The Application and Diagnostic Utility of Immunocytochemistry on Direct Smears in the Subclassification of Non-Small Cell Lung Carcinoma.
Michael H Roh, Lindsay Schmidt, Jeremiah Placido, Sara Farmen, Kristina L Fields, Stewart M Knoepp. University of Michigan Medical School, Ann Arbor
Background: Cytologic specimens are commonly obtained to establish a tissue diagnosis in patients with non-small cell lung cancer (NSCLC). Not uncommonly, though, cell blocks traditionally used for ancillary studies such as immunocytochemistry (ICC) are sparsely cellular or acellular. Given recent advances in chemotherapy for the treatment of specific subtypes of NSCLC, the importance of subclassifying NSCLC is becoming increasingly paramount. The two most common subtypes of NSCLC are adenocarcinoma (ADC) and squamous cell carcinoma (SQC). Recently, Napsin A expression has been reported in a high percentage of ADC but not SQC. Furthermore, a TTF-1(+) immunophenotype favors ADC over SQC. In contrast, strong p63 immunoreactivity favors SQC over ADC. In our ongoing study, we seek to investigate the diagnostic utility of ICC for Napsin A, TTF-1, and p63 on direct smears (DS) of NSCLC.
Design: First, the performance of Napsin A immunohistochemistry (IHC) was verified on a tissue microarray (TMA) composed of 117 lung ADCs. Next, ICC for Napsin A along with TTF-1 and p63 was performed on air-dried, unstained DS after brief formalin fixation and antigen retrieval in 15 cases. Surgically resected tumor tissue was available in nine of the 15 cases. In these cases, IHC for all three markers was performed, in parallel, using slides prepared from formalin-fixed, paraffin-embedded (FFPE) tissue blocks.
Results: First, the majority of lung ADCs on the TMA (85 of 117; 73%) were immunoreactive for Napsin A. Next, ICC for Napsin A, TTF-1, and p63 was applied to DS in 15 cases (10 ADCs and 5 SQCs). The results of the ICC along with IHC using FFPE tissue are summarized in Table 1.
|Case||Diagnosis||Napsin A (DS)||TTF-1 (DS)||p63 (DS)||Napsin A (FFPE)||TTF-1 (FFPE)||p63 (FFPE)|