Differential expression of various clones of estrogen receptor in cell block preparation of lung adenocarcinoma

Background: Women treated for breast cancer are at increased risk of developing pulmonary nodules which could represent new primary lung carcinomas or metastatic breast carcinoma. The FNA biopsy is frequently the first diagnostic choice in determining the primary site of the tumor. Estrogen receptor (ER) positivity in diagnostic tissue is generally used to favor breast over lung primary. However, the recent studies have shown a wide range of ER antibody cross reactivity with lung adenocarcinoma. We studied the frequency of ER expression in cytology samples of lung adenocarcinoma using antibodies to three different ER clones. Methods: Cytology cell block preparations, including 22 lung FNAs and 19 malignant pleural effusions (PE) from 41 patients, with clinically documented primary lung adenocarcinomas were selected for this study. All cases were stained with monoclonal antibodies to ER clones 6F11 and 1D5. Twenty nine cases with remaining available material (15 FNA and 14 PE) were stained with a third antibody to ER clone SP1. The extent of ER nuclear staining was scored as 3+ (50%–100% of tumor cells), 2+ (11%–49%), and 1+ (≤10%). Results: Positivity for ER-6F11 clone was present in 4 of 22 lung FNAs (18.2%, 2+ staining). Two of the four 6F11 positive FNAs also co-expressed ER-1D5 (9.1%, 2+ staining). No immunoreactivity was observed for ER clones 6F11 and 1D5 in all 19 malignant PEs. In addition, none of the remaining 15 FNAs and 14 PEs showed immunoreactivity for ER-SP1 clone. Conclusions: A small subset of pulmonary adenocarcinomas shows immunoreactivity for ER clones 6F11 and 1D5 in FNA samples (18.2% and 9.1%, respectively). The absence of immunoreactivity for ER-SP1 clone indicates higher specificity of this clone in non-breast tissue. The differential diagnostic value of all ER clones in malignant PEs appears to be secure. Larger studies are necessary to validate this observation.