Thyroid transcription factor-1, TTF-1, Nkx2.1, thyroid-specific enhancer-binding protein

A 38 kD homeodomain-containing nuclear transcription protein of the Nkx2 gene family. It acts as a master regulator gene, binding to the promoters for surfactant apoproteins A, B and C, Clara cell antigen and T1a¹⁸. During embryogenesis, it is first expressed at the emergence of the laryngeotracheal diverticulum and is localised to the bronchial epithelium. Once the bronchial tree has developed, expression shifts to the peripheral airway epithelium, a pattern retained throughout life¹⁸.

The commercially available monoclonal antibody 8G7G3/1 can be used on formalin-fixed, paraffin-embedded tissues: this antibody has been used in most studies of TTF-1. There is a second monoclonal antibody, SPT24, which appears to have greater sensitivity, at the expense of loss of specificity: see comparison of monoclonal antibodies. The monoclonal antibodies probably have greater sensitivity than the polyclonal antibody used in some early studies.

Staining for TTF-1 is nuclear. Cases should be regarded as positive even if the nuclear staining is only focally present in the tumour (i.e. 1% to 10% of the tumour cells)²³. In up to 10% of TTF-1-positive lung adenocarcinomas, staining is present in less than 10% of the tumour cells^24,25. Even this focal staining is not encountered in adenocarcinomas of non-pulmonary and non-thyroid origin.

A rapid technique has been developed for use with intra-operative frozen sections³⁷.

Cytoplasmic Immunoreactivity for TTF-1 has been reported as useful in the diagnosis of hepatocellular carcinoma.

Immunohistochemical expression

TTF-1 is expressed in various normal tissues: follicular cells of the thyroid, type II epithelial cells of the alveoli⁴ and a subset of bronchiolar cells⁴, the anterior pituitary, parathyroid gland, parafollicular C-cells and in certain regions of the brain.

Tumours:

