LOS ANGELES (REUTERS) - A combination of Mirati Therapeutics Inc's genetic mutation-targeting adagrasib and older cancer drug Erbitux shrank tumours in 39 per cent of patients with advanced colorectal cancer treated in a small trial, the company said on Sunday (Sept 19).

Chief Executive Officer Charles Baum told Reuters Mirati plans to meet with the US Food and Drug Administration in October to discuss whether it can pursue accelerated approval based on the combination therapy data.

Adagrasib targets a mutated form of a gene known as KRAS that occurs in around 13 per cent of non-small cell lung cancers, 3 per cent to 5 per cent of colorectal cancers and up to 2 per cent of other solid tumour cancers.

Like other newer experimental drugs, it homes in on specific gene mutations driving cancer regardless of the organ in which the disease originated.

In May, Amgen Inc's Lumakras became the first approved drug in the class after the US Food and Drug Administration cleared it for use in patients with advanced non-small cell lung cancer.

At a meeting of the European Society of Medical Oncology (ESMO) on Sunday, Mirati said that out of 28 evaluated trial patients treated with adagrasib plus Erbitux, 11, or 39 per cent, experienced tumour shrinkage.

Two patients had tumour growth, but the cancer was stabilised in the others, Mirati said.

Erbitux is an Eli Lilly & Co drug designed to block one of the signals that tells a tumor cell to grow by attaching to a structure on the cell called the epidermal growth factor receptor (EGFR).

At the ESMO meeting earlier this week, Amgen said a trial of Lumakras in combination with its own EGFR inhibitor Vectibix found that 7 out of 26 advanced colorectal cancer patients, or 27 per cent, responded to the combination therapy.

Mirati said that at the time of its analysis, with a median follow up of seven months, 63 per cent of enrolled patients remained on its combination treatment.

In a segment of the trial where colorectal cancer patients were given adagrasib alone, 22 per cent of evaluated patients responded to the drug, the company said.

Researchers said serious side effects occurred in 30 per cent of patients treated with adagrasib alone, and in 16 per cent of patients treated with the combination. Two patients who received the combination discontinued treatment after developing infusion-related reactions.

"It looks like we've gained quite a bit in efficacy and not really added much significant toxicity. So that's why, you know, that combination approach may end up being our fastest approach for accelerated approval," CEO Baum said.

Mirati plans to present updated results from a trial of adagrasib for lung cancer patients at ESMO on Monday.

Both Amgen and Mirati are also studying their drugs in combination with Keytruda, Merck & Co's blockbuster immunotherapy, for treating lung cancer.