Thymidylate synthetase (TS) immunohistochemistry (IHC): Feasibility in a routine clinical setting for patients receiving treatment with pemetrexed for advanced nonsquamous NSCLC

TPS293 Background: Nonsquamous (NS-) NSCLC is a predictive factor for response to pemetrexed (pem). Laboratory evidence suggests that this differential outcome may be related to low TS mRNA expression in NS-NSCLC. In this exploratory phase II trial the primary objective ( PO) is to test prospectively, the correlation between TS protein expression (TSPE) and progression free survival (PFS). This abstract reports the TS assay (TSA) protocol to measure TSPE using IHC. Methods: An open-label, single-arm, multicentric study (with appropriate UK approvals) was undertaken to test the PO in eligible patients (n=68) receiving pem/cisplatin induction followed by maintenance pem until tumour progression (PD). Key eligibility criteria included ECOG PS 0-1, histological diagnosis of stage IIIB/IV NS-NSCLC, and informed consent. The TSA protocol for this study was designed on a validated procedure developed by study sponsors. Diagnostic slides and FFPE blocks are centrally collected for diagnostic verification and TS s...