TS Expression Could Guide Treatment in Nonsquamous NSCLC

“The combination of pemetrexed and cisplatin was superior to gemcitabine and cisplatin only in those non-squamous non–small-cell lung cancer (NSCLC) patients who were negative for the enzyme thymidylate synthase (TS), suggesting it could be used as a predictive marker to guide treatment.

“Previous research has shown that pemetrexed/cisplatin offers superior survival in nonsquamous NSCLC, while gemcitabine/cisplatin was better in squamous NSCLC. “A plausible mechanism for the histotype-dependent efficacy of pemetrexed-based chemotherapy can be explained by the presence of different levels of TS according to histologic types, with adenocarcinoma of lung cancer exhibiting a lower TS protein expression level than squamous cell carcinoma or neuroendocrine carcinoma,” wrote study authors led by Myung-Ju Ahn, MD, PhD, of Sungkyunkwan University School of Medicine in Seoul.

“TS is involved in de novo DNA synthesis, and inhibiting the enzyme leads to arrested cell proliferation; pemetrexed’s antitumor effects arise from inhibition of TS. The new study’s results were published online ahead of print in the Journal of Clinical Oncology.”


Thymidylate Synthase Predicts Response to Chemo in NSCLC

The gist: Scientists have found that measuring a patient’s levels of a protein called thymidylate synthase (TS) could predict how well different kinds of chemotherapy might work for treating non-small cell lung cancer (NSCLC). Specifically, patients with low-levels of TS benefitted more from treatment with cisplatin plus pemetrexed than with cisplatin plus gemcitabine.

“A new phase II study suggests that expression of the enzyme thymidylate synthase (TS) can be used as a predictive marker for patients with non–small-cell lung cancer undergoing chemotherapy. Benefits of cisplatin plus pemetrexed over cisplatin plus gemcitabine were more pronounced in TS-negative patients than in TS-positive patients.

“ ‘Thymidylate synthase,’ said Myung-Ju Ahn, MD, of Sungkyunkwan University School of Medicine in Seoul, in a press release, ‘is targeted by pemetrexed, which is the most widely used chemotherapeutic regimen in the treatment of non-squamous NSCLC.’ Previous work has shown that the cisplatin/pemetrexed combination is superior to cisplatin/gemcitabine in non-squamous NSCLC, but levels of TS could predict the level of response.

“In this study, 315 non-squamous NSCLC patients were first stratified as either TS-positive (more than 10% of tumor cells express TS) or TS-negative, and then randomized to cisplatin plus either pemetrexed or gemcitabine. Results were presented at the European Society of Medical Oncology (ESMO) 2014 Congress in Madrid.

“The objective response rate in the cisplatin/pemetrexed patients who were TS-negative was 47%, compared with 21.1% in the cisplatin/gemcitabine group. In the TS-positive patients, meanwhile, the objective response rates were 40.3% for cisplatin/pemetrexed patients and 39.2% for cisplatin/gemcitabine patients (P = .008).”