surg Pathol. 2014;38(2):224–7. [DOI] [PubMed] [Google Scholar]
  • 19.Laury AR, Perets R, Piao H, Krane JF, Barletta JA, French C, Chirieac LR, Lis R, Loda M, Hornick JL, Drapkin R, Hirsch MS. A comprehensive analysis of PAX8 expression in human epithelial tumors. Am J Surg Pathol. 2011;35(6):816–26. [DOI] [PubMed] [Google Scholar]
  • 20.Erickson LA, Papouchado B, Dimashkieh H, Zhang S, Nakamura N, Lloyd RV. Cdx2 as a marker for neuroendocrine tumors of unknown primary sites. Endocr Pathol. 2004;15(3):247–52. [DOI] [PubMed] [Google Scholar]
  • 21.Werling RW, Yaziji H, Bacchi CE, Gown AM. CDX2, a highly sensitive and specific marker of adenocarcinomas of intestinal origin: an immunohistochemical survey of 476 primary and metastatic carcinomas. Am J Surg Pathol. 2003;27(3):303–10. [DOI] [PubMed] [Google Scholar]
  • 22.Sorbye H, Welin S, Langer SW, Vestermark LW, Holt N, Osterlund P, Dueland S, Hofsli E, Guren MG, Ohrling K, Birkemeyer E, Thiis-Evensen E, Biagini M, Gronbaek H, Soveri LM, Olsen IH, Federspiel B, Assmus J, Janson ET, Knigge U. Predictive and prognostic factors for treatment and survival in 305 patients with advanced Gastrointestinal neuroendocrine carcinoma (WHO G3): the NORDIC NEC study. Ann Oncol. 2013;24(1):152–60. [DOI] [PubMed] [Google Scholar]
  • 23.Ulanja MB, Beutler BD, Antwi-Amoabeng D, Governor SB, Rahman GA, Djankpa FT, Alese OB. Prognostic factors and survival in Gastrointestinal extrapulmonary small cell carcinoma: A retrospective cohort study. Ann Surg Oncol. 2022;29(13):8250–60. [DOI] [PubMed] [Google Scholar]
  • 24.Wang B, Feng N, Shi X, Qi Q, Chi X, Song T, Li H. [Analysis of correlation between TTF-1 and sensitivity to First-line chemotherapy and prognosis in patients with small cell lung Cancer]. Zhongguo Fei Ai Za Zhi. 2020;23(7):547–53. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Briski LM, Aron M, Epstein JI, Russell DH, Assarzadegan N, Delma KS, O’Dell H, Rodriguez E, Montgomery EA, Kryvenko ON. Patterns of immunoreactivity with TTF-1 antibodies 8G7G3/1 and SPT24 suggest distinct immunoprofiles between most pulmonary and nonpulmonary small cell carcinomas. Int J Surg Pathol. 2024;32(2):230–8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Comperat E, Zhang F, Perrotin C, Molina T, Magdeleinat P, Marmey B, Regnard JF, Audouin J. Camilleri-Broet, variable sensitivity and specificity of TTF-1 antibodies in lung metastatic adenocarcinoma of colorectal origin. Mod Pathol. 2005;18(10):1371–6. [DOI] [PubMed] [Google Scholar]
  • 27.Iso H, Hisakane K, Mikami E, Suzuki T, Matsuki S, Atsumi K, Nagata K, Seike M, Hirose T. Thyroid transcription factor-1 (TTF-1) expression and the efficacy of combination therapy with immune checkpoint inhibitors and cytotoxic chemotherapy in non-squamous non-small cell lung cancer. Transl Lung Cancer Res. 2023;12(9):1850–61. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Iida NTY, Nakanishi Y, Nishimaki H, Nakagawa Y, Shimizu T, Mizumura K, Maruoka S, Gon Y, Masuda S, Hashimoto S. P2.15-015 Negativity for Thyroid Transcription Factor 1 Was Correlated with Less Neuroendocrine Differentiation in Small Cell Lung Cancers, IASLC 18th World Conference on Lung Cancer, Journal of Thoracic Oncology, 2017, pp. Pages S2188-S2189.
  • 29.Qian HH, Xu TS, Cai XQ, Ji TL, Guo HX. Prognostic value of TTF-1 expression in patients with non-small cell lung cancer: A meta-analysis. Clin Chim Acta. 2015;451:208–14. (Pt B). [DOI] [PubMed] [Google Scholar]
  • 30.McNamara MG, Frizziero M, Jacobs T, Lamarca A, Hubner RA, Valle JW, Amir E. Second-line treatment in patients with advanced extra-pulmonary poorly differentiated neuroendocrine carcinoma: a systematic review and meta-analysis. Ther Adv Med Oncol. 2020;12:1758835920915299. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

13000_2026_1753_MOESM1_ESM.xlsx (19.4KB, xlsx)

Supplementary Material 1: Detailed distribution of TTF-1, CDX-2, PAX-8 and GATA-3 expressions in different organs and organ systems.

Data Availability Statement

All data generated or analyzed during this study are included in the published article and its supplementary information files.

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