Immunofluorescent and molecular characterization of effusion tumor cells reveal cancer site‐of‐origin and disease‐driving mutations

Background Effective cancer treatment relies on precision diagnostics. In cytology, an accurate diagnosis facilitates the determination of proper therapeutics for patients with cancer. Previously, the authors developed a multiplexed immunofluorescent panel to detect epithelial malignancies from pleural effusion specimens. Their assay reliably distinguished effusion tumor cells (ETCs) from nonmalignant cells; however, it lacked the capacity to reveal specific cancer origin information. Furthermore, DNA profiling of ETCs revealed some, but not all, cancer‐driver mutations. Methods The authors developed a new multiplex immunofluorescent panel that detected both malignancy and pulmonary origin by incorporating the thyroid transcription factor‐1 (TTF‐1) biomarker. Evaluation for TTF‐1–positive ETCs (T‐ETCs) was performed on 12 patient samples. T‐ETCs and parallel ETCs from selected patients were collected and subjected to DNA profiling to identify pathogenic mutations. All samples were obtained with Institutional Review Board approval. Results Malignancy was detected in all samples. T‐ETCs were identified in 9 of 10 patients who had clinically reported TTF‐1 positivity (90% sensitivity and 100% specificity). Furthermore, DNA profiling of as few as five T‐ETCs identified pathogenic mutations with equal or greater sensitivity compared with profiling of ETCs, both of which showed high concordance with clinical findings. Conclusions The findings suggest that the immunofluorescent and molecular characterization of tumor cells from pleural effusion specimens can provide reliable diagnostic information, even with very few cells. The integration of site‐specific biomarkers like TTF‐1 into ETC analysis may facilitate better refined diagnosis and improve patient care. The lung adenocarcinoma‐specific biomarker TTF‐1 was incorporated into an epithelial malignancy detection panel to determine the cancer origin of effusion tumor cells identified from pleural effusion specimens. Molecular profiling of five TTF‐1–positive effusion tumor cells revealed pathogenic mutations with great sensitivity compared with clinical testing.