Background Determination of thymidylate synthase (TS) levels in tumour tissue versus control tissue is useful in our hospital when selecting patients who can benefit from treatment with pemetrexed.

Purpose To compare patients with lung adenocarcinoma stage IV and low levels of TS with patients not previously investigated.

Material and methods We performed a retrospective observational study over a three-year period of patients with stage IV lung adenocarcinoma who were treated with pemetrexed.

Data collected: age, line of treatment, cycles received, ECOG, previous treatments, progression free survival (PFS) and levels of TS.

We compared patients who completed the treatment with those being followed up (routine determination of TS).

In the second group we measured PFS from the first cycle up to date (now in treatment).

Results 31 patients were enrolled on treatment: median age 62 years (56.5–66.5), median cycles of pemetrexed received 4 (3–7). 41.9% patients had ECOG 0, 48.4% ECOG 1, and 9.7% ECOG 2. 41.9% received pemetrexed in the first step, 41.9% in the second, 9.7% in the third and 6.5% in the fourth.

When the study finished: 21 patients had completed the treatment, median PFS being 1.3 months (1–3.4). Among this group, TS levels were not determined in 8 (38.1%). In the rest of patients, 12 showed low levels, only remaining high in 1 patient.

Of the 10 patients still being followed up, levels of TS were determined, with the exception of 1 (treatment initiated in 2011). All patients showed low levels, the median of stable disease being at least 6.5 months (5–13).

Conclusion Patients who start treatment without previous scoring of TS have a worse response to pemetrexed.

TS level determination is considered an indicator of the effectiveness of the treatment.

References and/or acknowledgements No conflict of interest.