Lung	adenocarcinoma	77% (322/4445, 70/976, 23/2612, 42/47 (8/8 primary and 34/39 metastatic, using cell blocks from FNA)15, 12/1516, 14/1719, 37/4320, 24/3522, 11/11 (brain metastases)23, 30/40(using clone 8G7G3/1)25, 37/50 (8 case >75% of cells stained, 15 cases 50-75% of cells, 10 cases 25-50% of cells, 4 cases 1-25% of cells)26, 46/6418, 110/128 (96/128 pulmonary adenocarcinomas showed high levels of TTF-1 expression; 14 more showed only weak expression. This study also broke down the results by tumour subtype)31), 37/5035, 51/75 (using tissue microarray)38, 27/30 (strong in 14/15 well differentiated, 7/8 moderately differentiated: th negative case was a mucinous cystadenocarcinoma, and 6/7 poorly differentiated.39, 220/231 (169/176 solitary adenocarcinomas, 34/34 multifocal carcinomas, 1/1 signet ring cell carcinoma, 16/20 mucinous carcinomas: using monoclonal 8G7G3/1)45, 42/50(in addition, four cases showed cytoplasmic staining, using clone 8G7G3/1)46, 13/16(cell blocks from cases with metastatic adenocarcinoma to serous cavities, using clone 8G7G3/1)47, 15/17(cell blocks from cases with metastatic adenocarcinoma to serous cavities, using clone 8G7G3/1)48, 8/13(using monoclonal 8G7G3/1)50
	bronchoalveolar carcinoma	25/292, 25/28 (20/20 non-mucinous or mixed, 5/8 mucinous)20, 34/50 (30/32 non-mucinous and 4/18 mucinous)35, 8/16 (1 of 6 mucinous, 7/10 non-mucinous)36, 11/14 (10/10 non-mucinous, 1/1 mixed and 0/3 pure mucinous)39, 42/67 (36/48 non-mucinous, 0/12 mucinous, 6/7 mixed; in 5 cases, staining was restricted to the non-mucinous component)42, 23/23 (non-mucinous bronchoalveolar carcinomas: using monoclonal 8G7G3/1)45
	small cell carcinoma	88% (170/1855,7,8, 43/529, 1/415,11/1218, 6/7 (brain metastases)23, 47/5532, 24/3039, 3/540), 20/2141, 19/36 (using monoclonal 8G7G3/1)45
	squamous cell carcinoma	7% (20/2015, 6/1196, 0/1212, 1/7 (using cell blocks from FNA)15, 0/3 (brain metastases)23), 0/1030, 0/2931, 9/43 (using tissue microarray)38, 1/30 (2% of nuclei in one case)39, 4/99 (using monoclonal 8G7G3/1)45
	basaloid squamous cell carcinoma	0/2812
	basaloid carcinoma	0/2812
	adenosquamous carcinoma	1/3 (only glandular component positive)39
	large cell carcinoma	6/625, 0/26, 15/19 (brain metastases)23, 3/1030, 0/131, 0/2 (using tissue microarray)38, 4/2539
	large cell neuroendocrine carcinoma	46% (2/47, 6/85, 18/4412), 2/231, 31/6432, 6/1039, 6/840, 6/841
	pleomorphic carcinoma	~55%, 0/23(using monoclonal 8G7G3/1)45
	lymphoepithelioma-like carcinoma	0/25(using monoclonal 8G7G3/1)45
	typical carcinoid	22/68 (The low rate of positivity may be due to the use of polyclonal antibody.)5,7, 16/1710, 11/1613, 1/131, 0/27(using monoclonal antibody , clone 8G7G3/1, Microm, Francheville, France, with heat-induced antigen retrieval)32†, 6/2339, 18/5141, 0/8(using monoclonal 8G7G3/1)45
	atypical carcinoid	11/125,7, 3/310, 0/23 (using monoclonal antibody, clone 8G7G3/1, Microm, Francheville, France, with heat-induced antigen retrieval)32†, 9/941, 0/3(using monoclonal 8G7G3/1)45
	metastatic pulmonary carcinoid	8/1810
	neuroendocrine hyperplasia and tumourlets	0/15 (neuroendocrine hyperplasia)32, 0/23 (tumourlets)32
	sclerosing haemangioma	36/373, 16/1614, 39/44(using monoclonal 8G7G3/1)45
	pulmonary papillary adenoma	1/127
Extra-pulmonary adenocarcinoma (excluding thyroid)		3%
Extra-pulmonary small cell carcinoma (excluding skin)		36% (42/114), various sites
Extra-pulmonary squamous cell carcinoma		0/3 (brain metastases from tongue, pharynx and oesophagus)23
Extra-pulmonary large cell neuroendocrine carcinoma		1/4 (various sites)7
Extra-pulmonary carcinoid		1% (1/207, 0/5010, 0/4911, 1/5813)
Extra-pulmonary endocrine tumours	parathyroid adenoma	0/1010
	pituitary adenoma	0/2010
	pancreatic endocrine tumour	0/1010
	adrenocortical carcinoma	0/1 (brain metastasis)23
	phaeochromocytoma	0/510
Malignant mesothelioma		0% (0/952, 0/244, 0/14 [using cell blocks from FNA]15, 0/4122, 0/60 [all epithelioid mesotheliomas])26, 0/4(using a polyclonal antibody)49, 0/50(using clone 8G7G3/1)25
Thyroid	adenoma	13/155, 5/510, 10/12 (5/6 follicular and 5/6 oncocytic adenomas)28
	follicular carcinoma	14/145, 5/510, 4/428, 3/3(using clone 8G7G3/1)25
	papillary carcinoma	27/285, 5/510, 8/828, 7/7(using clone 8G7G3/1)25
	Hurtle cell carcinoma	1/55, 2/628
	Insular carcinoma	5/55
	medullary carcinoma	15/165,7, 10/1010, 1/228
	poorly differentiated carcinoma	0/1 (brain metastasis)23, 6/728
	anaplastic carcinoma	2/3517, 0/85, 2/510, 1/4 (all negative for thyroglobulin)28
Thymic neoplasms		0/201, 0/310, 0/57 (35 thymomas and 22 thymic carcinomas)29, 0/30 (14 thymomas and 6 thymic carcinomas)30
testicular choriocarcinoma		0/5 (10 normal placentas were also negative)21
Melanoma		0/1 [using cell blocks from FNA]15
Merkel cell carcinoma of skin		0/375,7, 0/239

Among primary pulmonary adenocarcinomas, there is a higher rate of positivity in tumours thought to be derived from the terminal respiratory unit (TRU, in the WHO classification these are most non-mucinous bronchioloalveolar, mixed bronchioloalveolar and acinar subtypes and some papillary subtypes); 42/48 with TRU morphology were positive, as against 4/16 with non-TRU morphology¹⁸. In one paper, immunoreactivity in adenocarcinomas is more common in females (27/31 positive) than males (19/33 positive) and in nonsmokers (26/31 positive) than in smokers (20/33 positive), in p53-negative tumours and in retinoblastoma-positive tumours¹⁸. However, another reports that no associations were noted with gender⁶. A comparison of primary tumours and their metastases showed no tendency to loss of staining during dissemination¹⁸.

Two studies showed postivity for TTF-1 in conventional pulmonary adenocarcinomas to be a significant independent predictor of survival^35,38. A second study Another found a tendency (p=0.096) to an association between TTF-1 positivity and better survival³⁴, along with a negative correlation with Ki-67 proliferative activity (p=0.003): another found no association of TTF-1 positivity with survival³¹.

