1228P A circulating tumor cell (CTC) based assay for diagnostic immunocytochemistry profiling of lung cancer

We present a unique immunocytochemistry-based organ-specific antibody profiling assay of CTCs in suspected lung tumors (TruBlood® Lung) for non-invasive diagnosis and histological subtyping and its utility in patients unable to undergo physical biopsies. In a prospective blinded study, blood samples from suspected lung cancer patients (n= 99) were profiled for detection of CTCs. Along with EPCAM/CK/CD45, organ-specific antibody profiling with TTF1, CK7, Napsin A, CD45, p40, Synaptophysin, and Chromogranin was performed to detect lung adenocarcinoma, squamous cell carcinoma and neuroendocrine tumors (TruBlood® Lung). After unblinding, the performance was compared with histopathology of the corresponding tissue samples. Concordance analysis could be performed in ninety-three patients. Tissue HPE was inconclusive in 4 patients and CTC assay (TruBlood® Lung) could not be performed in 4 patients. The concordance rate between cancer diagnosis by the CTC assay and histopathology was 97.8% (91/93). Among cases identified to be positive for lung cancer on CTC assay (n=91), HPE subtyping of lung cancer could be performed in 83.5% of the cases (76/91). The CTC assay was able to detect presence of cancer but unable to assign a histological subtype (subtype indeterminate) in 16.4% of the cases (15/91). Among cases that were able to be subtyped by CTC assay, the concordance rate with HPE diagnosis was 93.4% (71/76), with concordant subtyping in 76.3% of the total evaluable cohort (71/93). Discordance with histological subtyping was seen in 6.5% (5/76) cases, with CTC assay failing to identify adeno-squamous (n=3), small cell (n=1) and squamous cell carcinoma (n=1) subtypes. Interestingly, in five cases of poorly differentiated carcinomas where conclusive histological subtyping was not possible on tissue HPE examination, CTC assay profiling was able to assign a subtype. Our results demonstrate sensitivity of this CTC assay (TruBlood® Lung) to provide concordant HPE subtyping in 76.3% of the total evaluable cohort (71/93) and in 93.4% (71/76) of the cases subtyped by CTC assay. Thus, this assay can be useful in patients unable to undergo tissue sampling, to establish a diagnosis and conclude histopathological subtype.