[380] Differential Expression of Two Different TTF-1 and Napsin A Double Stain Antibodies: Utility in Detecting Lung Adenocarcinomas

Hunter Johnson, Nazneen Fatima, Cynthia Cohen, David Duncan, Momin T Siddiqui. Emory University Hospital, Atlanta, GA; Leica Biosystems Newcastle Ltd, Newcastle upon Tyne, United Kingdom

Background: Immunohistochemistry (IHC) for thyroid transcription factor -1 (TTF-1) and Napsin A are used to confirm the diagnosis of lung adenocarcinoma (ADC). This double stain has been shown to be useful in the diagnosis of ADC in cell blocks (CB) from fine needle aspirates (FNAs). An attempt to elucidate any statistical differences between the double staining patterns between comparable vendor antibodies (Leica and Dako) was addressed.
Design: 35 FNA cell blocks of lung ADC and 24 of lung squamous cell carcinoma (SqCCA),were selected. Double-staining IHC was performed using Leica and Dako antibodies for TTF-1 and Leica antibodies for Napsin A, with TTF-1 as a brown nuclear stain and Napsin A as a red cytoplasmic stain. The expression results were identified and compared. FISH assay was performed on SqCCAs with aberrant expression of TTF-1.
Results: Twenty six of 35 (74%) lung ADCs were positive for both TTF-1 and Napsin A using the Dako TTF-1 antibody. Two ADCs expressed TTF-1 only; 4 cases expressed Napsin A only. One of 23 SqCCAs was positive for both using Dako, with 1 additional SqCCA being positive for TTF-1 only. This differs significantly from the Leica staining results, in which 3 of 24 SqCCAs expressed double staining and 6 of 24 expressed TTF-1 only.

Staining Results

	ADC	SqCCA
Leica
TTF-1/Napsin A	26/35 (74%)	3/24 (13%)
TTF-1 total positive	28/35 (80)	9/24 (38)
Napsin A total positive	29/35 (83)	3/24 (13)
Dako
TTF-1/Napsin A	26/35 (74)	1/23 (4)
TTF-1 total positive	28/35 (80)	2/23 (7)
Napsin A total positive	30/35 (86)	1/23 (4)

Statistical Analysis

	Sensitivity	Specificity	PPV	NPV	Accuracy
Leica
TTF-1/ Napsin A	74%	87	89	70	79
TTF-1 (total)	80	62	75	68	72
Napsin A (total)	82	87	90	77	84
Dako
TTF-1/ Napsin A	74	96	96	71	83
TTF-1 (total)	80	91	93	75	84
Napsin A (total)	86	96	97	81	90

PPV, positive predictive value; NPV, negative predictive value

Two TTF-1 positive SqCCAs showed low level amplification by FISH assay not seen in the TTF-1 negative control SqCCAs. With Leica antibodies, 28 of 35 (80%) ADC were both positive, 2 were TTF-1 only positive, and 3 were Napsin A only positive.
Conclusions: The double IHC stain for TTF-1/Napsin A is useful in the diagnosis of lung ADC. The use of Dako TTF-1 yielded the better results, having the same sensitivity as Leica, but with a higher specificity. Dako antibodies express less staining of SqCCAs; this may be due to increased sensitivity of the Leica antibody, making it less useful in differentiating ADC from SqCCA.
Category: Cytopathology

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 69, Monday Morning