Merck has suffered a setback this week with the withdrawal of its application to market ridaforolimus in Europe.

The European Medicines Agency was reviewing ridaforolimus as a potential maintenance treatment for patients with soft tissue sarcoma or primary malignant bone tumour.

But in a letter to the regulator, Merck said it is pulling back the file because the Committee for Medicinal Products for Human Use has indicated that the available data are not sufficient to permit a licence for the drug in this setting.

Merck noted that it is studying ridaforolimus alongside other therapies in various tumour types, and that its withdrawal in Europe in the soft tissue sarcoma/malignant bone tumour indication does not change its commitment to ongoing trials with the drug.

But this must come as some blow to the firm, particularly as regulators across the pond knocked back the drug earlier this year.

In June, the US Food and Drug Administration issued a complete response letter for ridaforolimus, calling for additional clinical trial(s) to further assess safety and efficacy of the drug, which is also known as Taltorvic.

Merck licensed the drug, an M-TOR inhibitor - from Ariad Pharmaceuticals.