When large cell neuroendocrine carcinoma of the lung is a component of a combined tumour, it adopts the TTF-1 reactivity of the other component, positive where it is small cell carcinoma and with some adenocarcinomas, negative where it is squamous cell carcinoma^12,32. In one of these studies, three combined small cell / squamous cell carcinomas showed negativity of both components³².

†The inconsistent results in carcinoids, typical and atypical, may be due to the use of polyclonal antibodies in early studies, misinterpretation of granular cytoplasmic staining that overlaps the nucleus, and the misclassification of large cell neuroendocine carcinomas at atypical carcinoids prior to the 1999 WHO classification³².

Diagnostic utility

	positive predictive value	negative predictive value
To differentiated pulmonary from extrapulmonary adenocarcinoma (best used in combination with cytokeratins 7 and 20)	99%	70%
To show tumour is an extra-pulmonary small cell carcinoma, not a Merkel cell carcinoma	100%	76%
To show carcinoid is of pulmonary origin	97%	30%

If a small cell carcinoma is negative for TTF-1, it is less likely to be of pulmonary origin, but positivity for TTF-1 does not demonstrate that it is on pulmonary origin.

Differentiation of adenocarcinoma from mesothelioma⁴³. A systematic review of five studies (consisting of 366 pulmonary adenocarcinomas and 240 epithelioid mesotheliomas) reported sensitivities and specificities of TTF-1 for pulmonary adenocarcinoma of 72% and 100%.⁵¹.

Differentiation of small cell carcinoma from poorly differentiated squamous cell carcinoma of lung.

• Cytoplasmic Immunoreactivity for TTF-1 has been reported as useful in the diagnosis of hepatocellular carcinoma

• Identifying thryroid neoplasms⁴³. Note that rarely anaplastic carcinoma of the thyroid may be positive for TTF-1 but negative for thyroglobulin²⁸.

References

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²A Khoor et al. Utility of surfactant protein B precursor and thyroid transcription factor 1 in differentiating adenocarcinoma of the lung from malignant mesothelioma. Human Pathology 1999;30:695-700.

³M Devousassoux-Shisheboran et al. A clinicopathological study of 100 cases of pulmonary sclerosing hemangioma with immunohistochemical studies. Am J Surg Pathol 2000; 24: 906-916.

⁴Di Loreto C et al. TTF-1 protein expression in pleural malignant mesotheliomas and adenocarcinomas of the lung. Cancer letters 1998;124:73-78.

⁵Ordonez NG. Thyroid transcription factor-1 is a marker of lung and thyroid carcinomas. Advances in Anatomic Pathology 2000; 7(2): 123-127.

⁶Pelosi G et al. Immunoreactivity for thyroid transcription factor-1 in stage I non-small cell carcinomas of the lung. Am J Surg Pathol 2001;25:363-372.

⁷Kaufmann O & Dietel M. Expression of thyroid transcription factor-1 in pulmonary and extrapulmonary small cell carcinomas and other neuroendocrine carcinomas of various primary sites. Histopathology 2000; 36: 415-420.

⁸Ordonez NG. Value of thyroid transcription factor-1 immunostaining in distinguishing small cell lung carcinomas from other small cell carcinomas. Am J Surg Pathol 2000;24:1217-1223.

⁹Cheuk W et al. Immunostaining for thyroid transcription factor-1 and cytokeratin 20 aids in the distinction of small cell carcinoma from Merkel cell carcinoma, but not pulmonary from extrapulmonary small cell carcinoma. Arch Pathol Lab Med 2001;125:228-231.

¹⁰Oliviera AM et al. Thyroid transcription factor-1 distinguishes metastatic pulmonary from well-differentiated neuroendocrine tumors of other sites. Am J Surg Pathol 2001;25:815-819.

¹¹Agoff, S. N., Lamps, L. W., Philip, A. T., Amin, M. B., Schmidt, R. A., True, L. D., Folpe, A. L. Thyroid transcription factor-1 is expressed in extrapulmonary small cell carcinomas but not in other extrapulmonary neuroendocrine tumours. Mod Pathol 2000;13:238-242.

¹²Sturm, N., Lantuejoul, S., Laverriere, M. H., Papotti, M., Brichon, P. Y., Brambilla, C., Brambilla, E. Thyroid transcription factor 1 and cytokeratins 1, 5, 10, 14 (34betaE12) expression in basaloid and large-cell neuroendocrine carcinomas of the lung. Hum Pathol 2001;32:918-925.

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This page last revised 16.2.2006.

©SMUHT/PW Bishop