Amgen's cancer immunotherapy T-Vec will not be granted accelerated approval by US regulators for melanoma because of trial data concerns and the increasing availability of other new therapies for the disease, official reports indicate.

T-Vec (or talimogene laherparepvec) was filed in the US with data from the Phase III OPTiM trial, which showed a 16% durable response rate and an increased median overall survival rate to 4.4 months, though the latter fell slightly short of statistical significance.

But documents posted to the US Food and Drug Administration’s website ahead of an advisory meeting Wednesday have thrown a shadow of doubt over the validity of the data, citing “uncertainty regarding the meaningfulness of the observed responses”, particularly in light of the somewhat shaky survival benefit.

Also, the regulator is questioning whether investigator bias may be behind the high drop-out rate - 278 patients - in the trial. "Subject or investigator bias regarding the relative benefit of talimogene laherparepvec and the control may have influenced the determination that it was in the best interest of the subject to stop treatment or to be given other therapy for melanoma," the documents note.

However, Amgen’s executive vice president of R&D Sean Harper stressed that the trial results show a clinical benefit to patients, and “even with the remarkable recent advances in the melanoma field, there is still a need for additional treatment options," according to Fierce Biotech.

“If approved, talimogene laherparepvec would represent an entirely new class of agent for the treatment of metastatic melanoma,” he said.