Gilead Sciences' blood cancer drug Zydelig is under scrutiny by the EU regulator after reports of serious adverse events - including deaths - in clinical trials.
The European Medicines Agency (EMA) said its review of Zydelig (idelalisib) was prompted by infections seen in three trials testing the drug in combination with other cancer medicines.
Zydelig was approved in the EU in 2014 as a treatment for chronic lymphocytic leukaemia and follicular lymphoma, a form of non-Hodgkin lymphoma, and is considered an important new treatment option for these rare and incurable B cell cancers. It is also available in the US.
The three trials involved patients with CLL and indolent NHL, according to the agency, and involve either unapproved combinations or patient groups not currently included in Zydelig's labelling. However, it said the adverse event reports will be investigated "to assess whether the findings have any consequences for the authorised uses of Zydelig".
"Investigators of all clinical trials involving Zydelig are currently being informed of the actions to be taken in relation to the conduct of ongoing studies," said the EMA in a statement, adding that it is "considering whether any other immediate measures are necessary while the review is on going".
Gilead's late-stage trials programme for Zydelig includes a study looking at the drug's role as an add-on to bendamustine and Roche's MabThera/Rituxan (rituximab) in relapsed CLL patients. The trial generated positive data towards the end of last year and Gilead has said it intends to submit the data to regulators during the course of 2016.
Zydelig is an oral inhibitor of phosphoinositide 3-kinase (PI3K) delta, a protein that is thought to play a role in the activation, proliferation and viability of B cells.
The drug is a key product in Gilead's nascent oncology business, which trails behind its antiviral portfolio based on therapies for HIV and hepatitis C virus. It brought in $132m last year, a hefty increase on the $23m booked in its launch year, and has been tipped to become a $800m-plus product by 2020.
Gilead said it has halted several trials of Zydelig while the EMA investigation plays out but stands by the value of the drug in its approved indications.
The EMA's advice is that patients already taking the drug should be monitored carefully for signs of infection and treatment should not be stopped if the drug is being well tolerated.